3239 lines
152 KiB
XML
3239 lines
152 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<chapter id="mvc">
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<title>Web MVC framework</title>
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<section id="mvc-introduction">
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<title>Introduction to Spring Web MVC framework</title>
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<para>The Spring Web model-view-controller (MVC) framework is designed
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around a <classname>DispatcherServlet</classname> that dispatches requests
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to handlers, with configurable handler mappings, view resolution, locale
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and theme resolution as well as support for uploading files. The default
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handler is based on the <interfacename>@Controller</interfacename> and
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<interfacename>@RequestMapping</interfacename> annotations, offering a
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wide range of flexible handling methods. With the introduction of Spring
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3.0, the <interfacename>@Controller</interfacename> mechanism also allows
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you to create RESTful Web sites and applications, through the
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<interfacename>@PathVarariable</interfacename> annotation and other
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features.</para>
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<sidebar id="mvc-open-for-extension">
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<title><quote>Open for extension...</quote></title>
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<para>A key design principle in Spring Web MVC and in Spring in general
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is the <quote><emphasis>Open for extension, closed for
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modification</emphasis></quote> principle.</para>
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<para>Some methods in the core classes of Spring Web MVC are marked
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<literal>final</literal>. As a developer you cannot override these
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methods to supply your own behavior. This has not been done arbitrarily, but
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specifically with this principal in mind.</para>
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<para>For an explanation of this principle, refer to <emphasis>Expert
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Spring Web MVC and Web Flow</emphasis> by Seth Ladd and others;
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specifically see the section "A Look At Design," on page 117 of the
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first edition. Alternatively, see</para>
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<orderedlist>
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<listitem>
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<para><ulink
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url="http://www.objectmentor.com/resources/articles/ocp.pdf">Bob
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Martin, The Open-Closed Principle (PDF)</ulink></para>
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</listitem>
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</orderedlist>
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<para>You cannot add advice to final methods when you use Spring MVC.
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For example, you cannot add advice to the
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<literal>AbstractController.handleRequest()</literal> method. Refer to
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<xref linkend="aop-understanding-aop-proxies" /> for more information on
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AOP proxies and why you cannot add advice to final methods.</para>
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</sidebar>
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<para>In Spring Web MVC you can use any object as a command or
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form-backing object; you do not need to implement a framework-specific
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interface or base class. Spring's data binding is highly flexible: for
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example, it treats type mismatches as validation errors that can be
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evaluated by the application, not as system errors. Thus you need not
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duplicate your business objects' properties as simple, untyped strings in
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your form objects simply to handle invalid submissions, or to convert the
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Strings properly. Instead, it is often preferable to bind directly to your
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business objects.</para>
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<para>Spring's view resolution is extremely flexible. A
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<interfacename>Controller</interfacename> implementation can even write
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directly to the response stream. Typically, a
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<classname>ModelAndView</classname> instance consists of a view name and a
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model <interfacename>Map</interfacename>, which contains bean names and
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corresponding objects such as a command or form, which contain reference
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data. View name resolution is highly configurable, through bean names, a
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properties file, or your own <interfacename>ViewResolver</interfacename>
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implementation. The model (the M in MVC) is based on the
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<interfacename>Map</interfacename> interface, which allows for the
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complete abstraction of the view technology. You can integrate directly
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JSP, Velocity, or any other rendering technology. The model
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<interfacename>Map</interfacename> is simply transformed into an
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appropriate format, such as JSP request attributes or a Velocity template
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model.</para>
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<section id="mvc-features">
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<title>Features of Spring Web MVC<!--I moved Features of Spring Web MVC before Pluggability of other MVC implementations. You want to highlight your own imp. first.--></title>
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<!--Second line of sidebar refers to JSF; don't you mean JSP? Other refs in this context are to JSP. Also note, sidebar is read-only.-->
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<xi:include href="swf-sidebar.xml"
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xmlns:xi="http://www.w3.org/2001/XInclude" />
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<para>Spring's web module includes many unique web support
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features:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis>Clear separation of roles</emphasis>. Each role --
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controller, validator, command object, form object, model object,
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<classname>DispatcherServlet</classname>, handler mapping, view
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resolver, and so on -- can be fulfilled by a specialized
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object.</para>
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</listitem>
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<listitem>
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<para><emphasis>Powerful and straightforward configuration of both
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framework and application classes as JavaBeans</emphasis>. This
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configuration capability includes easy referencing across contexts,
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such as from web controllers to business objects and
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validators.</para>
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</listitem>
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<listitem>
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<para><emphasis>Adaptability, non-intrusiveness, and
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flexibility.</emphasis> Define any controller method signature you
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need, possibly using one of the parameter annotations (such as
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@RequestParam, @RequestHeader, @PathVariable, and more) for a given
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scenario.</para>
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</listitem>
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<listitem>
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<para><emphasis>Reusable business code</emphasis>,<emphasis> no need
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for duplication</emphasis>. Use existing business objects as command
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or form objects instead of mirroring them to extend a particular
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framework base class.</para>
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</listitem>
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<listitem>
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<para><emphasis>Customizable binding and validation</emphasis>. Type
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mismatches as application-level validation errors that keep the
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offending value, localized date and number binding, and so on
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instead of String-only form objects with manual parsing and
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conversion to business objects.</para>
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</listitem>
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<listitem>
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<para><emphasis>Customizable handler mapping and view
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resolution</emphasis>. Handler mapping and view resolution
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strategies range from simple URL-based configuration, to
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sophisticated, purpose-built resolution strategies. Spring is more
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flexible than web MVC frameworks that mandate a particular
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technique.</para>
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</listitem>
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<listitem>
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<para><emphasis>Flexible model transfer</emphasis>. Model transfer
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with a name/value <interfacename>Map</interfacename> supports easy
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integration with any view technology.</para>
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</listitem>
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<listitem>
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<para><emphasis>Customizable locale and theme resolution, support
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for JSPs with or without Spring tag library, support for JSTL,
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support for Velocity without the need for extra bridges, and so
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on.</emphasis></para>
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</listitem>
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<listitem>
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<para><emphasis>A simple yet powerful JSP tag library known as the
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Spring tag library that provides support for features such as data
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binding and themes</emphasis>. The custom tags allow for maximum
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flexibility in terms of markup code. For information on the tag
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library descriptor, see the appendix entitled <xref
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linkend="spring.tld" /></para>
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</listitem>
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<listitem>
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<para><emphasis>A JSP form tag library, introduced in Spring 2.0,
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that makes writing forms in JSP pages much easier.</emphasis> For
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information on the tag library descriptor, see the appendix entitled
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<xref linkend="spring-form.tld" /></para>
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</listitem>
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<listitem>
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<para><emphasis>Beans whose lifecycle is scoped to the current HTTP
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request or HTTP <interfacename>Session</interfacename>.</emphasis>
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This is not a specific feature of Spring MVC itself, but rather of
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the <interfacename>WebApplicationContext</interfacename>
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container(s) that Spring MVC uses. These bean scopes are described
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in <xref linkend="beans-factory-scopes-other" /></para>
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</listitem>
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</itemizedlist>
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</section>
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<section id="mvc-introduction-pluggability">
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<title>Pluggability of other MVC implementations</title>
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<para>Non-Spring MVC implementations are preferable for some projects.
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Many teams expect to leverage their existing investment in skills and
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tools. A large body of knowledge and experience exist for the Struts
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framework. If you can abide Struts' architectural flaws, it can be a
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viable choice for the web layer; the same applies to WebWork and other
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web MVC frameworks.</para>
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<para>If you do not want to use Spring's web MVC, but intend to leverage
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other solutions that Spring offers, you can integrate the web MVC
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framework of your choice with Spring easily. Simply start up a Spring
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root application context through its
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<classname>ContextLoaderListener</classname>, and access it through
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its<!--Identify *its*. do you mean root application context's?-->
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<interfacename>ServletContext</interfacename> attribute (or Spring's
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respective helper method) from within a Struts or WebWork action. No
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"plug-ins" are involved, so no dedicated integration is necessary. From
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the web layer's point of view, you simply use Spring as a library, with
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the root application context instance as the entry point.</para>
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<para>Your registered beans and Spring's services can be at your
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fingertips even without Spring's Web MVC. Spring does not compete with
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Struts or WebWork in this scenario. It simply addresses the many areas
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that the pure web MVC frameworks do not, from bean configuration to data
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access and transaction handling. So you can enrich your application with
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a Spring middle tier and/or data access tier, even if you just want to
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use, for example, the transaction abstraction with JDBC or
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Hibernate.</para>
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</section>
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</section>
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<section id="mvc-servlet">
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<title>The <classname>DispatcherServlet</classname></title>
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<para>Spring's web MVC framework is, like many other web MVC frameworks,
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request-driven, designed around a central servlet that dispatches requests
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to controllers and offers other functionality that facilitates the
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development of web applications. Spring's
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<classname>DispatcherServlet</classname> however, does more than just
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that. It is completely integrated with the Spring IoC container and as
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such allows you to use every other feature that Spring has.</para>
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<para>The request processing workflow of the Spring Web MVC
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<classname>DispatcherServlet</classname> is illustrated in the following
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diagram. The pattern-savvy reader will recognize that the
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<classname>DispatcherServlet</classname> is an expression of the
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<quote>Front Controller</quote> design pattern (this is a pattern that
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Spring Web MVC shares with many other leading web frameworks).</para>
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<para><mediaobject>
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<imageobject role="fo">
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<imagedata align="center" fileref="images/mvc.png" format="PNG" />
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</imageobject>
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<imageobject role="html">
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<imagedata align="center" fileref="images/mvc.png" format="PNG" />
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</imageobject>
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<caption><para>The requesting processing workflow in Spring Web MVC
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(high level)</para></caption>
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</mediaobject></para>
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<para>The <classname>DispatcherServlet</classname> is an actual
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<interfacename>Servlet</interfacename> (it inherits from the
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<classname>HttpServlet</classname> base class), and as such is declared in
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the <literal>web.xml</literal> of your web application. You need to map
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requests that you want the <classname>DispatcherServlet</classname> to
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handle, by using a URL mapping in the same <literal>web.xml</literal>
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file. This is standard J2EE servlet configuration; the following example
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shows such a <classname>DispatcherServlet</classname> declaration and
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mapping:</para>
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<programlisting language="xml"><web-app>
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<servlet>
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<servlet-name>example</servlet-name>
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<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
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<load-on-startup>1</load-on-startup>
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</servlet>
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<servlet-mapping>
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<servlet-name>example</servlet-name>
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<url-pattern>*.form</url-pattern>
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</servlet-mapping>
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</web-app></programlisting>
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<para>In the preceding example, all requests ending with
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<literal>.form</literal> will be handled by the <literal>example</literal>
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<classname>DispatcherServlet</classname>. This is only the first step in
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setting up Spring Web MVC. <!--The discussion below is a little vague about what you're doing, when you do it, and what you're accomplishing. --><!-- Is the next step shown in the next example screen?-->You
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now need to configure the various beans used by the Spring Web MVC
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framework (over and above the <classname>DispatcherServlet</classname>
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itself).<!--See previous sentence.Add info to indicate where you find info that tells you how to configure beans for MVC framework. --><!--Next paragraph, so what are you telling them to *do* here? --></para>
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<para>As detailed in <xref linkend="context-introduction" />,
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<interfacename>ApplicationContext</interfacename> instances in Spring can
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be scoped. In the Web MVC framework, each
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<classname>DispatcherServlet</classname> has its own
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<interfacename>WebApplicationContext</interfacename>, which inherits all
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the beans already defined in the root
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<interfacename>WebApplicationContext</interfacename>. These inherited
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beans defined can be overridden in the servlet-specific scope, <!--Preceding line is garbled; how should it read?-->and
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you can define new scope-specific beans local to a given servlet
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instance.</para>
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<para><mediaobject>
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<imageobject role="fo">
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<imagedata align="center" fileref="images/mvc-contexts.gif"
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format="GIF" />
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</imageobject>
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<imageobject role="html">
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<imagedata align="center" fileref="images/mvc-contexts.gif"
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format="GIF" />
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</imageobject>
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<caption>Context hierarchy in Spring Web MVC</caption>
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</mediaobject></para>
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<para>Upon initialization of a <classname>DispatcherServlet</classname>,
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the framework <!--Spring MVC or Spring Framework?--><emphasis><emphasis>looks
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for a file named</emphasis>
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<literal>[servlet-name]-servlet.xml</literal></emphasis> in the
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<literal>WEB-INF</literal> directory of your web application and create
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the beans defined there, overriding the definitions of any beans defined
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with the same name in the global scope.</para>
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<para>Consider the following <classname>DispatcherServlet</classname>
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servlet configuration (in the <literal>web.xml</literal> file):</para>
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<programlisting language="xml"><web-app>
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<servlet>
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<servlet-name><emphasis role="bold">golfing</emphasis></servlet-name>
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<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
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<load-on-startup>1</load-on-startup>
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</servlet>
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<servlet-mapping>
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<servlet-name><emphasis role="bold">golfing</emphasis></servlet-name>
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<url-pattern>/golfing/*</url-pattern>
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</servlet-mapping>
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</web-app></programlisting>
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<para>With the above servlet configuration in place, <!--Is this something you need to do (in above example)? -->you
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will need to have a file called <literal>/WEB-INF/<emphasis
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role="bold">golfing</emphasis>-servlet.xml</literal> in your application;
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this file will contain all of your Spring Web MVC-specific components
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(beans). You can change the exact location of this configuration file
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through a servlet initialization parameter (see below for details).
