3217 lines
145 KiB
XML
3217 lines
145 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</title>
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<para>Spring's Web MVC framework is designed around a
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<classname>DispatcherServlet</classname> that dispatches requests to
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handlers, with configurable handler mappings, view resolution, locale and
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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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your to create RESTful Web sites or application, though 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>One of the overarching design principles in Spring Web MVC (and in
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Spring in general) is the <quote><emphasis>Open for extension, closed
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for modification</emphasis></quote> principle.</para>
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<para>The reason that this principle is being mentioned here is because
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a number of methods in the core classes in Spring Web MVC are marked
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<literal>final</literal>. This means of course that you as a developer
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cannot override these methods to supply your own behavior... this is
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<emphasis>by design</emphasis> and has not been done arbitrarily to
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annoy.</para>
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<para>The book 'Expert Spring Web MVC and Web Flow' by Seth Ladd and
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others explains this principle and the reasons for adhering to it in
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some depth on page 117 (first edition) in the section entitled 'A Look
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At Design'.</para>
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<para>If you don't have access to the aforementioned book, then the
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following article may be of interest the next time you find yourself
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going <quote>Gah! Why can't I override this method?</quote> (if indeed
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you ever do).</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>Note that you cannot add advice to final methods using Spring MVC.
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This means it won't be possible to add advice to for example 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>Spring Web MVC allows you to use any object as a command or form
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backing object - there is no 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. All this means that
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you don't need to duplicate your business objects' properties as simple,
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untyped strings in your form objects just to be able to handle invalid
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submissions, or to convert the Strings properly. Instead, it is often
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preferable to bind directly to your 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. In the normal case, 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 (like a command or form, containing reference data).
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View name resolution is highly configurable, either via bean names, via a
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properties file, or via your own
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<interfacename>ViewResolver</interfacename> implementation. The fact that
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the model (the M in MVC) is based on the
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<interfacename>Map</interfacename> interface allows for the complete
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abstraction of the view technology. Any renderer can be integrated
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directly, whether JSP, Velocity, or any other rendering technology. The
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model <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-introduction-pluggability">
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<title>Pluggability of other MVC implementations</title>
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<para>There are several reasons why some projects will prefer to use
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other MVC implementations. Many teams expect to leverage their existing
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investment in skills and tools. In addition, there is a large body of
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knowledge and experience available for the Struts framework. Thus, if
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you can live with Struts' architectural flaws, it can still be a viable
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choice for the web layer; the same applies to WebWork and other web MVC
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frameworks.</para>
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<para>If you don't 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 via its
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<classname>ContextLoaderListener</classname>, and access it via its
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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. Note
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that there aren't any "plug-ins" involved, so no dedicated integration
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is necessary. From the web layer's point of view, you'll simply use
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Spring as a library, with the root application context instance as the
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entry point.</para>
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<para>All your registered beans and all of Spring's services can be at
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your fingertips even without Spring's Web MVC. Spring doesn't compete
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with Struts or WebWork in this scenario, it just addresses the many
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areas that the pure web MVC frameworks don't, from bean configuration to
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data access and transaction handling. So you are able to enrich your
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application with a Spring middle tier and/or data access tier, even if
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you just want to use, for example, the transaction abstraction with JDBC
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or Hibernate.</para>
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</section>
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<section id="mvc-features">
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<title>Features of Spring Web MVC</title>
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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 provides a wealth of unique web support
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features, including:</para>
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<itemizedlist>
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<listitem>
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<para>Clear separation of roles - controller, validator, command
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object, form object, model object,
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<classname>DispatcherServlet</classname>, handler mapping, view
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resolver, etc. Each role 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>Powerful and straightforward configuration of both framework
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and application classes as JavaBeans, including easy referencing
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across contexts, such as from web controllers to business objects
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and validators.</para>
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</listitem>
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<listitem>
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<para>Adaptability, non-intrusiveness, and flexibility. Define
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whatever controller method signature you need, possibly using one of
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the parameter annotations (such as @RequestParam, @RequestHeader,
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@PathVariable, and more) for a given scenario.</para>
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</listitem>
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<listitem>
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<para>Reusable business code - no need for duplication. You can use
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existing business objects as command or form objects instead of
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mirroring them in order to extend a particular framework base
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class.</para>
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</listitem>
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<listitem>
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<para>Customizable binding and validation - type mismatches as
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application-level validation errors that keep the offending value,
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localized date and number binding, etc instead of String-only form
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objects with manual parsing and conversion to business
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objects.</para>
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</listitem>
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<listitem>
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<para>Customizable handler mapping and view resolution - handler
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mapping and view resolution strategies range from simple URL-based
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configuration, to sophisticated, purpose-built resolution
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strategies. This is more flexible than some web MVC frameworks which