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</para>
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<!--See *where* for details? Give x-ref to section talks about how to change the location of the file through servlet init. param.-->
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<para>The <interfacename>WebApplicationContext</interfacename> is an
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extension of the plain <interfacename>ApplicationContext</interfacename>
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that has some extra features necessary for web applications. It differs
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from a normal <interfacename>ApplicationContext</interfacename> in that it
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is capable of resolving themes (see <xref linkend="mvc-themeresolver" />),
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and that it knows which servlet it is associated with (by having a link to
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the <interfacename>ServletContext</interfacename>). The
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<interfacename>WebApplicationContext</interfacename> is bound in the
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<interfacename>ServletContext</interfacename>, and by using static methods
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on the <classname>RequestContextUtils</classname> class you can always
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look up the <interfacename>WebApplicationContext</interfacename> if you
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need access to it.</para>
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<para>The Spring <classname>DispatcherServlet</classname> uses special
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beans to process requests and render the appropriate views. These beans
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are part of Spring Framework. You can configure them in the
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<interfacename>WebApplicationContext</interfacename>, just as you
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configure any other bean. However, for most beans, sensible defaults are
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provided so you initially do not need to configure them. <!--Which beans have defaults? What do you mean you *initially* don't need to configure them? What determines whether you need to and --><!--when, if not *initially*? In table below, indicate which are defaults, which have to be configured.-->These
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beans are described in the following table. </para>
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<table id="mvc-webappctx-special-beans-tbl">
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<title>Special beans in the
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<interfacename>WebApplicationContext</interfacename></title>
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<tgroup cols="2">
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<colspec colname="c1" colwidth="1*" />
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<colspec colname="c2" colwidth="4*" />
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<thead>
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<row>
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<entry>Bean type</entry>
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<entry>Explanation</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><link linkend="mvc-controller">controllers</link></entry>
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<entry>Form the <literal>C</literal> part of the MVC.<!--Need info about controller function as with others in this list.Reader knows what C stands for.--></entry>
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</row>
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<row>
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<entry><link linkend="mvc-handlermapping">handler
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mappings</link></entry>
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<entry>Handle the execution of a list of pre-processors and
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post-processors and controllers that will be executed if they
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match certain criteria (for example, a matching URL specified with
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the controller).</entry>
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</row>
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<row>
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<entry><link linkend="mvc-viewresolver">view
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resolvers</link></entry>
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<entry>Resolves view names to views.<!--If it's capable of resolving, just say *resolves*. Like above, handler mappings are capable of handling the execution, but you just say *handle the execution*--></entry>
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</row>
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<row>
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<entry> <link linkend="mvc-localeresolver">locale
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resolver</link></entry>
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<entry>A <link linkend="mvc-localeresolver">locale resolver</link>
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is a component capable of resolving the locale a client is using,
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in order to be able to offer internationalized views</entry>
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</row>
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<row>
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<entry>Theme resolver</entry>
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<entry>A <link linkend="mvc-themeresolver">theme resolver</link>
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is capable of resolving themes your web application can use, for
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example, to offer personalized layouts</entry>
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</row>
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<row>
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<entry>multipart file resolver</entry>
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<entry>Contains functionality to process file uploads from HTML
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forms.<!--Here and next one, why not just say processes file uploads, maps executions instead of *contains functionality to*?--></entry>
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</row>
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<row>
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<entry><link linkend="mvc-exceptionhandlers">handler exception
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resolvers</link></entry>
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<entry> Contains functionality to map exceptions to views or
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implement other more complex exception handling code.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>After you set up a <classname>DispatcherServlet</classname>, and a
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request comes in for that specific
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<classname>DispatcherServlet</classname>, the
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<classname>DispatcherServlet</classname> starts processing the request as
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follows:</para>
|
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|
|
<orderedlist>
|
|
<listitem>
|
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<para>The <interfacename>WebApplicationContext</interfacename> is
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searched for and bound in the request as an attribute that the
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controller and other elements in the process can use. <!--Use to do *what*? Also revise to indicate *what* searches for the WebApplicationContext -->It
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is bound by default under the key
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<literal>DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE</literal>.</para>
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</listitem>
|
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|
|
<listitem>
|
|
<para>The locale resolver is bound to the request to enable elements
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in the process to resolve the locale to use when processing the
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request (rendering the view, preparing data, and so on). If you do not
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need locale resolving, you do not need it.</para>
|
|
<!--Reword 'if you don't need local resolving, you dont need to use it '. Are you saying locale resolving is optional? If you don't configure it, will this step occur?-->
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>The theme resolver is bound to the request to let elements such
|
|
as views determine which theme to use. If you do not use themes, you
|
|
can ignore it.</para>
|
|
<!-- MLP perhaps say that there are not side effect to this binding.etc... Clarify *ignore it*. Does this step still occur if you don't use themes? --><!--And what if you DO use themes, what do you do and when? Same question re locale resolving.-->
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If you specify a multipart file resolver, the request is
|
|
inspected for multiparts; if multiparts are found, the request is
|
|
wrapped in a <classname>MultipartHttpServletRequest</classname> for
|
|
further processing by other elements in the process. (See <xref
|
|
linkend="mvc-multipart-resolver" /> for further information about
|
|
multipart handling).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>An appropriate handler is searched for. If a handler is found,
|
|
the execution chain associated with the handler (preprocessors,
|
|
postprocessors, and controllers) is executed in order to prepare a
|
|
model or rendering.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If a model is returned, the view is rendered. If no model is
|
|
returned, (may be due to a preprocessor or postprocessor
|
|
intercepting the request, perhaps for security reasons), no view is
|
|
rendered, because the request could already have been fulfilled.</para>
|
|
<!--fulfilled how and by what?-->
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>Handler exception resolvers that are declared in the
|
|
<interfacename>WebApplicationContext</interfacename> pick up exceptions
|
|
that are thrown during processing of the request. Using these exception
|
|
resolvers allows you to define custom behaviors to address
|
|
exceptions.</para>
|
|
|
|
<para>The Spring <classname>DispatcherServlet</classname> also supports
|
|
the return of the <emphasis>last-modification-date</emphasis>, as
|
|
specified by the Servlet API. The process of determining the last
|
|
modification date for a specific request is straightforward: the
|
|
<classname>DispatcherServlet</classname> looks up an appropriate handler
|
|
mapping and tests whether the handler that is found
|
|
implements the
|
|
</emphasis><interfacename>LastModified</interfacename></emphasis>
|
|
interface. If so, the value of the <literal>long
|
|
getLastModified(request)</literal> method of the
|
|
<interfacename>LastModified</interfacename> interface is returned to the
|
|
client.</para>
|
|
|
|
<para>You can customize Spring's <classname>DispatcherServlet</classname>
|
|
by adding context parameters in the <literal>web.xml</literal> file or
|
|
servlet initialization parameters. See the following table.</para>
|
|
<!--Reword above sentence to specify whether configuring parameters in table configures last-modification-date, or are they further --><!--customization for some other purpose? If so, need to explain how you config last-modification-date-->
|
|
|
|
<table id="mvc-disp-servlet-init-params-tbl">
|
|
<title><classname>DispatcherServlet</classname> initialization
|
|
parameters</title>
|
|
|
|
<tgroup cols="2">
|
|
<colspec colname="c1" colwidth="1*" />
|
|
|
|
<colspec colname="c2" colwidth="4*" />
|
|
|
|
<thead>
|
|
<row>
|
|
<entry>Parameter</entry>
|
|
|
|
<entry>Explanation</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry><literal>contextClass</literal></entry>
|
|
|
|
<entry>Class that implements
|
|
<interfacename>WebApplicationContext</interfacename>, which
|
|
instantiates the context used by this servlet. By default, the
|
|
<classname>XmlWebApplicationContext</classname> is used.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><literal>contextConfigLocation</literal></entry>
|
|
|
|
<entry>String that is passed to the context instance (specified by
|
|
<literal>contextClass</literal>) to indicate where context(s) can
|
|
be found. The string consists potentially of multiple strings
|
|
(using a comma as a delimiter) to support multiple contexts. In
|
|
case of multiple context locations with beans that are defined
|
|
twice, the latest location takes precedence.</entry>
|
|
<!-- MLP review -->
|
|
</row>
|
|
|
|
<row>
|
|
<entry><literal>namespace</literal></entry>
|
|
|
|
<entry>Namespace of the
|
|
<interfacename>WebApplicationContext</interfacename>. Defaults to
|
|
<literal>[servlet-name]-servlet</literal>.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</section>
|
|
|
|
<section id="mvc-controller">
|
|
<title>Implementing Controllers</title>
|
|
|
|
<para>Controllers provide access to the application behavior that you
|
|
typically define through a service interface. <!--I changed preceding to active voice because next sentence refers to user input. Thus *you* do some defining.-->Controllers
|
|
interpret user input and transform it into a model that is represented to
|
|
the user by the view. Spring implements a controller in a very abstract
|
|
way, which enables you to create a wide variety of controllers.</para>
|
|
|
|
<para>Spring 2.5 introduced an annotation-based programming model for MVC
|
|
controllers that uses annotations such as
|
|
<interfacename>@RequestMapping</interfacename>,
|
|
<interfacename>@RequestParam</interfacename>,
|
|
<interfacename>@ModelAttribute</interfacename>, and so on. This annotation
|
|
support is available for both Servlet MVC and Portlet MVC. Controllers
|
|
implemented in this style do not have to extend specific base classes or
|
|
implement specific interfaces. Furthermore, they do not usually have
|
|
direct dependencies on Servlet or Portlet APIs, although you can easily
|
|
configure access to Servlet or Portlet facilities.</para>
|
|
|
|
<tip>
|
|
<para>The Spring distribution ships with the
|
|
<emphasis>PetClinic</emphasis> sample, a web application that leverages
|
|
the annotation support described in this section, in the context of
|
|
simple form processing. The <emphasis>PetClinic</emphasis> application
|
|
resides in the <literal>samples/petclinic</literal> directory.</para>
|
|
|
|
<!-- MLP Note removed reference to imagedb -->
|
|
</tip>
|
|
|
|
<!--You need an intro sentence here that indicates the *purpose* of the following code. -->
|
|
|
|
<programlisting language="java">@Controller
|
|
public class HelloWorldController {
|
|
|
|
@RequestMapping("/helloWorld")
|
|
public ModelAndView helloWorld() {
|
|
ModelAndView mac = new ModelAndView();
|
|
mav.setViewName("helloWorld");
|
|
mav.addObject("message", "Hello World!");
|
|
return mav;
|
|
}
|
|
}</programlisting>
|
|
|
|
<para>As you can see, the <interfacename>@Controller</interfacename> and
|
|
<interfacename>@RequestMapping</interfacename> annotations allow flexible
|
|
method names and signatures. In this particular example the method has no
|
|
parameters and returns a <classname>ModelAndView</classname>, but various
|
|
other (and better) strategies exist, <!--strategies for doing *what*? -->as
|
|
are explained later in this section. <classname>ModelAndView</classname>,
|
|
<interfacename>@Controller</interfacename>, and
|
|
<interfacename>@RequestMapping</interfacename> form the basis for the
|
|
Spring MVC implementation. This section documents these annotations and
|
|
how they are most commonly used in a Servlet environment.</para>
|
|
|
|
<section id="mvc-ann-controller">
|
|
<title>Defining a controller with
|
|
<interfacename>@Controller</interfacename></title>
|
|
|
|
<para>The <interfacename>@Controller</interfacename> annotation
|
|
indicates that a particular class serves the role of a
|
|
<emphasis>controller</emphasis>. Spring does not require you to extend
|
|
any controller base class or reference the Servlet API. However, you can
|
|
still reference Servlet-specific features if you need to do so.</para>
|
|
|
|
<para>The <interfacename>@Controller</interfacename> annotation acts as
|
|
a stereotype for the annotated class, indicating its role. The
|
|
dispatcher scans such annotated classes for mapped methods and detects
|
|
<interfacename>@RequestMapping</interfacename> annotations (see the next
|
|
section).</para>
|
|
|
|
<para>You can define annotated controller beans explicitly, using a
|
|
standard Spring bean definition in the dispatcher's context. However,
|
|
the <interfacename>@Controller</interfacename> stereotype also allows
|
|
for autodetection, aligned with Spring general support for detecting
|
|
component classes in the classpath and auto-registering bean definitions
|
|
for them.</para>
|
|
<!-- MLP Bev.changed to 'also supports autodetection -->
|
|
<para>To enable autodetection of such annotated controllers, you add
|
|
component scanning to your configuration. Use the
|
|
<emphasis>spring-context</emphasis> schema as shown in the following XML
|
|
snippet:</para>
|
|
|
|
<programlisting language="xml"><?xml version="1.0" encoding="UTF-8"?>
|
|
<beans xmlns="http://www.springframework.org/schema/beans"
|
|
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
|
|
xmlns:p="http://www.springframework.org/schema/p"
|
|
xmlns:context="http://www.springframework.org/schema/context"
|
|
xsi:schemaLocation="
|
|
http://www.springframework.org/schema/beans
|
|
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
|
|
http://www.springframework.org/schema/context
|
|
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
|
|
|
|
<context:component-scan base-package="org.springframework.samples.petclinic.web"/>
|
|
|
|
<lineannotation>// ...</lineannotation>
|
|
|
|
</beans></programlisting>
|
|
</section>
|
|
|
|
<section id="mvc-ann-requestmapping">
|
|
<title>Mapping requests with
|
|
<interfacename>@RequestMapping</interfacename></title>
|
|
|
|
<para>You use the <interfacename>@RequestMapping</interfacename>
|
|
annotation to map URLs such as <filename>/appointments</filename> onto
|
|
an entire class or a particular handler method. You can use it to
|
|
annotate both a class and a method. Typically the class-level annotation
|
|
maps a specific request path (or path pattern) onto a form controller,
|
|
with additional method-level annotations narrowing the primary mapping
|
|
for a specific HTTP method request method ("GET"/"POST") or specific
|
|
HTTP request parameters.</para>
|
|
|
|
<para>The following example shows a controller from the PetClinic sample
|
|
application that uses this annotation:</para>
|
|
|
|
<programlisting language="java">@Controller
|
|
<emphasis role="bold">@RequestMapping("/appointments")</emphasis>
|
|
public class AppointmentsController {
|
|
|
|
private AppointmentBook appointmentBook;
|
|
|
|
@Autowired
|
|
public AppointmentsController(AppointmentBook appointmentBook) {
|
|
this.appointmentBook = appointmentBook;
|
|
}
|
|
|
|
<emphasis role="bold">@RequestMapping(method = RequestMethod.GET)</emphasis>
|
|
public Appointments get() {
|
|
return appointmentBook.getAppointmentsForToday();
|
|
}
|
|
|
|
<emphasis role="bold">@RequestMapping(value="/{day}", method = RequestMethod.GET)</emphasis>
|
|
public void getForDay(@PathVariable Date day, ExternalContext context) {
|
|
Appointments appts = appointmentBook.getAppointmentsForDay(day);
|
|
context.getModel().addAttribute(appts);
|
|
context.selectView("appointments");
|
|
if (context.isAjaxRequest()) {
|
|
//could activate a ViewHelper for component associated with main
|
|
context.renderFragment("main");
|
|
}
|
|
}
|
|
|
|
<emphasis role="bold">@RequestMapping(value="/new", method = RequestMethod.GET)</emphasis>
|
|
public AppointmentForm getNewForm() {
|
|
return new AppointmentForm();
|
|
}
|
|
|
|
<emphasis role="bold">@RequestMapping(method = RequestMethod.POST)</emphasis>
|
|
public String post(AppointmentForm form) {
|
|
appointmentBook.createAppointment(form);
|
|
return "redirect:/appointments";
|
|
}
|
|
}</programlisting>
|
|
|
|
<para>In the example, the <interfacename>@RequestMapping</interfacename>
|
|
is used in a number of places. The first usage is on the type (class)
|
|
level, which indicates that all handling methods on this controller are
|
|
relative to the <filename>/appointments</filename> path. The
|
|
<methodname>get()</methodname> method has a further
|
|
<interfacename>@RequestMapping</interfacename> refinement: it only
|
|
accepts GET requests, meaning that an HTTP GET for
|
|
<filename>/appointments</filename> invokes this method. The
|
|
<methodname>post()</methodname> has a similar refinement, and the
|
|
<methodname>getNewForm()</methodname> combines the definition of HTTP
|
|
method and path into one, so that GET requests for
|
|
<filename>appointments/new</filename> are handled by that method.</para>
|
|
|
|
<para>The <methodname>getForDay()</methodname> method shows another
|
|
usage of <interfacename>@RequestMapping</interfacename>: URI templates.
|
|
(See <link linkend="mvc-ann-requestmapping-uri-templates">the next
|
|
section </link>).</para>
|
|
|
|
<para>A <interfacename>@RequestMapping</interfacename> on the class
|
|
level is not required. Without it, all paths are simply absolute, and
|
|
not relative. The following example from the PetClinic sample
|
|
application shows a multi-action controller using
|
|
<classname>@RequestMapping</classname>:</para>
|
|
|
|
<programlisting language="java">@Controller
|
|
public class ClinicController {
|
|
|
|
private final Clinic clinic;
|
|
|
|
@Autowired
|
|
public ClinicController(Clinic clinic) {
|
|
this.clinic = clinic;
|
|
}
|
|
|
|
<emphasis role="bold">@RequestMapping("/")</emphasis>
|
|
public void welcomeHandler() {
|
|
}
|
|
|
|
<emphasis role="bold">@RequestMapping("/vets")</emphasis>
|
|
public ModelMap vetsHandler() {
|
|
return new ModelMap(this.clinic.getVets());
|
|
}
|
|
|
|
}</programlisting>
|
|
|
|
<section id="mvc-ann-requestmapping-uri-templates">
|
|
<title>URI Templates</title>
|
|
|
|
<para>To access parts of a request URL in your handling methods, use
|
|
the <emphasis><emphasis>URI templates</emphasis></emphasis> in the
|
|
<interfacename>@RequestMapping</interfacename> path value.</para>
|
|
|
|
<sidebar id="mvc-uri-templates">
|
|
<title>URI Templates</title>
|
|
|
|
<para>A URI Template is a URI-like string, containing one or more
|
|
variable names. When you substitute values for these variables, the
|
|
template becomes a URI. The <ulink
|
|
url="http://bitworking.org/projects/URI-Templates/">proposed
|
|
RFC</ulink> for URI Templates defines how a URI is parameterized.
|
|
For example, the URI Template</para>
|
|
|
|
<programlisting>http://www.example.com/users/{userid}</programlisting>
|
|
|
|
<para>contains the variable <emphasis>userid</emphasis>. If we
|
|
assign the variable the value fred, the URI Template yields:</para>
|
|
|
|
<programlisting>http://www.example.com/users/fred</programlisting>
|
|
|
|
<para>During the processing of a request, the URI can be compared to
|
|
an expected URI Template in order to extract a collection of
|
|
variables.</para>
|
|
</sidebar>
|
|
|
|
<para>You use the <interfacename>@PathVariable</interfacename> method
|
|
parameter annotation to indicate that a method parameter should be
|
|
bound to the value of a URI template variable.</para>
|
|
|
|
<para>The following code snippet shows the use of a single
|
|
<interfacename>@PathVariable</interfacename> in a controller
|
|
method:</para>
|
|
|
|
<programlisting language="java">@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
|
|
public String findOwner(<emphasis role="bold">@PathVariable</emphasis> String ownerId, Model model) {
|
|
Owner owner = ownerService.findOwner(ownerId);
|
|
model.addAttribute("owner", owner);
|
|
return "displayOwner";
|
|
}
|
|
</programlisting>
|
|
|
|
<para>The URI Template "<literal>/owners/{ownerId}</literal>"
|
|
specifies the variable name <emphasis>ownerId</emphasis>. When the
|
|
controller handles this request, the value of
|
|
<emphasis>ownerId</emphasis> is set to the value in the request URI.
|
|
For example, when a request comes in for /owners/fred, the value fred
|
|
is bound to the method parameter <literal>String
|
|
ownerId</literal>.</para>
|
|
|
|
<!-- MLP: Bev Review -->
|
|
<para>The matching of method parameter names to URI Template variable
|
|
names can only be done if your code is compiled with debugging
|
|
enabled. If you do have not debugging enabled, you must specify the
|
|
name of the URI Template variable name in the @PathVariable annotation
|
|
in order to bind the resovled value of the variable name to a
|
|
method parameter. For example:</para>
|
|
|
|
<programlisting language="java">@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
|
|
public String findOwner(<emphasis role="bold">@PathVariable</emphasis>("ownerId") String ownerId, Model model) {
|
|
// implementation omitted
|
|
}
|
|
</programlisting>
|
|
<para>
|
|
so you can also use a controller method with the following
|
|
signature:</para>
|
|
|
|
<programlisting language="java">@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
|
|
public String findOwner(<emphasis role="bold">@PathVariable</emphasis>("ownerId") String theOwner, Model model) {
|
|
// implementation omitted
|
|
}</programlisting>
|
|
|
|
<para>You can use multiple @PathVariable annotations to bind <!--specify: to bind *what* to multiple URI template variables? method parameter String ownerId?-->to
|
|
multiple URI Template variables:</para>
|
|
|
|
<programlisting language="java">@RequestMapping(value="/owners/{ownerId}/pets/{petId}", method=RequestMethod.GET)
|
|
public String findPet(<emphasis role="bold">@PathVariable</emphasis> String ownerId, <emphasis
|
|
role="bold">@PathVariable</emphasis> String petId, Model model) {
|
|
Owner owner = ownerService.findOwner(ownderId);
|
|
Pet pet = owner.getPet(petId);
|
|
model.addAttribute("pet", pet);
|
|
return "displayPet";
|
|
}
|
|
</programlisting>
|
|
|
|
<para>The following code snippet shows the use of path variables on a
|
|
relative path, so that the <methodname>findPet()</methodname> method
|
|
will be invoked for <filename>/owners/42/pets/21</filename>, for
|
|
instance.</para>
|
|
|
|
<programlisting language="java">@Controller
|
|
@RequestMapping(<emphasis role="bold">"/owners/{ownerId}"</emphasis>)
|
|
public class RelativePathUriTemplateController {
|
|
|
|
@RequestMapping(<emphasis role="bold">"/pets/{petId}"</emphasis>)
|
|
public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
|
|
// implementation omitted
|
|
}
|
|
}
|
|
</programlisting>
|
|
|
|
<tip>
|
|
<para>Method parameters that are decorated with the
|
|
<interfacename>@PathVariable</interfacename> annotation can be of
|
|
<emphasis role="bold">any simple type </emphasis>such as int, long,
|
|
Date... Spring automatically converts to the appropriate type and
|
|
throws a <classname>TypeMismatchException</classname> if the type is
|
|
not correct. You can further customize this conversion process by
|
|
customizing the data binder. See <xref
|
|
linkend="mvc-ann-webdatabinder" />.</para>
|
|
</tip>
|
|
</section>
|
|
|
|
<section id="mvc-ann-requestmapping-advanced">
|
|
<title>Advanced <interfacename>@RequestMapping</interfacename>
|
|
options</title>
|
|
|
|
<para>In addition to URI templates, the
|
|
<interfacename>@RequestMapping</interfacename> annotation also
|
|
supports Ant-style path patterns (for example,
|
|
<filename>/myPath/*.do</filename>). A combination of URI templates and
|
|
Ant-style globs is also supported (for example,
|
|
<filename>/owners/*/pets/{petId}</filename>).</para>
|
|
|
|
<para>The handler method names are taken into account for narrowing if
|
|
no path was specified explicitly, according to the specified
|
|
<interfacename>org.springframework.web.servlet.mvc.multiaction.MethodNameResolver</interfacename>
|
|
(by default an
|
|
<classname>org.springframework.web.servlet.mvc.multiaction.InternalPathMethodNameResolver</classname>).
|
|
This only applies if annotation mappings do not specify a path mapping
|
|
explicitly. In other words, the method name is only used for narrowing
|
|
among a set of matching methods; it does not constitute a primary path
|
|
mapping itself.</para>
|
|
|
|
<para>If you have a single default method (without explicit path
|
|
mapping), then all requests without a more specific mapped method
|
|
found are dispatched to it. If you have multiple such default methods,
|
|
then the method name is taken into account for choosing between
|
|
them.</para>
|
|
|
|
<para>You can narrow path mappings through parameter conditions: a
|
|
sequence of "myParam=myValue" style expressions, with a request only
|
|
mapped if each such parameter is found to have the given value. For
|
|
example: <programlisting language="java">@Controller
|
|
@RequestMapping("/owners/{ownerId}")
|
|
public class RelativePathUriTemplateController {
|
|
|
|
@RequestMapping(value = "/pets/{petId}", <emphasis role="bold">params="myParam=myValue"</emphasis>)
|
|
public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
|
|
// implementation omitted
|
|
}
|
|
}
|
|
</programlisting> "myParam" style expressions are also supported, with such
|
|
parameters having to be present in the request (allowed to have any
|
|
value). <!--I don't understand the preceding sentence. Can you reword?-->Finally,
|
|
"!myParam" style expressions indicate that the specified parameter is
|
|
<emphasis>not</emphasis> supposed to be present in the request.</para>
|
|
|
|
<para>Similarly, path mappings can be narrowed down through header
|
|
conditions: <programlisting language="java">@Controller
|
|
@RequestMapping("/owners/{ownerId}")
|
|
public class RelativePathUriTemplateController {
|
|
|
|
@RequestMapping(value = "/pets", method = RequestMethod.POST, <emphasis
|
|
role="bold">headers="content-type=text/*"</emphasis>)
|
|
public void addPet(Pet pet, @PathVariable String ownerId) {
|
|
// implementation omitted
|
|
}
|
|
}
|
|
</programlisting> In the above example, the <methodname>addPet</methodname> is
|
|
only invoked when the content-type is in the <literal>text/*</literal>
|
|
range, for example, <literal>text/xml</literal>.</para>
|
|
</section>
|
|
|
|
<section id="mvc-ann-requestmapping-arguments">
|
|
<title>Supported handler method arguments and return types</title>
|
|
|
|
<para>Handler methods that are annotated with
|
|
<classname>@RequestMapping</classname> can have very flexible
|
|
signatures. They may have arguments of the following types, in
|
|
arbitrary order. (except for validation results, which need to follow
|
|
right after the corresponding command object, if desired<!--Reword preceding sentence to clarify, make it a complete sentence and no parentheses: first it says validation results *must*--><!--immediately follow command object, but then it says *if desired*. Clarify what must happen if what is desired. And are validation --><!-- results a type of argument? Relate to the sentence that precedes it.-->):
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Request and/or response objects (Servlet API). Choose any
|
|
specific request/response type, for example,
|
|
<interfacename>ServletRequest</interfacename> /
|
|
<interfacename>HttpServletRequest</interfacename>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Session object (Servlet API): of type
|
|
<interfacename>HttpSession</interfacename>. An argument of this
|
|
type enforces the presence of a corresponding session. As a
|
|
consequence, such an argument is never
|
|
<literal>null</literal>.</para>
|
|
|
|
<note>
|
|
<para>Session access may not be thread-safe, in particular in
|
|
a Servlet environment: Consider switching the
|
|
<classname>AnnotationMethodHandlerAdapter</classname>'s
|
|
"synchronizeOnSession" flag to "true" if multiple requests are
|
|
allowed to access a session concurrently.</para>
|
|
</note>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>org.springframework.web.context.request.WebRequest</classname>
|
|
or
|
|
<classname>org.springframework.web.context.request.NativeWebRequest</classname>.
|
|
Allows for generic request parameter access as well as
|
|
request/session attribute access, without ties to the native
|
|
Servlet/Portlet API.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>java.util.Locale</classname> for the current
|
|
request locale, determined by the most specific locale resolver
|
|
available, in effect, the configured
|
|
<interfacename>LocaleResolver</interfacename> in a Servlet
|
|
environment.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>java.io.InputStream</classname> /
|
|
<classname>java.io.Reader</classname> for access to the
|
|
request's content. This value is the raw InputStream/Reader as
|
|
exposed by the Servlet API.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>java.io.OutputStream</classname> /
|
|
<classname>java.io.Writer</classname> for generating the
|
|
response's content. This value is the raw OutputStream/Writer as
|
|
exposed by the Servlet API.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>@PathVariabe</classname> annotated parameters
|
|
for access to URI template variables. See <xref
|
|
linkend="mvc-ann-requestmapping-uri-templates" />.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>@RequestParam</classname> annotated parameters
|
|
for access to specific Servlet request parameters. Parameter
|
|
values are converted to the declared method argument type. See
|
|
<xref linkend="mvc-ann-requestparam" />.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>@RequestHeader</classname> annotated parameters
|
|
for access to specific Servlet request HTTP headers. Parameter
|
|
values are converted to the declared method argument
|
|
type.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>@RequestBody</classname> annotated parameters
|
|
for access to the request HTTP body. Parameter values are
|
|
converted to the declared method argument type using
|
|
<interfacename>HttpMessageConverter</interfacename>s. See <xref
|
|
linkend="mvc-ann-requestbody" />.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><interfacename>java.util.Map</interfacename> /
|
|
<interfacename>org.springframework.ui.Model</interfacename> /
|
|
<classname>org.springframework.ui.ModelMap</classname> for
|
|
enriching the implicit model that is exposed to the web
|
|
view.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Command or form objects to bind parameters to: as bean
|
|
properties or fields, <!--What do you mean by *as bean properties or fields*, what does that refer to? Why do you have a colon? Don't get this line.--><!--*to bind parameters to* is awkward. Avoid slashes as with *command/form objects*. Do you mean command or form objects? Revise.-->with
|
|
customizable type conversion, depending on
|
|
<classname>@InitBinder</classname> methods and/or the
|
|
HandlerAdapter configuration. See the
|
|
<literal>webBindingInitializer</literal> property on
|
|
<classname>AnnotationMethodHandlerAdapter</classname>. Such
|
|
command objects along with their validation results will be
|
|
exposed as model attributes by default., using the non-qualified
|
|
command class name in property notation. <!--Who or what uses the non-qualified class name in property notation? Is this something you have to set up?-->For
|
|
example, "orderAddress" for type "mypackage.OrderAddress".
|
|
Specify a parameter-level <classname>ModelAttribute</classname>
|
|
annotation for declaring a specific model attribute name.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>org.springframework.validation.Errors</classname>
|
|
/
|
|
<classname>org.springframework.validation.BindingResult</classname>
|
|
validation results for a preceding command or form object (the
|
|
immediately preceding argument).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>org.springframework.web.bind.support.SessionStatus</classname>
|
|
status handle for marking form processing as complete, which
|
|
triggers the cleanup of session attributes that have been
|
|
indicated by the <classname>@SessionAttributes</classname>
|
|
annotation at the handler type level.</para>
|
|
</listitem>
|
|
</itemizedlist></para>
|
|
|
|
<para>The following return types are supported for handler methods:
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>A <classname>ModelAndView</classname> object, with the
|
|
model implicitly enriched with command objects and the results
|
|
of <literal>@ModelAttribute</literal> annotated reference data
|
|
accessor methods.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>A <interfacename>Model</interfacename> object, with the
|
|
view name implicitly determined through a
|
|
<interfacename>RequestToViewNameTranslator</interfacename> and
|
|
the model implicitly enriched with command objects and the
|
|
results of <literal>@ModelAttribute</literal> annotated
|
|
reference data accessor methods.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>A <interfacename>Map</interfacename> object for exposing a
|
|
model, with the view name implicitly determined through a
|
|
<interfacename>RequestToViewNameTranslator</interfacename> and
|
|
the model implicitly enriched with command objects and the
|
|
results of <literal>@ModelAttribute</literal> annotated
|
|
reference data accessor methods.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>A <interfacename>View</interfacename> object, with the
|
|
model implicitly determined through command objects and
|
|
<literal>@ModelAttribute</literal> annotated reference data
|
|
accessor methods. The handler method may also programmatically
|
|
enrich the model by declaring a
|
|
<interfacename>Model</interfacename> argument (see above).<!--see above where? Need more explicit reference. same problem with next item.--></para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>A <classname>String</classname> value that is interpreted
|
|
as the view name, with the model implicitly determined through
|
|
command objects and <literal>@ModelAttribute</literal> annotated
|
|
reference data accessor methods. The handler method may also
|
|
programmatically enrich the model by declaring a
|
|
<interfacename>Model</interfacename> argument (see
|
|
above).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><literal>void</literal> if the method handles the response
|
|
itself (by writing the response content directly, declaring an
|
|
argument of type <interfacename>ServletResponse</interfacename>
|
|
/ <interfacename>HttpServletResponse</interfacename> for that
|
|
purpose) or if the view name is supposed to be implicitly
|
|
determined through a
|
|
<interfacename>RequestToViewNameTranslator</interfacename> (not
|
|
declaring a response argument in the handler method
|
|
signature).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If the method is annotated with
|
|
<interfacename>@ResponseBody</interfacename>, the return type is
|
|
written to the response HTTP body. The return value will be
|
|
converted to the declared method argument type using
|
|
<interfacename>HttpMessageConverter</interfacename>s. See <xref
|
|
linkend="mvc-ann-responsebody" />.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Any other return type is considered as single model
|
|
attribute to be exposed to the view, using the attribute name
|
|
specified through <literal>@ModelAttribute</literal> at the
|
|
method level (or the default attribute name based on the return
|
|
type class name). The model is implicitly enriched with command
|
|
objects and the results of <literal>@ModelAttribute</literal>
|
|
annotated reference data accessor methods.</para>
|
|
</listitem>
|
|
</itemizedlist></para>
|
|
</section>
|
|
|
|
<section id="mvc-ann-requestparam">
|
|
<title>Binding request parameters to method parameters with
|
|
<classname>@RequestParam</classname></title>
|
|
|
|
<para>Use the <classname>@RequestParam</classname> annotation to bind
|
|
request parameters to a method parameter in your controller.</para>
|
|
|
|
<para>The following code snippet shows the usage:</para>
|
|
|
|
<programlisting language="java">@Controller
|
|
@RequestMapping("/pets")
|
|
@SessionAttributes("pet")
|
|
public class EditPetForm {
|
|
|
|
<lineannotation>// ...</lineannotation>
|
|
|
|
@RequestMapping(method = RequestMethod.GET)
|
|
public String setupForm(<emphasis role="bold">@RequestParam("petId") int petId</emphasis>, ModelMap model) {
|
|
Pet pet = this.clinic.loadPet(petId);
|
|
model.addAttribute("pet", pet);
|
|
return "petForm";
|
|
}
|
|
|
|
<lineannotation>// ...</lineannotation>
|
|
</programlisting>
|
|
|
|
<para>Parameters using this annotation are required by default, but
|
|
you can specify that a parameter is optional by setting
|
|
<interfacename>@RequestParam</interfacename>'s
|
|
<literal>required</literal> attribute to <literal>false</literal>
|
|
(e.g., <literal>@RequestParam(value="id",
|
|
required="false")</literal>).</para>
|
|
</section>
|
|
|
|
<section id="mvc-ann-requestbody">
|
|
<title>Mapping the request body with the @RequestBody
|
|
annotation</title>
|
|
|
|
<para>The <classname>@RequestBody</classname> method parameter
|
|
annotation indicates that a method parameter should be bound to the
|
|
value of the HTTP request body. For example:</para>
|
|
|
|
<programlisting language="java">@RequestMapping(value = "/something", method = RequestMethod.PUT)
|
|
public void handle(@RequestBody String body, Writer writer) throws IOException {
|
|
writer.write(body);
|
|
}</programlisting>
|
|
|
|
<para>You convert the request body to the method argument by using a
|
|
<interfacename>HttpMessageConverter</interfacename>.
|
|
<interfacename>HttpMessageConverter</interfacename> is responsible for
|
|
converting from the HTTP request message to an object and converting
|
|
from an object to the HTTP response body.