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mandate a particular technique.</para>
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</listitem>
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<listitem>
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<para>Flexible model transfer - model transfer via a name/value
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<interfacename>Map</interfacename> supports easy integration with
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any view technology.</para>
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</listitem>
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<listitem>
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<para>Customizable locale and theme resolution, support for JSPs
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with or without Spring tag library, support for JSTL, support for
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Velocity without the need for extra bridges, etc.</para>
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</listitem>
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<listitem>
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<para>A simple yet powerful JSP tag library known as the Spring tag
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library that provides support for features such as data binding and
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themes. The custom tags allow for maximum flexibility in terms of
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markup code. For information on the tag library descriptor, see the
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appendix entitled <xref linkend="spring.tld" /></para>
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</listitem>
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<listitem>
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<para>A JSP form tag library, introduced in Spring 2.0, that makes
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writing forms in JSP pages much easier. For information on the tag
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library descriptor, see the appendix entitled <xref
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linkend="spring-form.tld" /></para>
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</listitem>
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<listitem>
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<para>Beans whose lifecycle is scoped to the current HTTP request or
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HTTP <interfacename>Session</interfacename>. This is not a specific
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feature of Spring MVC itself, but rather of the
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<interfacename>WebApplicationContext</interfacename> container(s)
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that Spring MVC uses. These bean scopes are described in detail in
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the section entitled <xref
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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>
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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 facilitating the development
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of web applications. Spring's <classname>DispatcherServlet</classname>
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however, does more than just that. It is completely integrated with the
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Spring IoC container and as such allows you to use every other feature
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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> <emphasis>is</emphasis>
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an actual <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. Requests that you
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want the <classname>DispatcherServlet</classname> to handle will have to
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be mapped using a URL mapping in the same <literal>web.xml</literal> file.
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This is standard J2EE servlet configuration; an example of such a
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<classname>DispatcherServlet</classname> declaration and mapping can be
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found below.</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 example above, all requests ending with
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<literal>.form</literal> will be handled by the
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<literal>'example'</literal> <classname>DispatcherServlet</classname>.
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This is only the first step in setting up Spring Web MVC... the various
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beans used by the Spring Web MVC framework (over and above the
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<classname>DispatcherServlet</classname> itself) now need to be
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configured.</para>
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<para>As detailed in the section entitled <xref
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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, and new
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scope-specific beans can be defined 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><para>Context hierarchy in Spring Web MVC</para></caption>
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</mediaobject></para>
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<para>The framework will, on initialization of a
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<classname>DispatcherServlet</classname>, <emphasis>look for a file named
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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, you will need to have
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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 <emphasis>Spring Web
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MVC-specific</emphasis> components (beans). The exact location of this
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configuration file can be changed via a servlet initialization parameter
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(see below for details).</para>
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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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lookup the <interfacename>WebApplicationContext</interfacename> in case
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you need access to it.</para>
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<para>The Spring <classname>DispatcherServlet</classname> has a couple of
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special beans it uses in order to be able to process requests and render
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the appropriate views. These beans are included in the Spring framework
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and can be configured in the
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<interfacename>WebApplicationContext</interfacename>, just as any other
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bean would be configured. Each of those beans is described in more detail
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below. Right now, we'll just mention them, just to let you know they exist
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and to enable us to go on talking about the
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<classname>DispatcherServlet</classname>. For most of the beans, sensible
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defaults are provided so you don't (initially) have to worry about
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configuring them.</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>Controllers</entry>
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<entry><link linkend="mvc-controller">Controllers</link> are the
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components that form the <literal>'C'</literal> part of the
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MVC.</entry>
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</row>
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<row>
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<entry>Handler mappings</entry>
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<entry><link linkend="mvc-handlermapping">Handler mappings</link>
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handle the execution of a list of pre- and post-processors and
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controllers that will be executed if they match certain criteria
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(for instance a matching URL specified with the
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controller)</entry>
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</row>
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<row>
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<entry>View resolvers</entry>
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<entry><link linkend="mvc-viewresolver">View resolvers</link> are
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components capable of resolving view names to views</entry>
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</row>
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<row>
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<entry>Locale resolver</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>A <link linkend="mvc-multipart">multipart file
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resolver</link> offers the functionality to process file uploads
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|
from HTML forms</entry>
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</row>
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<row>
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<entry>Handler exception resolver(s)</entry>
|
|
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<entry><link linkend="mvc-exceptionhandlers">Handler exception
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|
resolvers</link> offer 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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|
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<para>When a <classname>DispatcherServlet</classname> is set up for use
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and a request comes in for that specific
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<classname>DispatcherServlet</classname>, said
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<classname>DispatcherServlet</classname> starts processing the request.