|
|
<classname>DispatcherServlet</classname> supports annotation based
|
|
processing using the
|
|
<classname>DefaultAnnotationHandlerMapping</classname> and
|
|
<classname>AnnotationMethodHandlerAdapter</classname>. In Spring 3.0
|
|
the <classname>AnnotationMethodHandlerAdapter</classname> is extended
|
|
to support the <classname>@RequestBody</classname> and has the
|
|
following <interfacename>HttpMessageConverters</interfacename>
|
|
registered by default:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para><classname>ByteArrayHttpMessageConverter</classname>
|
|
converts byte arrays.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>StringHttpMessageConverter</classname> converts
|
|
strings.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>FormHttpMessageConverter</classname> converts
|
|
form data to/from a MultiValueMap<String, String>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>SourceHttpMessageConverter</classname> converts
|
|
to/from a javax.xml.transform.Source.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>MarshallingHttpMessageConverter</classname>
|
|
converts to/from an object using the
|
|
<classname>org.springframework.oxm</classname> package.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>For more information on these converters, see <link
|
|
linkend="rest-message-conversion">Message Converters</link>.</para>
|
|
|
|
<para>The <classname>MarshallingHttpMessageConverter</classname>
|
|
requires a <interfacename>Marshaller</interfacename> and
|
|
<interfacename>Unmarshaller</interfacename> from the
|
|
<classname>org.springframework.oxm</classname> package to be
|
|
configured on an instance of
|
|
<classname>AnnotationMethodHandlerAdapter</classname> in the
|
|
application context. For example:</para>
|
|
|
|
<programlisting language="xml"><bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
|
|
<property name="messageConverters">
|
|
<util:list id="beanList">
|
|
<ref bean="stringHttpMessageConverter"/>
|
|
<ref bean="marshallingHttpMessageConverter"/>
|
|
</util:list>
|
|
</property
|
|
</bean>
|
|
|
|
<bean id="stringHttpMessageConverter"
|
|
class="org.springframework.http.converter.StringHttpMessageConverter"/>
|
|
|
|
<bean id="marshallingHttpMessageConverter"
|
|
class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter">
|
|
<property name="marshaller" ref="castorMarshaller" />
|
|
<property name="unmarshaller" ref="castorMarshaller" />
|
|
</bean>
|
|
|
|
<bean id="castorMarshaller" class="org.springframework.oxm.castor.CastorMarshaller"/>
|
|
</programlisting>
|
|
</section>
|
|
|
|
<section id="mvc-ann-responsebody">
|
|
<title>Mapping the response body with the @ResponseBody
|
|
annotation</title>
|
|
|
|
<para>The <interfacename>@ResponseBody</interfacename> annotation is
|
|
similar to <interfacename>@RequestBody</interfacename>. This
|
|
annotation can be put on a method <!--Revise *can be put on*. You do *what* with this annotation in regard to a method?-->and
|
|
indicates that the return type should be written straight to the HTTP
|
|
response body (and not placed in a Model, or interpreted as a view
|
|
name). For example:</para>
|
|
|
|
<programlisting language="java">@RequestMapping(value = "/something", method = RequestMethod.PUT)
|
|
@ResponseBody
|
|
public String helloWorld() {
|
|
return "Hello World";
|
|
}</programlisting>
|
|
|
|
<para>The example will result in the text <literal>Hello
|
|
World</literal> being written to the HTTP response stream.</para>
|
|
|
|
<para>As with <interfacename>@RequestBody</interfacename>, Spring converts
|
|
the returned object to a response body by using a
|
|
<interfacename>HttpMessageConverter</interfacename>. For more
|
|
information on these converters, see the previous section and <link
|
|
linkend="rest-message-conversion">Message Converters</link>.</para>
|
|
</section>
|
|
|
|
<section id="mvc-ann-modelattrib">
|
|
<title>Providing a link to data from the model with
|
|
<classname>@ModelAttribute</classname></title>
|
|
|
|
<para><classname>@ModelAttribute</classname> has two usage scenarios
|
|
in controllers. When you map it to <!--is this correct, *map it to*? If not, what do you mean by *is placed on*?-->a
|
|
method parameter, <classname>@ModelAttribute</classname> maps a model
|
|
attribute to the specific, annotated method parameter (see the
|
|
<literal>processSubmit()</literal> method below). This is how the
|
|
controller gets a reference to the object holding the data entered in
|
|
the form.</para>
|
|
|
|
<para>You can also use the <classname>@ModelAttribute </classname>at
|
|
the method level to provide <emphasis>reference data</emphasis> for
|
|
the model (see the <literal>populatePetTypes()</literal> method, as in
|
|
the following example. For this usage the method signature can contain
|
|
the same types as documented previously for the
|
|
<classname>@RequestMapping</classname> annotation.</para>
|
|
|
|
<note>
|
|
<para><classname>@ModelAttribute</classname> annotated methods are
|
|
executed <emphasis>before</emphasis> the chosen
|
|
<classname>@RequestMapping</classname> annotated handler method.
|
|
They effectively pre-populate the implicit model with specific
|
|
attributes, often loaded from a database. Such an attribute can then
|
|
already be accessed through <classname>@ModelAttribute</classname>
|
|
annotated handler method parameters in the chosen handler method,
|
|
potentially with binding and validation applied to it.</para>
|
|
</note>
|
|
|
|
<para>The following code snippet shows these two usages of this
|
|
annotation:</para>
|
|
|
|
<programlisting language="java">@Controller
|
|
@RequestMapping("/owners/{ownerId}/pets/{petId}/edit")
|
|
@SessionAttributes("pet")
|
|
public class EditPetForm {
|
|
|
|
<lineannotation>// ...</lineannotation>
|
|
|
|
<emphasis role="bold">@ModelAttribute("types")</emphasis>
|
|
public Collection<PetType> populatePetTypes() {
|
|
return this.clinic.getPetTypes();
|
|
}
|
|
|
|
@RequestMapping(method = RequestMethod.POST)
|
|
public String processSubmit(
|
|
<emphasis role="bold">@ModelAttribute("pet") Pet pet</emphasis>, BindingResult result, SessionStatus status) {
|
|
|
|
new PetValidator().validate(pet, result);
|
|
if (result.hasErrors()) {
|
|
return "petForm";
|
|
}
|
|
else {
|
|
this.clinic.storePet(pet);
|
|
status.setComplete();
|
|
return "redirect:owner.do?ownerId=" + pet.getOwner().getId();
|
|
}
|
|
}
|
|
|
|
}</programlisting>
|
|
</section>
|
|
|
|
<section id="mvc-ann-sessionattrib">
|
|
<title>Specifying attributes to store in a session with
|
|
<classname>@SessionAttributes</classname></title>
|
|
|
|
<para>The type-level <classname>@SessionAttributes</classname>
|
|
annotation declares session attributes used by a specific handler.
|
|
This will typically list the names of model attributes which should be
|
|
transparently stored in the session or some conversational storage,
|
|
serving as form-backing beans between subsequent requests.</para>
|
|
|
|
<para>The following code snippet shows the usage of this
|
|
annotation:</para>
|
|
|
|
<programlisting language="java">@Controller
|
|
@RequestMapping("/editPet.do")
|
|
<emphasis role="bold">@SessionAttributes("pet")</emphasis>
|
|
public class EditPetForm {
|
|
<lineannotation>// ...</lineannotation>
|
|
}
|
|
</programlisting>
|
|
</section>
|
|
|
|
<section id="mvc-ann-cookievalue">
|
|
<title>Mapping cookie values with the @CookieValue annotation</title>
|
|
|
|
<para>The <interfacename>@CookieValue</interfacename> annotation
|
|
allows a method parameter to be bound to the value of an HTTP
|
|
cookie.</para>
|
|
|
|
<para>Let us consider that the following cookie has been received with
|
|
an http request:</para>
|
|
|
|
<programlisting>JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84</programlisting>
|
|
|
|
<para>The following code sample allows you to easily get the value of
|
|
the "JSESSIONID"cookie:</para>
|
|
|
|
<programlisting language="java">@RequestMapping("/displayHeaderInfo.do")
|
|
public void displayHeaderInfo(<emphasis role="bold">@CookieValue("JSESSIONID")</emphasis> String cookie) {
|
|
|
|
//...
|
|
|
|
}</programlisting>
|
|
|
|
<para>This annotation is supported for annotated handler methods in
|
|
Servlet and Portlet environments.</para>
|
|
</section>
|
|
|
|
<section id="mvc-ann-requestheader">
|
|
<title>Mapping request header attributes with the @RequestHeader
|
|
annotation</title>
|
|
|
|
<para>The <interfacename>@RequestHeader</interfacename> annotation
|
|
allows a method parameter to be bound to a request header.</para>
|
|
|
|
<para>Here is a request header sample:</para>
|
|
|
|
<programlisting>
|
|
Host localhost:8080
|
|
Accept text/html,application/xhtml+xml,application/xml;q=0.9
|
|
Accept-Language fr,en-gb;q=0.7,en;q=0.3
|
|
Accept-Encoding gzip,deflate
|
|
Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
|
|
Keep-Alive 300
|
|
</programlisting>
|
|
|
|
<para>The following code sample allows you to easily get the value of
|
|
the "Accept-Encoding" and "Keep-Alive" headers:</para>
|
|
|
|
<programlisting language="java">@RequestMapping("/displayHeaderInfo.do")
|
|
public void displayHeaderInfo(<emphasis role="bold">@RequestHeader("Accept-Encoding")</emphasis> String encoding,
|
|
<emphasis role="bold">@RequestHeader("Keep-Alive")</emphasis> long keepAlive) {
|
|
|
|
//...
|
|
|
|
}</programlisting>
|
|
|
|
<para>This annotation is supported for annotated handler methods in
|
|
Servlet and Portlet environments.</para>
|
|
</section>
|
|
|
|
<section id="mvc-ann-webdatabinder">
|
|
<title>Customizing <classname>WebDataBinder</classname>
|
|
initialization</title>
|
|
|
|
<para>To customize request parameter binding with PropertyEditors
|
|
through Spring's <classname>WebDataBinder</classname>, you can use
|
|
either <interfacename>@InitBinder</interfacename>-annotated methods
|
|
within your controller or externalize your configuration by providing
|
|
a custom <interfacename>WebBindingInitializer</interfacename>.</para>
|
|
|
|
<section id="mvc-ann-initbinder">
|
|
<title>Customizing data binding with
|
|
<interfacename>@InitBinder</interfacename></title>
|
|
|
|
<para>Annotating controller methods with
|
|
<interfacename>@InitBinder</interfacename> allows you to configure
|
|
web data binding directly within your controller class.
|
|
<interfacename>@InitBinder</interfacename> identifies methods that
|
|
initialize the <classname>WebDataBinder</classname>, which will be
|
|
used to populate command and form object arguments of annotated
|
|
handler methods.</para>
|
|
|
|
<para>Such init-binder methods support all arguments that
|
|
<interfacename>@RequestMapping</interfacename> supports, except for
|
|
command/form objects and corresponding validation result objects.
|
|
Init-binder methods must not have a return value. Thus, they are
|
|
usually declared as <literal>void</literal>. Typical arguments
|
|
include <classname>WebDataBinder</classname> in combination with
|
|
<interfacename>WebRequest</interfacename> or
|
|
<classname>java.util.Locale</classname>, allowing code to register
|
|
context-specific editors.</para>
|
|
|
|
<para>The following example demonstrates the use of
|
|
<interfacename>@InitBinder</interfacename> to configure a
|
|
<classname>CustomDateEditor</classname> for all
|
|
<classname>java.util.Date</classname> form properties.</para>
|
|
|
|
<programlisting language="java">@Controller
|
|
public class MyFormController {
|
|
|
|
<emphasis role="bold">@InitBinder</emphasis>
|
|
public void initBinder(WebDataBinder binder) {
|
|
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
|
|
dateFormat.setLenient(false);
|
|
binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
|
|
}
|
|
|
|
<lineannotation>// ...</lineannotation>
|
|
}</programlisting>
|
|
</section>
|
|
|
|
<section id="mvc-ann-webbindinginitializer">
|
|
<title>Configuring a custom
|
|
<interfacename>WebBindingInitializer</interfacename></title>
|
|
|
|
<para>To externalize data binding initialization, you can provide a
|
|
custom implementation of the
|
|
<interfacename>WebBindingInitializer</interfacename> interface,
|
|
which you then enable by supplying a custom bean configuration for
|
|
an <classname>AnnotationMethodHandlerAdapter</classname>, thus
|
|
overriding the default configuration.</para>
|
|
|
|
<para>The following example from the PetClinic application shows a
|
|
configuration using a custom implementation of the
|
|
<interfacename>WebBindingInitializer</interfacename> interface,
|
|
<classname>org.springframework.samples.petclinic.web.ClinicBindingInitializer</classname>,
|
|
which configures PropertyEditors required by several of the
|
|
PetClinic controllers.</para>
|
|
|
|
<programlisting language="xml"><bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
|
|
<property name="cacheSeconds" value="0" />
|
|
<property name="webBindingInitializer">
|
|
<bean class="org.springframework.samples.petclinic.web.ClinicBindingInitializer" />
|
|
</property>
|
|
</bean>
|
|
</programlisting>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-handlermapping">
|
|
<title>Handler mappings</title>
|
|
|
|
<para>In previous versions of Spring, users were required to define
|
|
<interfacename>HandlerMapping</interfacename>s in the web application
|
|
context to map incoming web requests to appropriate handlers. With the
|
|
introduction of Spring 2.5, <!--IMPORTANT: Shouldn't that say Spring 3.0, since that's upcoming release? If you do mean 2.5, then first sentence should say in pre--><!--2.5 versions of Spring, not *previous*. Also in first sentence, I changed Spring MVC to Spring because it refers to a version.-->the
|
|
<classname>DispatcherServlet</classname> enables the
|
|
<classname>DefaultAnnotationHandlerMapping</classname>, which looks for
|
|
<interfacename>@RequestMapping</interfacename> annotations on
|
|
<interfacename>@Controllers</interfacename>. Typically, you do not need to
|
|
override this default mapping, except when overriding the properties.
|
|
These properties are:</para>
|
|
|
|
<itemizedlist spacing="compact">
|
|
<listitem>
|
|
<para><literal>interceptors</literal>: List of interceptors to use.
|
|
<interfacename>HandlerInterceptor</interfacename>s are discussed in
|
|
<xref linkend="mvc-handlermapping-interceptor" />.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><literal>defaultHandler</literal>: Default handler to use, when
|
|
this handler mapping does not result in a matching handler.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><literal>order</literal>: Based on the value of the order
|
|
property (see the <literal>org.springframework.core.Ordered</literal>
|
|
interface), Spring sorts all handler mappings available in the context
|
|
and applies the first matching handler.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><literal>alwaysUseFullPath</literal>: If
|
|
<literal>true</literal>, Spring uses the full path within the current
|
|
servlet context to find an appropriate handler. If
|
|
<literal>false</literal> (the default), the path within the current
|
|
servlet mapping is used. For example, if a servlet is mapped using
|
|
<literal>/testing/*</literal> and the
|
|
<literal>alwaysUseFullPath</literal> property is set to true,
|
|
<literal>/testing/viewPage.html</literal> is used, whereas if the
|
|
property is set to false, <literal>/viewPage.html</literal> is
|
|
used.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><literal>urlDecode</literal>: Defaults to
|
|
<literal>true</literal>, as of Spring 2.5. <!--OK, or do you mean 3.0?-->If
|
|
you prefer to compare encoded paths, switch this flag to
|
|
<literal>false</literal>. However, the
|
|
<interfacename>HttpServletRequest</interfacename> always exposes the
|
|
servlet path in decoded form. Be aware that the servlet path will not
|
|
match when compared with encoded paths.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><literal>lazyInitHandlers</literal>: Allows lazy initialization
|
|
of <emphasis>singleton</emphasis> handlers (prototype handlers are
|
|
always lazy-initialized). The default value is
|
|
<literal>false</literal>.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para><note>
|
|
<para>The
|
|
<literal>alwaysUseFullPath<literal>,</literal>urlDecode</literal>, and
|
|
<literal>lazyInitHandlers</literal> properties are only available to
|
|
subclasses of
|
|
<interfacename>org.springframework.web.servlet.handler.AbstractUrlHandlerMapping</interfacename>.</para>
|
|
</note></para>
|
|
|
|
<para>The following example shows how to override the default mapping and
|
|
add an interceptor:</para>
|
|
|
|
<programlisting language="xml"><beans>
|
|
<bean id="handlerMapping" class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping">
|
|
<property name="interceptors">
|
|
<bean class="example.MyInterceptor"/>
|
|
</property>
|
|
</bean>
|
|
|
|
<beans></programlisting>
|
|
|
|
<section id="mvc-handlermapping-interceptor">
|
|
<title>Intercepting requests - the
|
|
<interfacename>HandlerInterceptor</interfacename> interface<!--Revise head to delete dash. How should it read? Intercepting requests *through* the HandlerInterceptor Interface? *with*?--></title>
|
|
|
|
<para>Spring's handler mapping mechanism includes handler interceptors,
|
|
which are useful when you want to apply specific functionality to
|
|
certain requests, for example, checking for a principal.</para>
|
|
|
|
<para>Interceptors located in the handler mapping must implement
|
|
<interfacename>HandlerInterceptor</interfacename> from the
|
|
<literal>org.springframework.web.servlet</literal> package. This
|
|
interface defines three methods: one is called
|
|
<emphasis>before</emphasis> the actual handler is executed; one is
|
|
called <emphasis>after</emphasis> the handler is executed; and one is
|
|
called <emphasis>after the complete request has finished</emphasis>.
|
|
<!--I suggest identifying each method in parentheses after the reference to it, in sentence above. -->These
|
|
three methods should provide enough flexibility to do all kinds of
|
|
preprocessing and postprocessing.</para>
|
|
|
|
<para>The <literal>preHandle(..)</literal> method returns a boolean
|
|
value. You can use this method to break or continue the processing of
|
|
the execution chain. When this method returns <literal>true</literal>,
|
|
the handler execution chain will continue, when it returns false, the
|
|
<classname>DispatcherServlet</classname> assumes the interceptor itself
|
|
has taken care of requests (and, for example, rendered an appropriate
|
|
view) and does not continue executing the other interceptors and the
|
|
actual handler in the execution chain.</para>
|
|
|
|
<para>The following example provides an interceptor that intercepts all
|
|
requests and reroutes the user to a specific page if the time is not
|
|
between 9 a.m. and 6 p.m.</para>
|
|
|
|
<programlisting language="xml"><beans>
|
|
<bean id="handlerMapping"
|
|
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
|
|
<property name="interceptors">
|
|
<list>
|
|
<ref bean="officeHoursInterceptor"/>
|
|
</list>
|
|
</property>
|
|
<property name="mappings">
|
|
<value>
|
|
/*.form=editAccountFormController
|
|
/*.view=editAccountFormController
|
|
</value>
|
|
</property>
|
|
</bean>
|
|
|
|
<bean id="officeHoursInterceptor"
|
|
class="samples.TimeBasedAccessInterceptor">
|
|
<property name="openingTime" value="9"/>
|
|
<property name="closingTime" value="18"/>
|
|
</bean>
|
|
<beans></programlisting>
|
|
|
|
<programlisting language="java">package samples;
|
|
|
|
public class TimeBasedAccessInterceptor extends HandlerInterceptorAdapter {
|
|
|
|
private int openingTime;
|
|
private int closingTime;
|
|
|
|
public void setOpeningTime(int openingTime) {
|
|
this.openingTime = openingTime;
|
|
}
|
|
|
|
public void setClosingTime(int closingTime) {
|
|
this.closingTime = closingTime;
|
|
}
|
|
|
|
public boolean preHandle(
|
|
HttpServletRequest request,
|
|
HttpServletResponse response,
|
|
Object handler) throws Exception {
|
|
|
|
Calendar cal = Calendar.getInstance();
|
|
int hour = cal.get(HOUR_OF_DAY);
|
|
if (openingTime <= hour < closingTime) {
|
|
return true;
|
|
} else {
|
|
response.sendRedirect("http://host.com/outsideOfficeHours.html");
|
|
return false;
|
|
}
|
|
}
|
|
}</programlisting>
|
|
|
|
<para>Any request coming in is intercepted by the
|
|
<classname>TimeBasedAccessInterceptor</classname>. If the current time
|
|
is outside office hours, the user is redirected to a static HTML file
|
|
that says, for example, you can only access the website during office
|
|
hours.</para>
|
|
|
|
<para>As you can see, the Spring adapter class
|
|
<classname>HandlerInterceptorAdapter</classname> makes it easier to
|
|
extend the <interfacename>HandlerInterceptor</interfacename>
|
|
interface.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-viewresolver">
|
|
<title>Resolving views</title>
|
|
|
|
<para>All MVC frameworks for web applications provide a way to address
|
|
views. Spring provides view resolvers, which enable you to render models
|
|
in a browser without tying you to a specific view technology. Out of the
|
|
box, Spring enables you to use JSPs, Velocity templates and XSLT views,
|
|
for example. See <xref linkend="view" /> for a discussion of how to
|
|
integrate and use a number of disparate view technologies.</para>
|
|
|
|
<para>The two interfaces that are important to the way Spring handles
|
|
views are <interfacename>ViewResolver</interfacename> and
|
|
<interfacename>View</interfacename>. The
|
|
<interfacename>ViewResolver</interfacename> provides a mapping between
|
|
view names and actual views. The <interfacename>View</interfacename>
|
|
interface addresses the preparation of the request and hands the request
|
|
over to one of the view technologies.</para>
|
|
|
|
<section id="mvc-viewresolver-resolver">
|
|
<title>Resolving views with the
|
|
<interfacename>ViewResolver</interfacename> interface</title>
|
|
|
|
<para>As discussed in <xref linkend="mvc-controller" />, all controllers
|
|
in the Spring Web MVC framework return a
|
|
<classname>ModelAndView</classname> instance. Views in Spring are
|
|
addressed by a view name and are resolved by a view resolver. Spring
|
|
comes with quite a few view resolvers. This table lists most of them; a
|
|
couple of examples follow.</para>
|
|
|
|
<table id="mvc-view-resolvers-tbl">
|
|
<title>View resolvers</title>
|
|
|
|
<tgroup cols="2">
|
|
<colspec colname="c1" colwidth="1*" />
|
|
|
|
<colspec colname="c2" colwidth="2*" />
|
|
|
|
<thead>
|
|
<row>
|
|
<entry><interfacename>ViewResolver</interfacename></entry>
|
|
|
|
<entry>Description</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry><classname>AbstractCachingViewResolver</classname></entry>
|
|
|
|
<entry>Abstract view resolver that caches views. Often views
|
|
need preparation before they can be used; extending this view
|
|
resolver provides caching.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>XmlViewResolver</classname></entry>
|
|
|
|
<entry>Implementation of
|
|
<interfacename>ViewResolver</interfacename> that accepts a
|
|
configuration file written in XML with the same DTD as Spring's
|
|
XML bean factories. The default configuration file is
|
|
<literal>/WEB-INF/views.xml</literal>.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>ResourceBundleViewResolver</classname></entry>
|
|
|
|
<entry>Implementation of
|
|
<interfacename>ViewResolver</interfacename> that uses bean
|
|
definitions in a <classname>ResourceBundle</classname>,
|
|
specified by the bundle base name. Typically you define the
|
|
bundle in a properties file, located in the classpath. <!--Correct to say you define? Seems so, because default implies you can change it.-->The
|
|
default file name is
|
|
<literal>views.properties</literal>.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>UrlBasedViewResolver</classname></entry>
|
|
|
|
<entry>Simple implementation of the
|
|
<interfacename>ViewResolver</interfacename> interface that
|
|
effects the direct resolution of symbolic view names to URLs,
|
|
without an explicit mapping definition. This is appropriate if
|
|
your symbolic names match the names of your view resources in a
|
|
straightforward manner, without the need for arbitrary
|
|
mappings.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>InternalResourceViewResolver</classname></entry>
|
|
|
|
<entry>Convenience subclass of
|
|
<classname>UrlBasedViewResolver</classname> that supports
|
|
<classname>InternalResourceView</classname> (in effect, Servlets
|
|
and JSPs), and subclasses such as
|
|
<classname>JstlView</classname> and
|
|
<classname>TilesView</classname>. You can specify the view class
|
|
for all views generated by this resolver by using
|
|
<literal>setViewClass(..)</literal>. See the Javadocs for the
|
|
<classname>UrlBasedViewResolver</classname> class for
|
|
details.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>VelocityViewResolver</classname> /
|
|
<classname>FreeMarkerViewResolver</classname></entry>
|
|
|
|
<entry>Convenience subclass of
|
|
<classname>UrlBasedViewResolver</classname> that supports
|
|
<classname>VelocityView</classname> (in effect, Velocity
|
|
templates) or <classname>FreeMarkerView</classname>
|
|
,respectively, and custom subclasses of them.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>ContentNegotiatingViewResolver</classname></entry>
|
|
|
|
<entry>Implementation of the
|
|
<interfacename>ViewResolver</interfacename> interface that
|
|
resolves a view based on the request file name or
|
|
<literal>Accept</literal> header. See <xref
|
|
linkend="mvc-multiple-representations" />.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>As an example, with JSP as a view technology, you can use the
|
|
<classname>UrlBasedViewResolver</classname>. This view resolver
|
|
translates a view name to a URL and hands the request over to the
|
|
RequestDispatcher to render the view.</para>
|
|
|
|
<programlisting language="xml"><bean id="viewResolver"
|
|
class="org.springframework.web.servlet.view.UrlBasedViewResolver">
|
|
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
|
|
<property name="prefix" value="/WEB-INF/jsp/"/>
|
|
<property name="suffix" value=".jsp"/>
|
|
</bean></programlisting>
|
|
|
|
<para>When returning <literal>test</literal> as a viewname, this view
|
|
resolver forwards the request to the
|
|
<classname>RequestDispatcher</classname> that will send the request to
|
|
<literal>/WEB-INF/jsp/test.jsp</literal>.</para>
|
|
|
|
<para>When you combine different view technologies in a web application,
|
|
you can use the
|
|
<classname>ResourceBundleViewResolver</classname>:</para>
|
|
|
|
<programlisting language="xml"><bean id="viewResolver"
|
|
class="org.springframework.web.servlet.view.ResourceBundleViewResolver">
|
|
<property name="basename" value="views"/>
|
|
<property name="defaultParentView" value="parentView"/>
|
|
</bean></programlisting>
|
|
|
|
<para>The <classname>ResourceBundleViewResolver</classname> inspects the
|
|
<classname>ResourceBundle</classname> identified by the basename, and
|
|
for each view it is supposed to resolve, it uses the value of the
|
|
property <literal>[viewname].class</literal> as the view class and the
|
|
value of the property <literal>[viewname].url</literal> as the view url.
|
|
As you can see, you can identify a parent view, from which all views in
|
|
the properties file sort of extend. <!--Pls. revise last line. Can you say *extend* instead of *sort of extend*? -->This
|
|
way you can specify a default view class, for example.</para>
|
|
|
|
<note>
|
|
<para>Subclasses of <classname>AbstractCachingViewResolver</classname>
|
|
cache view instances that they resolve. Caching improves performance
|
|
of certain view technologies. It's possible to turn off the cache, by
|
|
setting the <literal>cache</literal> property to
|
|
<literal>false</literal>. Furthermore, if you must refresh a certain
|
|
view at runtime (for example when a Velocity template is modified),
|
|
you can use the <literal>removeFromCache(String viewName, Locale
|
|
loc)</literal> method.</para>
|
|
</note>
|
|
</section>
|
|
|
|
<section id="mvc-viewresolver-chaining">
|
|
<title>Chaining ViewResolvers</title>
|
|
|
|
<para>Spring supports multiple view resolvers. Thus you can chain
|
|
resolvers and, for example, override specific views in certain
|
|
circumstances. You chain view resolvers by adding more than one resolver
|
|
to your application context and, if necessary, by setting the
|
|
<literal>order</literal> property to specify an order. Remember, the
|
|
higher the order property, the later the view resolver is positioned in
|
|
the chain.</para>
|
|
|
|
<para>In the following example, the chain of view resolvers consists of
|
|
two resolvers, a <classname>InternalResourceViewResolver</classname>,
|
|
which is always automatically positioned as the last resolver in the
|
|
chain, and an <classname>XmlViewResolver</classname> for specifying
|
|
Excel views. Excel views are not supported by the
|
|
<classname>InternalResourceViewResolver</classname>.<!--Do you need to say anything else about excel not being supported by one of resolvers? What if anything is the result?--></para>
|
|
|
|
<programlisting language="xml"><bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
|
|
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
|
|
<property name="prefix" value="/WEB-INF/jsp/"/>
|
|
<property name="suffix" value=".jsp"/>
|
|
</bean>
|
|
|
|
<bean id="excelViewResolver" class="org.springframework.web.servlet.view.XmlViewResolver">
|
|
<property name="order" value="1"/>
|
|
<property name="location" value="/WEB-INF/views.xml"/>
|
|
</bean>
|
|
|
|
<lineannotation><!-- in <literal>views.xml</literal> --></lineannotation>
|
|
|
|
<beans>
|
|
<bean name="report" class="org.springframework.example.ReportExcelView"/>
|
|
</beans></programlisting>
|
|
|
|
<para>If a specific view resolver does not result in a view, Spring
|
|
examines the context for other view resolvers. If additional view
|
|
resolvers exist, Spring continues to inspect them. <!--So what happens after Spring inspects them?-->If
|
|
they do not, it throws an <classname>Exception</classname>.</para>
|
|
|
|
<para>The contract of a view resolver specifies that a view resolver
|
|
<emphasis>can</emphasis> return null to indicate the view could not be
|
|
found. Not all view resolvers do this, however, because in some cases,
|
|
the resolver simply cannot detect whether or not the view exists. For
|
|
example, the <classname>InternalResourceViewResolver</classname> uses
|
|
the <classname>RequestDispatcher</classname> internally, and dispatching
|
|
is the only way to figure out if a JSP exists, but this action can only
|
|
execute once. The same holds for the
|
|
<classname>VelocityViewResolver</classname> and some others. Check the
|
|
Javadoc for the view resolver to see whether it reports non-existing
|
|
views. Thus, putting an
|
|
<classname>InternalResourceViewResolver</classname> in the chain in a
|
|
place other than the last, results in the chain not being fully
|
|
inspected, because the
|
|
<classname>InternalResourceViewResolver</classname> will
|
|
<emphasis>always</emphasis> return a view!<!--I don't understand the logic of this. How can it return a view if no view exists or no view can be found? this paragraph is confusing.--><!--Why would you put InternalResourceViewResolver in place other than last? It's automatically last. --></para>
|
|
</section>
|
|
|
|
<section id="mvc-redirecting">
|
|
<title>Redirecting to views<!--Revise to say what you are redirecting to views. OR are you redirecting views? In that case heading should be Redirecting views.--></title>
|
|
|
|
<para>As mentioned previously, a controller typically returns a logical
|
|
view name, which a view resolver resolves to a particular view
|
|
technology. For view technologies such as JSPs that are processed
|
|
through the Servlet or JSP engine, this resolution is usually handled
|
|
through <classname>InternalResourceViewResolver</classname> /
|
|
<classname>InternalResourceView</classname>, which
|
|
issues an internal forward or include, through the Servlet API's
|
|
<literal>RequestDispatcher.forward(..)</literal> or
|
|
<literal>RequestDispatcher.include()</literal>. For other view
|
|
technologies, such as Velocity, XSLT, and so on, the view itself
|
|
produces the content on the response stream.</para>
|
|
|
|
<para>It is sometimes desirable to issue an HTTP redirect back to the
|
|
client, before the view is rendered. This is desirable for example when
|
|
one controller has been called with <literal>POST</literal>ed data, and
|
|
the response is actually a delegation to another controller (for example
|
|
on a successful form submission). In this case, a normal internal
|
|
forward will mean the other controller will also see the same
|
|
<literal>POST</literal> data, which is potentially problematic if it can
|
|
confuse it with other expected data. Another reason to do a redirect
|
|
before displaying the result is that this will eliminate the possibility
|
|
of the user doing a double submission of form data. The browser will
|
|
have sent the initial <literal>POST</literal>, will have seen a redirect
|
|
back and done a subsequent <literal>GET</literal> because of that, and
|
|
thus as far as it is concerned, the current page does not reflect the
|
|
result of a <literal>POST</literal>, but rather of a
|
|
<literal>GET</literal>, so there is no way the user can accidentally
|
|
re-<literal>POST</literal> the same data by doing a refresh. The refresh
|
|
forces a <literal>GET</literal> of the result page, not a resend of the
|
|
initial <literal>POST</literal> data.</para>
|
|
|
|
<section id="mvc-redirecting-redirect-view">
|
|
<title><classname>RedirectView</classname></title>
|
|
|
|
<para>One way to force a redirect as the result of a controller
|
|
response is for the controller to create and return an instance of
|
|
Spring's <classname>RedirectView</classname>. In this case,
|
|
<classname>DispatcherServlet</classname> does not use the normal view
|
|
resolution mechanism. Rather because it has been given the (redirect)
|
|
view already, the <classname>DispatcherServlet</classname> simply
|
|
instructs the view to do its work.</para>
|
|
|
|
<para>The <classname>RedirectView</classname> issues an
|
|
<literal>HttpServletResponse.sendRedirect()</literal> call, which
|
|
comes back to the client browser as an HTTP redirect. <!--Does preceding happen after what happens in first paragraph? Clarify sequence of events.-->All
|
|
model attributes are exposed as HTTP query parameters. This does mean
|
|
that the model must contain only objects (generally Strings or
|
|
convertible to Strings), which can be readily converted to a
|
|
string-form HTTP query parameter.</para>
|
|
|
|
<para>If you use <classname>RedirectView</classname> and the view is
|
|
created by the controller itself, it is recommended that you configure
|
|
the redirect URL to be injected into the controller so that it is not
|
|
baked into the controller but configured in the context along with the
|
|
view names. <!--I revised sentence because it sounds like something you need to do. Also reworded next heading to say what it's about. If not correct,--><!--reword.-->The
|
|
next section discusses this process.</para>
|
|
</section>
|
|
|
|
<section id="mvc-redirecting-redirect-prefix">
|
|
<title>The <literal>redirect:</literal> prefix</title>
|
|
|
|
<para>While the use of <classname>RedirectView</classname> works fine,
|
|
if the controller itself is creating the
|
|
<classname>RedirectView</classname>, there is no getting around the
|
|
fact that the controller is aware that a redirection is happening.
|
|
This is really suboptimal and couples things too tightly. The
|
|
controller should not really care about how the response gets
|
|
handled. In general it should operate only in terms of view names that
|
|
have been injected into it.</para>
|
|
|
|
<para>The special <literal>redirect:</literal> prefix allows you to
|
|
accomplish this. If a view name is returned that has the prefix
|
|
redirect:, then <classname>UrlBasedViewResolver</classname> (and all
|
|
subclasses) recognize this as a special indication that a redirect is
|
|
needed. The rest of the view name will be treated as the redirect
|
|
URL.</para>
|
|
|
|
<para>The net effect is the same as if the controller had returned a
|
|
<classname>RedirectView</classname>, but now the controller itself can
|
|
simply operate in terms of logical view names. A logical view name
|
|
such as <literal>redirect:/my/response/controller.html</literal> will
|
|
redirect relative to the current servlet context, while a name such as
|
|
<literal>redirect:http://myhost.com/some/arbitrary/path.html</literal>
|
|
will redirect to an absolute URL. The important thing is that as long
|
|
as this redirect view name is injected into the controller like any
|
|
other logical view name, the controller is not even aware that
|
|
redirection is happening.</para>
|
|
</section>
|
|
|
|
<section id="mvc-redirecting-forward-prefix">
|
|
<title>The <literal>forward:</literal> prefix<!--Can you revise this heading to say what you're using the forward prefix to accomplish?--></title>
|
|
|
|
<para>It is also possible to use a special <literal>forward:</literal>
|
|
prefix for view names that are ultimately resolved by
|
|
<classname>UrlBasedViewResolver</classname> and subclasses. All this
|
|
does is create an <classname>InternalResourceView</classname> (which
|
|
ultimately does a <literal>RequestDispatcher.forward()</literal>)
|
|
around the rest of the view name, which is considered a URL.
|
|
Therefore, this prefix is not useful with
|
|
<classname>InternalResourceViewResolver</classname> /
|
|
<classname>InternalResourceView</classname> (for JSPs for example).
|
|
But the prefix can be helpful when you are primarily using another
|
|
view technology, but still want to force a forward of a resource to be
|
|
handled by the Servlet/JSP engine. (Note that you may also chain
|
|
multiple view resolvers, instead.)<!--I think the preceding sentences were a bit garbled. I tried to reword a bit. And is this paragraph logical?--></para>
|
|
|
|
<para>As with the <literal>redirect:</literal> prefix, if the view
|
|
name with the prefix is just injected into the controller, the
|
|
controller does not detect that anything special is happening in terms
|
|
of handling the response.<!--Can you reword to clarify the point? The controller does not detect what?--></para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-multiple-representations">
|
|
<title><classname>ContentNegotiatingViewResolver</classname></title>
|
|
|
|
<para>The <classname>ContentNegotiatingViewResolver</classname> does not
|
|
resolve views itself, but rather delegates to other view resolvers,
|
|
selecting the view that resembles the representation requested by the
|
|
client. Two strategies exist for a client to request a representation
|
|
from the server:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Use a distinct URI for each resource,
|
|
typically by using a different file extension in the URI. For
|
|
example, the URI<literal>
|
|
http://www.example.com/users/fred.pdf</literal> requests a PDF
|
|
representation of the user fred, and
|
|
<literal>http://www.example.com/users/fred.xml</literal> requests an
|
|
XML representation.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Use the same URI for the client to locate the resource, but
|
|
set the <literal>Accept</literal> HTTP request header to list the
|
|
<ulink url="http://en.wikipedia.org/wiki/Internet_media_type">media
|
|
types</ulink> that it understands. For example, an HTTP request for
|
|
<literal>http://www.example.com/users/fred</literal> with an
|
|
<literal>Accept</literal> header set to <literal>application/pdf
|
|
</literal>requests a PDF representation of the user fred while
|
|
<literal>http://www.example.com/users/fred</literal> with an
|
|
<literal>Accept</literal> header set to <literal>text/xml</literal>
|
|
requests an XML representation. This strategy is known as <ulink
|
|
url="http://en.wikipedia.org/wiki/Content_negotiation">content
|
|
negotiation</ulink>.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<note>
|
|
<para>One issue with the Accept header is that is impossible to change
|
|
it in a web browser, in HTML. For example, in Firefox, it is fixed
|
|
to<!--So how would you set the Accept header as in second bullet, if you can't do it in html? Indicate?--></para>
|
|
|
|
<programlisting>Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
|
|
</programlisting>
|
|
|
|
<para>For this reason it is common to see the use of a distinct URI
|
|
for each representation.</para>
|
|
</note>
|
|
|
|
<para>To support multiple representations of a resource, Spring provides
|
|
the <classname>ContentNegotiatingViewResolver</classname> to resolve a
|
|
view based on the file extension or <literal>Accept</literal> header of
|
|
the HTTP request. <classname>ContentNegotiatingViewResolver</classname>
|
|
does not perform the view resolution itself, but instead delegates to a
|
|
list of view resolvers that you specify through the bean property
|
|
<literal>ViewResolvers</literal>.<!--A human has to specify this list of resolvers, right? See example below.--></para>
|
|
|
|
<para>The <classname>ContentNegotiatingViewResolver</classname> selects
|
|
an appropriate <classname>View</classname> to handle the request by
|
|
comparing the request media type(s) with the media type (also known as
|
|
<literal>Content-Type</literal>) supported by the
|
|
<classname>View</classname> associated with each of its
|
|
<classname>ViewResolvers</classname>. The first
|
|
<classname>View</classname> in the list that has a compatible
|
|
<literal>Content-Type</literal> returns the representation to the
|
|
client. The <literal>Accept</literal> header may include wildcards, for
|
|
example text/*, in which case a <classname>View</classname> whose
|
|
Context-Type was text/xml is a compatible match.</para>
|
|
|
|
<para>To support the resolution of a view based on a file extension, you
|
|
use the <classname>ContentNegotiatingViewResolver </classname>bean
|
|
property <literal>MediaTypes</literal> to specify a mapping of file
|
|
extensions to media types. For more information on the algorithm to
|
|
determine the request media type, refer to the API documentation for
|
|
<classname>ContentNegotiatingViewResolver</classname>.</para>
|
|
|
|
<para>Here is an example configuration of a
|
|
<classname>ContentNegotiatingViewResolver:</classname></para>
|
|
|
|
<programlisting language="xml"><bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
|
|
<property name="mediaTypes">
|
|
<map>
|
|
<entry key="atom" value="application/atom+xml"/>
|
|
<entry key="html" value="text/html"/>
|
|
</map>
|
|
</property>
|
|
<property name="viewResolvers">
|
|
<list>
|
|
<bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/>
|
|
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
|
|
<property name="prefix" value="/WEB-INF/jsp/"/>
|
|
<property name="suffix" value=".jsp"/>
|
|
</bean>
|
|
</list>
|
|
</property>
|
|
</bean>
|
|
|
|
|
|
<bean id="content" class="com.springsource.samples.rest.SampleContentAtomView"/></programlisting>
|
|
|
|
<para>The <classname>InternalResourceViewResolver</classname> handles
|
|
the translation of view names and JSP pages while the
|
|
<classname>BeanNameViewResolver</classname> returns a view based on the
|
|
name of a bean. (See "<link
|
|
linkend="mvc-viewresolver-resolver">Resolving views with the
|
|
ViewResolver interface</link>" for more details on how Spring looks up
|
|
and instantiates a view.) In this example, the
|
|
<literal>content</literal> bean is a class that inherits from
|
|
<classname>AbstractAtomFeedView</classname>, which returns an Atom RSS
|
|
feed. For more information on creating an Atom Feed representation, see
|
|
the section Atom Views.<!--Need a correct link or x-ref re the preceding sentence.I couldn't find an "Atom Views" section.--></para>
|
|
|
|
<para>In this configuration, if a request is made with an .html
|
|
extension, the view resolver looks for a view that matches the text/html
|
|
media type. The <classname>InternalResourceViewResolver</classname>
|
|
provides the matching view for text/html. If the request is made with
|
|
the file extension .atom, the view resolver looks for a view that
|
|
matches the application/atom+xml media type. This view is provided by
|
|
the <classname>BeanNameViewResolver</classname> that maps to the
|
|
<classname>SampleContentAtomView</classname> if the view name returned
|
|
is <classname>content</classname>. Alternatively, client requests can be
|
|
made without a file extension and setting the Accept header to the
|
|
preferred media-type and the same resolution of request to views would
|
|
occur.<!--Can you reword preceding sentence? I don't follow it.--></para>
|
|
|
|
<note>
|
|
<para>If <classname>ContentNegotiatingViewResolver</classname>'s list
|
|
of ViewResolvers is not configured explicitly, then it automatically
|
|
uses any ViewResolvers defined in the application context.</para>
|
|
</note>
|
|
|
|
<para>The corresponding controller code that returns an Atom RSS feed
|
|
for a URI of the form <literal>http://localhost/content.atom</literal>
|
|
or <literal>http://localhost/content</literal> with an
|
|
<literal>Accept</literal> header of application/atom+xml is shown
|
|
below</para>
|
|
|
|
<programlisting language="java">@Controller
|
|
public class ContentController {
|
|
|
|
private List<SampleContent> contentList = new ArrayList<SampleContent>();
|
|
|
|
@RequestMapping(value="/content", method=RequestMethod.GET)
|
|
public ModelAndView getContent() {
|
|
ModelAndView mav = new ModelAndView();
|
|
mav.setViewName("content");
|
|
mav.addObject("sampleContentList", contentList);
|
|
return mav;
|
|
}
|
|
|
|
}</programlisting>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-localeresolver">
|
|
<title>Using locales</title>
|
|
|
|
<para>Most parts of Spring's architecture support internationalization,
|
|
just as the Spring web MVC framework does.
|
|
<classname>DispatcherServlet</classname> enables you to automatically
|
|
resolve messages using the client's locale. This is done with
|
|
<interfacename>LocaleResolver</interfacename> objects.</para>
|
|
|
|
<para>When a request comes in, the
|
|
<classname>DispatcherServlet</classname> looks for a locale resolver and
|
|
if it finds one it tries to use it to set the locale. Using the
|
|
<literal>RequestContext.getLocale()</literal> method, you can always
|
|
retrieve the locale that was resolved by the locale resolver.</para>
|
|
|
|
<para>Besides the automatic locale resolution, you can also attach an
|
|
interceptor to the handler mapping (see <xref
|
|
linkend="mvc-handlermapping-interceptor" /> for more information on
|
|
handler mapping interceptors), to change the locale under specific
|
|
circumstances, based on a parameter in the request, for example.</para>
|
|
|
|
<para>Locale resolvers and interceptors are all defined in the
|
|
<literal>org.springframework.web.servlet.i18n</literal> package, and are
|
|
configured in your application context in the normal way. Here is a
|
|
selection of the locale resolvers included in Spring.</para>
|
|
|
|
<section id="mvc-localeresolver-acceptheader">
|
|
<title><classname>AcceptHeaderLocaleResolver</classname></title>
|
|
|
|
<para>This locale resolver inspects the
|
|
<literal>accept-language</literal> header in the request that was sent
|
|
by the browser of the client. Usually this header field contains the
|
|
locale of the client's operating system.</para>
|
|
</section>
|
|
|
|
<section id="mvc-localeresolver-cookie">
|
|
<title><classname>CookieLocaleResolver</classname></title>
|
|
|
|
<para>This locale resolver inspects a <classname>Cookie</classname> that
|
|
might exist on the client, to see if a locale is specified. If so, it
|
|
uses that specific locale. Using the properties of this locale resolver,
|
|
you can specify the name of the cookie, as well as the maximum age. Find
|
|
below an example of defining a
|
|
<classname>CookieLocaleResolver</classname>.</para>
|
|
|
|
<programlisting language="xml"><bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver">
|
|
|
|
<property name="cookieName" value="clientlanguage"/>
|
|
|
|
<lineannotation><!-- in seconds. If set to <literal>-1</literal>, the cookie is not persisted (deleted when browser shuts down) --></lineannotation>
|
|
<property name="cookieMaxAge" value="100000">
|
|
|
|
</bean></programlisting>
|
|
|
|
<table id="mvc-cookie-locale-resolver-props-tbl">
|
|
<title><classname>CookieLocaleResolver</classname> properties</title>
|
|
|
|
<tgroup cols="3">
|
|
<colspec colname="c1" colwidth="1*" />
|
|
|
|
<colspec colname="c2" colwidth="1*" />
|
|
|
|
<colspec colname="c3" colwidth="3*" />
|
|
|
|
<thead>
|
|
<row>
|
|
<entry>Property</entry>
|
|
|
|
<entry>Default</entry>
|
|
|
|
<entry>Description</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry>cookieName</entry>
|
|
|
|
<entry>classname + LOCALE</entry>
|
|
|
|
<entry>The name of the cookie</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>cookieMaxAge</entry>
|
|
|
|
<entry>Integer.MAX_INT</entry>
|
|
|
|
<entry>The maximum time a cookie will stay persistent on the
|
|
client. If -1 is specified, the cookie will not be persisted. It
|
|
will only be available until the client shuts down his or her
|
|
browser.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>cookiePath</entry>
|
|
|
|
<entry>/</entry>
|
|
|
|
<entry>Limits the visibility of the cookie to a certain part of
|
|
your site.. When cookiePath is
|
|
specified, the cookie will only be visible to that path, and the
|
|
paths below it.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</section>
|
|
|
|
<section id="mvc-localeresolver-session">
|
|
<title><classname>SessionLocaleResolver</classname></title>
|
|
|
|
<para>The <classname>SessionLocaleResolver</classname> allows you to
|
|
retrieve locales from the session that might be associated with the
|
|
user's request.<!--Aren't you missing some information and example? This section has only one sentence.--></para>
|
|
</section>
|
|
|
|
<section id="mvc-localeresolver-interceptor">
|
|
<title><classname>LocaleChangeInterceptor</classname></title>
|
|
|
|
<para>You can build in changing of locales by adding the
|
|
<classname>LocaleChangeInterceptor</classname> to one of the handler
|
|
mappings (see <xref linkend="mvc-handlermapping" />). It will detect a
|
|
parameter in the request and change the locale. It calls
|
|
<literal>setLocale()</literal> on the
|
|
<interfacename>LocaleResolver</interfacename> that also exists in the
|
|
context. The following example shows that calls to all
|
|
<literal>*.view</literal> resources containing a parameter named
|
|
<literal>siteLanguage</literal> will now change the locale. So, for
|
|
example, a request for the following URL,
|
|
<literal>http://www.sf.net/home.view?siteLanguage=nl</literal> will
|
|
change the site language to Dutch.</para>
|
|
|
|
<programlisting language="xml"><bean id="localeChangeInterceptor"
|
|
class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor">
|
|
<property name="paramName" value="siteLanguage"/>
|
|
</bean>
|
|
|
|
<bean id="localeResolver"
|
|
class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/>
|
|
|
|
<bean id="urlMapping"
|
|
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
|
|
<property name="interceptors">
|
|
<list>
|
|
<ref bean="localeChangeInterceptor"/>
|
|
</list>
|
|
</property>
|
|
<property name="mappings">
|
|
<value>/**/*.view=someController</value>
|
|
</property>
|
|
</bean></programlisting>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-themeresolver">
|
|
<title>Using themes</title>
|
|
|
|
<section id="mvc-themeresolver-introduction">
|
|
<title>Overview of themes</title>
|
|
|
|
<para>You can apply Spring Web MVC framework themes to set the overall look-and-feel
|
|
of your application, thereby enhancing user experience. A theme is a
|
|
collection of static resources, typically style sheets and images, that
|
|
affect the visual style of the application.</para>
|
|
</section>
|
|
|
|
<section id="mvc-themeresolver-defining">
|
|
<title>Defining themes</title>
|
|
|
|
<para>To use themes in your web application, you must set up an implementation of the
|
|
<interfacename>org.springframework.ui.context.ThemeSource</interfacename> interface.
|
|
The <interfacename>WebApplicationContext</interfacename> interface extends
|
|
<interfacename>ThemeSource</interfacename> but delegates its
|
|
responsibilities to a dedicated implementation. By default the delegate
|
|
will be an
|
|
<classname>org.springframework.ui.context.support.ResourceBundleThemeSource</classname>
|
|
implementation that loads properties files from the root of the
|
|
classpath. To use a custom <interfacename>ThemeSource</interfacename>
|
|
implementation or to configure the base name prefix of the
|
|
<classname>ResourceBundleThemeSource</classname>, you can register a
|
|
bean in the application context with the reserved name
|
|
<classname>themeSource</classname>. The web application context
|
|
automatically detects that bean and starts using it.</para>
|
|
|
|
<para>When using the <classname>ResourceBundleThemeSource</classname>, a
|
|
theme is defined in a simple properties file. <!--Revise preceding sentence to clarify: To use ResourceBundleThemeSource, you define a theme in a properties file? OR do you mean a theme--><!--is already defined in a simple properties file for use with ResourceBundleThemeSource?-->The
|
|
properties file lists the resources that make up the theme. Here is an
|
|
example:<!--Is this an example of what a human enters? If not, why is it referred to as an example, if this is exact code already provided?--></para>
|
|
|
|
<programlisting>styleSheet=/themes/cool/style.css
|
|
background=/themes/cool/img/coolBg.jpg</programlisting>
|
|
|
|
<para>The keys of the properties are the names that refer to the themed
|
|
elements from view code. For a JSP, you typically do this using the
|
|
<literal>spring:theme</literal> custom tag, which is very similar to the
|
|
<literal>spring:message</literal> tag. The following JSP fragment uses
|
|
the theme defined in the previous example to customize the look and
|
|
feel:</para>
|
|
|
|
<programlisting language="xml"><%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>
|
|
<html>
|
|
<head>
|
|
<link rel="stylesheet" href="<spring:theme code="styleSheet"/>" type="text/css"/>
|
|
</head>
|
|
<body background="<spring:theme code="background"/>">
|
|
...
|
|
</body>
|
|
</html></programlisting>
|
|
|
|
<para>By default, the <classname>ResourceBundleThemeSource</classname>
|
|
uses an empty base name prefix. As a result, the properties files are
|
|
loaded from the root of the classpath, so you would put the
|
|
<literal>cool.properties</literal> theme definition in a directory at
|
|
the root of the classpath, for example, in
|
|
<literal>/WEB-INF/classes</literal>. The
|
|
<classname>ResourceBundleThemeSource</classname> uses the standard Java
|
|
resource bundle loading mechanism, allowing for full
|
|
internationalization of themes. For example, we could have a
|
|
<literal>/WEB-INF/classes/cool_nl.properties</literal> that references a
|
|
special background image with Dutch text on it.</para>
|
|
</section>
|
|
|
|
<section id="mvc-themeresolver-resolving">
|
|
<title>Theme resolvers</title>
|
|
|
|
<para>After you define themes, as in the preceding section, you decide
|
|
which theme to use. The <classname>DispatcherServlet</classname> will
|
|
look for a bean named <classname>themeResolver</classname> to find out
|
|
which <interfacename>ThemeResolver</interfacename> implementation to
|
|
use. A theme resolver works in much the same way as a
|
|
<interfacename>LocaleResolver</interfacename>. It detects the theme to
|
|
use for a particular request and can also alter the request's theme. The
|
|
following theme resolvers are provided by Spring:</para>
|
|
|
|
<table id="mvc-theme-resolver-impls-tbl">
|
|
<title><interfacename>ThemeResolver</interfacename>
|
|
implementations</title>
|
|
|
|
<tgroup cols="2">
|
|
<colspec colname="c1" colwidth="1*" />
|
|
|
|
<colspec colname="c3" colwidth="3*" />
|
|
|
|
<thead>
|
|
<row>
|
|
<entry>Class</entry>
|
|
|
|
<entry>Description</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry><classname>FixedThemeResolver</classname></entry>
|
|
|
|
<entry>Selects a fixed theme, set using the
|
|
<classname>defaultThemeName</classname> property.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>SessionThemeResolver</classname></entry>
|
|
|
|
<entry>The theme is maintained in the user's HTTP session. It
|
|
only needs to be set once for each session, but is not persisted
|
|
between sessions.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>CookieThemeResolver</classname></entry>
|
|
|
|
<entry>The selected theme is stored in a cookie on the
|
|
user-agent's machine.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>Spring also provides a
|
|
<classname>ThemeChangeInterceptor</classname>, which allows theme
|
|
changes on every request with a simple request parameter.<!--Do you need more info or an example re preceding sentence?--></para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-multipart">
|
|
<title>Spring's multipart (fileupload) support</title>
|
|
|
|
<section id="mvc-multipart-introduction">
|
|
<title>Introduction</title>
|
|
|
|
<para>Spring's built-in multipart support handles file uploads in web
|
|
applications. You enable this multipart support with pluggable
|
|
<interfacename>MultipartResolver</interfacename> objects, defined in the
|
|
<literal>org.springframework.web.multipart</literal> package. <!--I reworded preceding because next paragraph indicates that *you* have to enable; spring does not do multipart handling by default.--><!--Do you mean *you* use pluggable objects to configure mulitpart? Or Spring has accomplished this already?-->Out
|
|
of the box, Spring provides a
|
|
<interfacename>MultipartResolver</interfacename> for use with
|
|
<emphasis>Commons FileUpload</emphasis> (<ulink
|
|
url="http://jakarta.apache.org/commons/fileupload"></ulink>). <!--pdf shows link to apache.org but here it looks blank (although tagged as ulink). Is this link ok?-->How
|
|
uploading files is supported will be described in the rest of this
|
|
chapter.</para>
|
|
|
|
<para>By default, Spring does no multipart handling, because some
|
|
developers want to handle multiparts themselves. You enable Spring
|
|
multipart handling by adding a multipart resolver to the web
|
|
application's context. Each request is inspected to see if it contains a
|
|
multipart. If no multipart is found, the request continues as expected.
|
|
If a multipart is found in the request, the
|
|
<classname>MultipartResolver</classname> that has been declared in your
|
|
context is used. After that, the multipart attribute in your request is
|
|
treated like any other attribute.</para>
|
|
</section>
|
|
|
|
<section id="mvc-multipart-resolver">
|
|
<title>Using the
|
|
<interfacename>MultipartResolver</interfacename></title>
|
|
|
|
<para>The following example shows how to use the
|
|
<classname>CommonsMultipartResolver</classname>:</para>
|
|
|
|
<programlisting language="xml"><bean id="multipartResolver"
|
|
class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
|
|
|
|
<lineannotation><!-- one of the properties available; the maximum file size in bytes --></lineannotation>
|
|
<property name="maxUploadSize" value="100000"/>
|
|
</bean></programlisting>
|
|
|
|
<para>This example uses the
|
|
<classname>CosMultipartResolver</classname>:</para>
|
|
|
|
<programlisting language="xml"><bean id="multipartResolver" class="org.springframework.web.multipart.cos.CosMultipartResolver">
|
|
|
|
<lineannotation><!-- one of the properties available; the maximum file size in bytes --></lineannotation>
|
|
<property name="maxUploadSize" value="100000"/>
|
|
</bean></programlisting>
|
|
|
|
<para>Of course you also need to put the appropriate jars in your
|
|
classpath for the multipart resolver to work. In the case of the
|
|
<classname>CommonsMultipartResolver</classname>, you need to use
|
|
<literal>commons-fileupload.jar</literal>; in the case of the
|
|
<classname>CosMultipartResolver</classname>, use
|
|
<literal>cos.jar</literal>.</para>
|
|
|
|
<para>When the Spring <classname>DispatcherServlet</classname> detects a
|
|
multi-part request, it activates the resolver that has been declared in
|
|
your context and hands over the request. The resolver then wraps the
|
|
current <classname>HttpServletRequest</classname> into a
|
|
<classname>MultipartHttpServletRequest</classname> that supports
|
|
multipart file uploads. Using the
|
|
<classname>MultipartHttpServletRequest</classname> you can get
|
|
information about the multiparts contained by this request and actually
|
|
get access to the multipart files themselves in your controllers.</para>
|
|
</section>
|
|
|
|
<section id="mvc-multipart-forms">
|
|
<title>Handling a file upload in a form</title>
|
|
|
|
<para>After the <classname>MultipartResolver</classname> completes its
|
|
job, the request is processed like any other. To use it<!--to use what?-->,
|
|
you create a form with an upload field (see immediately below) that will
|
|
allow the user to upload a form, then let Spring bind the file onto your
|
|
form (backing object). <!--I reworded because it sounded like you refer twice to creating a form. Where in example do you *let* Spring bind the file? Clarify.--><!--Does reader know what a backing object refers to?--></para>
|
|
|
|
<programlisting language="xml"><html>
|
|
<head>
|
|
<title>Upload a file please</title>
|
|
</head>
|
|
<body>
|
|
<h1>Please upload a file</h1>
|
|
<form method="post" action="upload.form" enctype="multipart/form-data">
|
|
<input type="file" name="file"/>
|
|
<input type="submit"/>
|
|
</form>
|
|
</body>
|
|
</html></programlisting>
|
|
|
|
<para>As you can see, we've created a field named after the property of
|
|
the bean that holds the <literal>byte[]</literal>. <!--Preceding sentence: no, byte [] is not shown in preceding example.-->The
|
|
encoding attribute (<literal>enctype="multipart/form-data"</literal>)
|
|
lets the browser know how to encode the multipart fields.</para>
|
|
|
|
<para>As with any property that is not automatically <!--changed from *automagically*!-->convertible
|
|
to a string or primitive type, you must register a custom editor with
|
|
the <classname>ServletRequestDatabinder</classname> to be able to put
|
|
binary data in your objects. Two editors can handle files and set the
|
|
results on an object. A <classname>StringMultipartEditor</classname> can
|
|
convert files to Strings (using a user-defined character set), and a
|
|
<classname>ByteArrayMultipartEditor</classname> converts files to byte
|
|
arrays. They function just as the
|
|
<classname>CustomDateEditor</classname> does.</para>
|
|
|
|
<para>So, to be able to upload files using an HTML form, declare the
|
|
resolver, a url mapping to a controller that will process the bean, and
|
|
the controller itself:</para>
|
|
|
|
<programlisting language="xml"><beans>
|
|
<lineannotation><!-- lets use the Commons-based implementation of the MultipartResolver interface --></lineannotation>
|
|
<bean id="multipartResolver"
|
|
class="org.springframework.web.multipart.commons.CommonsMultipartResolver"/>
|
|
|
|
<bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
|
|
<property name="mappings">
|
|
<value>
|
|
/upload.form=fileUploadController
|
|
</value>
|
|
</property>
|
|
</bean>
|
|
|
|
<bean id="fileUploadController" class="examples.FileUploadController">
|
|
<property name="commandClass" value="examples.FileUploadBean"/>
|
|
<property name="formView" value="fileuploadform"/>
|
|
<property name="successView" value="confirmation"/>
|
|
</bean>
|
|
|
|
</beans></programlisting>
|
|
|
|
<para>After that, create the controller and the actual class to hold the
|
|
file property:<!--Indicate which editor you're using (ByteArray etc.) and what it's doing.--></para>
|
|
|
|
<programlisting language="java">public class FileUploadController extends SimpleFormController {
|
|
|
|
protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response,
|
|
Object command, BindException errors) throws ServletException, IOException {
|
|
|
|
<lineannotation> // cast the bean</lineannotation>
|
|
FileUploadBean bean = (FileUploadBean) command;
|
|
|
|
<lineannotation> let's see if there's content there</lineannotation>
|
|
byte[] file = bean.getFile();
|
|
if (file == null) {
|
|
<lineannotation> // hmm, that's strange, the user did not upload anything</lineannotation>
|
|
}
|
|
|
|
<lineannotation> // well, let's do nothing with the bean for now and return</lineannotation>
|
|
return super.onSubmit(request, response, command, errors);
|
|
}
|
|
|
|
protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder)
|
|
throws ServletException {
|
|
// to actually be able to convert Multipart instance to byte[]
|
|
// we have to register a custom editor
|
|
binder.registerCustomEditor(byte[].class, new ByteArrayMultipartFileEditor());
|
|
// now Spring knows how to handle multipart object and convert them
|
|
}
|
|
}
|
|
|
|
public class FileUploadBean {
|
|
|
|
private byte[] file;
|
|
|
|
public void setFile(byte[] file) {
|
|
this.file = file;
|
|
}
|
|
|
|
public byte[] getFile() {
|
|
return file;
|
|
}
|
|
}</programlisting>
|
|
|
|
<para>As you can see, the <classname>FileUploadBean</classname> has a
|
|
property typed <literal>byte[]</literal> that holds the file. The
|
|
controller registers a custom editor to let Spring know how to convert
|
|
the multipart objects the resolver has found to properties specified by
|
|
the bean. In this example, nothing is done with the
|
|
<literal>byte[]</literal> property of the bean itself, but in practice
|
|
you can do save it in a database, mail it to somebody, and so on.</para>
|
|
|
|
<para>The following is an equivalent example in which a file is bound
|
|
straight to a String-typed property on a (form backing) object:<!--mention editor and its role.--></para>
|
|
|
|
<programlisting language="java">public class FileUploadController extends SimpleFormController {
|
|
|
|
protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response,
|
|
Object command, BindException errors) throws ServletException, IOException {
|
|
|
|
<lineannotation> // cast the bean</lineannotation>
|
|
FileUploadBean bean = (FileUploadBean) command;
|
|
|
|
<lineannotation> let's see if there's content there</lineannotation>
|
|
String file = bean.getFile();
|
|
if (file == null) {
|
|
<lineannotation> // hmm, that's strange, the user did not upload anything</lineannotation>
|
|
}
|
|
|
|
<lineannotation> // well, let's do nothing with the bean for now and return</lineannotation>
|
|
return super.onSubmit(request, response, command, errors);
|
|
}
|
|
|
|
protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder)
|
|
throws ServletException {
|
|
// to actually be able to convert Multipart instance to a String
|
|
// we have to register a custom editor
|
|
binder.registerCustomEditor(String.class, new StringMultipartFileEditor());
|
|
// now Spring knows how to handle multipart object and convert them
|
|
}
|
|
|
|
}
|
|
|
|
public class FileUploadBean {
|
|
|
|
private String file;
|
|
|
|
public void setFile(String file) {
|
|
this.file = file;
|
|
}
|
|
|
|
public String getFile() {
|
|
return file;
|
|
}
|
|
}</programlisting>
|
|
|
|
<para>The preceding example only makes (logical) sense in the context of
|
|
uploading a plain text file. It would not work as well with an image
|
|
file upload.</para>
|
|
|
|
<para>The third (and final) option is where one binds directly to a
|
|
<interfacename>MultipartFile</interfacename> property declared on the
|
|
(form backing) object's class. In this case one does not need to
|
|
register any custom <interfacename>PropertyEditor</interfacename>
|
|
because there is no type conversion to be performed.</para>
|
|
|
|
<programlisting language="java">public class FileUploadController extends SimpleFormController {
|
|
|
|
protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response,
|
|
Object command, BindException errors) throws ServletException, IOException {
|
|
|
|
<lineannotation> // cast the bean</lineannotation>
|
|
FileUploadBean bean = (FileUploadBean) command;
|
|
|
|
<lineannotation> let's see if there's content there</lineannotation>
|
|
MultipartFile file = bean.getFile();
|
|
if (file == null) {
|
|
<lineannotation> // hmm, that's strange, the user did not upload anything</lineannotation>
|
|
}
|
|
|
|
<lineannotation> // well, let's do nothing with the bean for now and return</lineannotation>
|
|
return super.onSubmit(request, response, command, errors);
|
|
}
|
|
}
|
|
|
|
public class FileUploadBean {
|
|
|
|
private MultipartFile file;
|
|
|
|
public void setFile(MultipartFile file) {
|
|
this.file = file;
|
|
}
|
|
|
|
public MultipartFile getFile() {
|
|
return file;
|
|
}
|
|
}</programlisting>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-exceptionhandlers">
|
|
<title>Handling exceptions</title>
|
|
|
|
<section>
|
|
<title
|
|
id="mvc-HandlerExceptionResolver"><interfacename>HandlerExceptionResolver<!--I thought HandlerExceptionResolver needed its own section.--></interfacename></title>
|
|
|
|
<para>Spring <literal>HandlerExceptionResolvers</literal> ease the pain
|
|
of unexpected exceptions that occur while your request is handled by a
|
|
controller that matched the request.
|
|
<literal>HandlerExceptionResolvers</literal> somewhat resemble the
|
|
exception mappings you can define in the web application descriptor
|
|
<literal>web.xml</literal>. However, they provide a more flexible way to
|
|
handle exceptions. They provide information about which handler was
|
|
executing when the exception was thrown. Furthermore, a programmatic way
|
|
of handling exception gives you more options for responding
|
|
appropriately before the request is forwarded to another URL (the same
|
|
end result as when you use the servlet specific exception
|
|
mappings).</para>
|
|
|
|
<para>Besides implementing the
|
|
<interfacename>HandlerExceptionResolver</interfacename> interface, which
|
|
is only a matter of implementing the
|
|
<literal>resolveException(Exception, Handler)</literal> method and
|
|
returning a <classname>ModelAndView</classname>, you may also use the
|
|
<classname>SimpleMappingExceptionResolver</classname>. This resolver
|
|
enables you to take the class name of any exception that might be thrown
|
|
and map it to a view name. This is functionally equivalent to the
|
|
exception mapping feature from the Servlet API, but it is also possible
|
|
to implement more finely grained mappings of exceptions from different
|
|
handlers.</para>
|
|
</section>
|
|
|
|
<section id="mvc-ann-exceptionhandler">
|
|
<title><interfacename>@ExceptionHandler<!--Changed this from @ExceptionResolver because text and example say @ExceptionHandler.--></interfacename></title>
|
|
|
|
<para>An alternative to the
|
|
<interfacename>HandlerExceptionResolver</interfacename> interface is the
|
|
<interfacename>@ExceptionHandler</interfacename> annotation. You use the
|
|
<classname>@ExceptionHandler</classname> method annotation within a
|
|
controller to specify which method is invoked when an exception of a
|
|
specific type is thrown during the execution of controller methods. For
|
|
example:</para>
|
|
|
|
<programlisting language="java">@Controller
|
|
public class SimpleController {
|
|
|
|
// other controller method omitted
|
|
|
|
@ExceptionHandler(IOException.class)
|
|
public String handleIOException(IOException ex, HttpServletRequest request) {
|
|
return ClassUtils.getShortName(ex.getClass());
|
|
}
|
|
}</programlisting>
|
|
|
|
<para>will invoke the 'handlerIOException' method when a
|
|
<classname>java.io.IOException</classname> is thrown.</para>
|
|
|
|
<para>The <classname>@ExceptionHandler</classname> value can be set to
|
|
an array of Exception types. If an exception is thrown matches one of
|
|
the types in the list, then the method annotated with the matching
|
|
<classname>@ExceptionHandler</classname> will be invoked. If the
|
|
annotation value is not set then the exception types listed as method
|
|
arguments are used.</para>
|
|
|
|
<para>Much like standard controller methods annotated with a
|
|
<classname>@RequestMapping</classname> annotation, the method arguments
|
|
and return values of <classname>@ExceptionHandler</classname> methods
|
|
are very flexible. For example, the
|
|
<classname>HttpServletRequest</classname> can be accessed in Servlet
|
|
environments and the <classname>PortletRequest</classname> in Portlet
|
|
environments. The return type can be a <classname>String</classname>,
|
|
which is interpreted as a view name or a
|
|
<classname>ModelAndView</classname> object. Refer to the API
|
|
documentation for more details.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-coc">
|
|
<title>Convention over configuration support</title>
|
|
|
|
<para>For a lot of projects, sticking to established conventions and
|
|
having reasonable defaults is just what they (the projects) need... this
|
|
theme of convention-over-configuration now has explicit support in Spring
|
|
Web MVC. What this means is that if you establish a set of naming
|
|
conventions and suchlike, you can <emphasis>substantially</emphasis> cut
|
|
down on the amount of configuration that is required to set up handler
|
|
mappings, view resolvers, <classname>ModelAndView</classname> instances,
|
|
etc. This is a great boon with regards to rapid prototyping, and can also
|
|
lend a degree of (always good-to-have) consistency across a codebase
|
|
should you choose to move forward with it into production.</para>
|
|
|
|
<para>Convention-over-configuration support addresses the three core areas
|
|
of MVC -- models, views, and controllers.</para>
|
|
|
|
<section id="mvc-coc-ccnhm">
|
|
<title>The Controller
|
|
<classname>ControllerClassNameHandlerMapping</classname></title>
|
|
|
|
<para>The <classname>ControllerClassNameHandlerMapping</classname> class
|
|
is a <interfacename>HandlerMapping</interfacename> implementation that
|
|
uses a convention to determine the mapping between request URLs and the
|
|
<interfacename>Controller</interfacename> instances that are to handle
|
|
those requests.</para>
|
|
|
|
<para>Consider the following simple
|
|
<interfacename>Controller</interfacename> implementation. Take special
|
|
notice of the <emphasis>name</emphasis> of the class.<!--Re preceding sentence, I don't see where the name of the class is discussed in explanation following the example. See my next comment.--></para>
|
|
|
|
<programlisting language="java">public class <emphasis role="bold">ViewShoppingCartController</emphasis> implements Controller {
|
|
|
|
public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
|
|
<lineannotation>// the implementation is not hugely important for this example...</lineannotation>
|
|
}
|
|
}</programlisting>
|
|
|
|
<para>Here is a snippet from the attendent Spring Web MVC configuration
|
|
file...</para>
|
|
|
|
<programlisting language="xml"><bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/>
|
|
|
|
<bean id="<emphasis role="bold">viewShoppingCart</emphasis>" class="x.y.z.ViewShoppingCartController">
|
|
<lineannotation><!-- inject dependencies as required... --></lineannotation>
|
|
</bean></programlisting>
|
|
|
|
<para>The <classname>ControllerClassNameHandlerMapping</classname> finds
|
|
all of the various handler (or
|
|
<interfacename>Controller</interfacename>) beans defined in its
|
|
application context and strips <literal>Controller</literal> off the
|
|
name to define its handler mappings. Thus,
|
|
<classname>ViewShoppingCartController</classname> maps to the
|
|
<literal>/viewshoppingcart*</literal> request URL.</para>
|
|
|
|
<para>Let's look at some more examples so that the central idea becomes
|
|
immediately familiar. (Notice all lowercase in the URLs, in contrast to
|
|
camel-cased <interfacename>Controller</interfacename> class
|
|
names.)</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para><classname>WelcomeController</classname> maps to the
|
|
<literal>/welcome*</literal> request URL</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>HomeController</classname> maps to the
|
|
<literal>/home*</literal> request URL</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>IndexController</classname> maps to the
|
|
<literal>/index*</literal> request URL</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>RegisterController</classname> maps to the
|
|
<literal>/register*</literal> request URL</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>In the case of <classname>MultiActionController</classname>
|
|
handler classes, the mappings generated are slightly more complex. The
|
|
<interfacename>Controller</interfacename> names in the following
|
|
examples are assumed to be <classname>MultiActionController</classname>
|
|
implementations:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para><classname>AdminController</classname> maps to the
|
|
<literal>/admin<emphasis role="bold">/*</emphasis></literal> request
|
|
URL</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>CatalogController</classname> maps to the
|
|
<literal>/catalog<emphasis role="bold">/*</emphasis></literal>
|
|
request URL</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>If you follow the convention of naming your
|
|
<interfacename>Controller</interfacename> implementations as
|
|
<literal>xxx<emphasis role="bold">Controller</emphasis></literal>, the
|
|
<classname>ControllerClassNameHandlerMapping</classname> saves you the
|
|
tedium of defining and maintaining a potentially
|
|
<emphasis>looooong</emphasis>
|
|
<classname>SimpleUrlHandlerMapping</classname> (or suchlike).</para>
|
|
|
|
<para>The <classname>ControllerClassNameHandlerMapping</classname> class
|
|
extends the <classname>AbstractHandlerMapping</classname> base class so
|
|
you can define <interfacename>HandlerInterceptor</interfacename>
|
|
instances and everything else just as you would with many other
|
|
<interfacename>HandlerMapping</interfacename> implementations.</para>
|
|
</section>
|
|
|
|
<section id="mvc-coc-modelmap">
|
|
<title>The Model <classname>ModelMap</classname>
|
|
(<classname>ModelAndView</classname>)</title>
|
|
|
|
<para>The <classname>ModelMap</classname> class is essentially a
|
|
glorified <interfacename>Map</interfacename> that can make adding
|
|
objects that are to be displayed in (or on) a
|
|
<interfacename>View</interfacename> adhere to a common naming
|
|
convention. Consider the following
|
|
<interfacename>Controller</interfacename> implementation; notice that
|
|
objects are added to the <classname>ModelAndView</classname> without any
|
|
associated name specified.</para>
|
|
|
|
<programlisting language="java">public class DisplayShoppingCartController implements Controller {
|
|
|
|
public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
|
|
|
|
List cartItems = <lineannotation>// get a <interfacename>List</interfacename> of <classname>CartItem</classname> objects</lineannotation>
|
|
User user = <lineannotation>// get the <classname>User</classname> doing the shopping</lineannotation>
|
|
|
|
ModelAndView mav = new ModelAndView("displayShoppingCart"); <lineannotation><-- the logical view name</lineannotation>
|
|
|
|
mav.addObject(cartItems); <lineannotation><-- look ma, no name, just the object</lineannotation>
|
|
mav.addObject(user); <lineannotation><-- and again ma!</lineannotation>
|
|
|
|
return mav;
|
|
}
|
|
}</programlisting>
|
|
|
|
<para>The <classname>ModelAndView</classname> class uses a
|
|
<classname>ModelMap</classname> class that is a custom
|
|
<interfacename>Map</interfacename> implementation that automatically
|
|
generates a key for an object when an object is added to it. The
|
|
strategy for determining the name for an added object is, in the case of
|
|
a scalar object such as <classname>User</classname>, to use the short
|
|
class name of the object's class. The following examples are names that
|
|
are generated for scalar objects put into a
|
|
<classname>ModelMap</classname> instance.</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>An <classname>x.y.User</classname> instance added will have
|
|
the name <literal>user</literal> generated.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>An <classname>x.y.Registration</classname> instance added will
|
|
have the name <literal>registration</literal> generated.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>An <classname>x.y.Foo</classname> instance added will have the
|
|
name <literal>foo</literal> generated.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>A <classname>java.util.HashMap</classname> instance added will
|
|
have the name <literal>hashMap</literal> generated. You probably
|
|
want to be explicit about the name in this case because
|
|
<literal>hashMap</literal> is less than intuitive.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Adding <literal>null</literal> will result in an
|
|
<classname>IllegalArgumentException</classname> being thrown. If the
|
|
object (or objects) that you are adding could be
|
|
<literal>null</literal>, then you will also want to be explicit
|
|
about the name.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<sidebar>
|
|
<title>What, no automatic pluralisation?</title>
|
|
|
|
<para>Spring Web MVC's convention-over-configuration support does not
|
|
support automatic pluralisation. That is, you cannot add a
|
|
<interfacename>List</interfacename> of <classname>Person</classname>
|
|
objects to a <classname>ModelAndView</classname> and have the
|
|
generated name be <classname>people</classname>.</para>
|
|
|
|
<para>This decision was made after some debate, with the
|
|
<quote>Principle of Least Surprise</quote> winning out in the
|
|
end.</para>
|
|
</sidebar>
|
|
|
|
<para>The strategy for generating a name after adding a
|
|
<interfacename>Set</interfacename>, <interfacename>List</interfacename>
|
|
or array object is to peek into the collection, take the short class
|
|
name of the first object in the collection, and use that with
|
|
<literal>List</literal> appended to the name. Some examples will make
|
|
the semantics of name generation for collections clearer...</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>An <classname>x.y.User[]</classname> array with one or more
|
|
<classname>x.y.User</classname> elements added will have the name
|
|
<literal>userList</literal> generated.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>An <classname>x.y.Foo[]</classname> array with one or more
|
|
<classname>x.y.User</classname> elements added will have the name
|
|
<literal>fooList</literal> generated.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>A <classname>java.util.ArrayList</classname> with one or more
|
|
<classname>x.y.User</classname> elements added will have the name
|
|
<literal>userList</literal> generated.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>A <classname>java.util.HashSet</classname> with one or more
|
|
<classname>x.y.Foo</classname> elements added will have the name
|
|
<literal>fooList</literal> generated.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>An <emphasis role="bold">empty</emphasis>
|
|
<classname>java.util.ArrayList</classname> will not be added at all
|
|
(in effect, the <methodname>addObject(..)</methodname> call will
|
|
essentially be a no-op).</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
|
|
<section id="mvc-coc-r2vnt">
|
|
<title>The View -
|
|
<interfacename>RequestToViewNameTranslator</interfacename></title>
|
|
|
|
<para>The <interfacename>RequestToViewNameTranslator</interfacename>
|
|
interface determines a logical <interfacename>View</interfacename> name
|
|
when no such logical view name is explicitly supplied. It has just one
|
|
implementation, the
|
|
<classname>DefaultRequestToViewNameTranslator</classname> class.</para>
|
|
|
|
<para>The <classname>DefaultRequestToViewNameTranslator</classname> maps
|
|
request URLs to logical view names, as with this example:</para>
|
|
|
|
<programlisting language="java">public class RegistrationController implements Controller {
|
|
|
|
public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
|
|
<lineannotation>// process the request...</lineannotation>
|
|
ModelAndView mav = new ModelAndView();
|
|
<lineannotation>// add <emphasis role="bold">data</emphasis> as necessary to the model...</lineannotation>
|
|
return mav;
|
|
<lineannotation>// notice that no <interfacename>View</interfacename> or logical view name has been set</lineannotation>
|
|
}
|
|
}</programlisting>
|
|
|
|
<programlisting language="xml"><?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN"
|
|
"http://www.springframework.org/dtd/spring-beans-2.0.dtd">
|
|
<beans>
|
|
|
|
<lineannotation><!-- this bean with the well known name generates view names for us --></lineannotation>
|
|
<bean id="viewNameTranslator" class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/>
|
|
|
|
<bean class="x.y.RegistrationController">
|
|
<lineannotation><!-- inject dependencies as necessary --></lineannotation>
|
|
</bean>
|
|
|
|
<lineannotation><!-- maps request URLs to Controller names --></lineannotation>
|
|
<bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/>
|
|
|
|
<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
|
|
<property name="prefix" value="/WEB-INF/jsp/"/>
|
|
<property name="suffix" value=".jsp"/>
|
|
</bean>
|
|
|
|
</beans>
|
|
</programlisting>
|
|
|
|
<para>Notice how in the implementation of the
|
|
<literal>handleRequest(..)</literal> method no
|
|
<interfacename>View</interfacename> or logical view name is ever set on
|
|
the <classname>ModelAndView</classname> that is returned. The
|
|
<classname>DefaultRequestToViewNameTranslator</classname> is tasked with
|
|
generating a <emphasis>logical view name</emphasis> from the URL of the
|
|
request. In the case of the above
|
|
<classname>RegistrationController</classname>, which is used in
|
|
conjunction with the
|
|
<classname>ControllerClassNameHandlerMapping</classname>, a request URL
|
|
of <literal>http://localhost/registration.html</literal> results in a
|
|
logical view name of <literal>registration</literal> being generated by
|
|
the <classname>DefaultRequestToViewNameTranslator</classname>. This
|
|
logical view name is then resolved into the
|
|
<literal>/WEB-INF/jsp/registration.jsp</literal> view by the
|
|
<classname>InternalResourceViewResolver</classname> bean.</para>
|
|
|
|
<tip>
|
|
<para>You do not need to define a
|
|
<classname>DefaultRequestToViewNameTranslator</classname> bean
|
|
explicitly. If you like the default settings of the
|
|
<classname>DefaultRequestToViewNameTranslator</classname>, you can
|
|
rely on the Spring Web MVC <classname>DispatcherServlet</classname> to
|
|
instantiate an instance of this class if one is not explicitly
|
|
configured.</para>
|
|
</tip>
|
|
|
|
<para>Of course, if you need to change the default settings, then you do
|
|
need to configure your own
|
|
<classname>DefaultRequestToViewNameTranslator</classname> bean
|
|
explicitly. Consult the comprehensive Javadoc for the
|
|
<classname>DefaultRequestToViewNameTranslator</classname> class for
|
|
details of the various properties that can be configured.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-etag">
|
|
<title>ETag support</title>
|
|
|
|
<para>An <ulink url="http://en.wikipedia.org/wiki/HTTP_ETag">ETag</ulink>
|
|
(entity tag) is an HTTP response header returned by an HTTP/1.1 compliant
|
|
web server used to determine change in content at a given URL. It can be
|
|
considered to be the more sophisticated successor to the
|
|
<literal>Last-Modified</literal> header. When a server returns a
|
|
representation with an ETag header, the client can use this header in
|
|
subsequent GETs, in an <literal>If-None-Match</literal> header. If the
|
|
content has not changed, the server returns <literal>304: Not
|
|
Modified</literal>.</para>
|
|
|
|
<para>Support for ETags is provided by the servlet filter
|
|
<classname>ShallowEtagHeaderFilter</classname>. It is a plain Servlet
|
|
Filter, and thus can be used in combination with any web framework. <!--The preceding sentence was a fragment, not a complete sentence. Have I reworded ok?-->The
|
|
<classname>ShallowEtagHeaderFilter</classname> filter creates so-called
|
|
shallow ETags (as opposed to deep ETags, more about that later).<!--Provide xref to deep ETags.-->The
|
|
filter caches the content of the rendered JSP (or other content),
|
|
generates an MD5 hash over that, and returns that as an ETag header in the
|
|
response. The next time a client sends a request for the same resource, it
|
|
uses that hash as the <literal>If-None-Match</literal> value. The filter
|
|
detects this, renders the view again, and compares the two hashes. If they
|
|
are equal, a <literal>304</literal> is returned. This filter will not save
|
|
processing power, as the view is still rendered. The only thing it saves
|
|
is bandwidth, as the rendered response is not sent back over the
|
|
wire.</para>
|
|
|
|
<para>You configure the <classname>ShallowEtagHeaderFilter</classname> in
|
|
<filename>web.xml</filename>:</para>
|
|
|
|
<programlisting language="xml"><filter>
|
|
<filter-name>etagFilter</filter-name>
|
|
<filter-class>org.springframework.web.filter.ShallowEtagHeaderFilter</filter-class>
|
|
</filter>
|
|
|
|
<filter-mapping>
|
|
<filter-name>etagFilter</filter-name>
|
|
<servlet-name>petclinic</servlet-name>
|
|
</filter-mapping></programlisting>
|
|
</section>
|
|
|
|
<section id="mvc-resources">
|
|
<title>More Spring Web MVC Resources</title>
|
|
|
|
<para>See the following links and pointers for more resources about Spring
|
|
Web MVC:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>The Spring distribution ships with a Spring Web MVC tutorial
|
|
that guides the reader through building a complete Spring Web
|
|
MVC-based application using a step-by-step approach. This tutorial is
|
|
available in the <literal>docs</literal> directory of the Spring
|
|
distribution. An online version can also be found on the <ulink
|
|
url="http://springframework.org/">Spring Framework
|
|
website</ulink>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><quote>Expert Spring Web MVC and Web Flow</quote> by Seth Ladd
|
|
and others (published by Apress) is an excellent hard copy source of
|
|
Spring Web MVC goodness.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
</chapter>
|