|
|
The list below describes the complete process a request goes through when
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handled by a <classname>DispatcherServlet</classname>:</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 in order for the
|
|
controller and other elements in the process to use. It 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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|
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<listitem>
|
|
<para>The locale resolver is bound to the request to let elements in
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the process resolve the locale to use when processing the request
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|
(rendering the view, preparing data, etc.) If you don't use the
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resolver, it won't affect anything, so if you don't need locale
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resolving, you don't have to use it.</para>
|
|
</listitem>
|
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|
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<listitem>
|
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<para>The theme resolver is bound to the request to let elements such
|
|
as views determine which theme to use. The theme resolver does not
|
|
affect anything if you don't use it, so if you don't need themes you
|
|
can just ignore it.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If a multipart resolver is specified, 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 the section entitled
|
|
<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) will be executed in order to prepare
|
|
a model (for rendering).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If a model is returned, the view is rendered. If no model is
|
|
returned (which could be due to a pre- or postprocessor intercepting
|
|
the request, for example, for security reasons), no view is rendered,
|
|
since the request could already have been fulfilled.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>Exceptions that are thrown during processing of the request get
|
|
picked up by any of the handler exception resolvers that are declared in
|
|
the <interfacename>WebApplicationContext</interfacename>. Using these
|
|
exception resolvers allows you to define custom behaviors in case such
|
|
exceptions get thrown.</para>
|
|
|
|
<para>The Spring <classname>DispatcherServlet</classname> also has support
|
|
for returning 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> will first lookup an appropriate
|
|
handler mapping and test if the handler that is found <emphasis>implements
|
|
the interface <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. The possibilities are listed
|
|
below.</para>
|
|
|
|
<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 will
|
|
be used to instantiate the context used by this servlet. If this
|
|
parameter isn't specified, the
|
|
<classname>XmlWebApplicationContext</classname> will be
|
|
used.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><literal>contextConfigLocation</literal></entry>
|
|
|
|
<entry>String which is passed to the context instance (specified
|
|
by <literal>contextClass</literal>) to indicate where context(s)
|
|
can be found. The string is potentially split up into multiple
|
|
strings (using a comma as a delimiter) to support multiple
|
|
contexts (in case of multiple context locations, of beans that are
|
|
defined twice, the latest takes precedence).</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><literal>namespace</literal></entry>
|
|
|
|
<entry>the namespace of the
|
|
<interfacename>WebApplicationContext</interfacename>. Defaults to
|
|
<literal>[servlet-name]-servlet</literal>.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</section>
|
|
|
|
<section id="mvc-controller">
|
|
<title>Controllers</title>
|
|
|
|
<para>The notion of a controller is part of the MVC design pattern (more
|
|
specifically, it is the <emphasis>'C'</emphasis> in MVC). Controllers
|
|
provide access to the application behavior which is typically defined by a
|
|
service interface. Controllers interpret user input and transform such
|
|
input into a sensible model which will be represented to the user by the
|
|
view. Spring has implemented the notion of a controller in a very abstract
|
|
way enabling a wide variety of different kinds of controllers to be
|
|
created.</para>
|
|
|
|
<para>Spring 2.5 introduced an annotation-based programming model for MVC
|
|
controllers, using annotations such as
|
|
<interfacename>@RequestMapping</interfacename>,
|
|
<interfacename>@RequestParam</interfacename>,
|
|
<interfacename>@ModelAttribute</interfacename>, etc. 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 API's, although they can easily
|
|
get access to Servlet or Portlet facilities if desired.</para>
|
|
|
|
<tip>
|
|
<para>The Spring distribution ships with the
|
|
<emphasis>PetClinic</emphasis> sample, which is a web application that
|
|
takes advantage of the annotation support described in this section, in
|
|
the context of simple form processing. You can find the
|
|
<emphasis>PetClinic</emphasis> application in the
|
|
<literal>'samples/petclinic'</literal> directory.</para>
|
|
|
|
<para>For a further sample application that builds on annotation-based
|
|
Web MVC, check out <emphasis>imagedb</emphasis>. The focus in that
|
|
sample is on stateless multi-action controllers, including the
|
|
processing of multipart file uploads. You can find the
|
|
<emphasis>imagedb</emphasis> application in the
|
|
<literal>'samples/imagedb'</literal> directory.</para>
|
|
</tip>
|
|
|
|
<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 for
|
|
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, as will be 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 document 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>. There is no need to extend any
|
|
controller base class or reference the Servlet API. You are of course
|
|
still able to reference Servlet-specific features if you need to.</para>
|
|
|
|
<para>The basic purpose of the
|
|
<interfacename>@Controller</interfacename> annotation is to act as a
|
|
stereotype for the annotated class, indicating its role. The dispatcher
|
|
will scan such annotated classes for mapped methods, detecting
|
|
<interfacename>@RequestMapping</interfacename> annotations (see the next
|
|
section).</para>
|
|
|
|
<para>Annotated controller beans may be defined 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>
|
|
|
|
<para>To enable autodetection of such annotated controllers, you have to
|
|
add component scanning to your configuration. This is easily achieved by
|
|
using 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>The <interfacename>@RequestMapping</interfacename> annotation is
|
|
used to map URLs like <filename>/appointments</filename> onto an entire
|
|
class or a particular handler method. It can be used to annotate both a
|
|
class or 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, above, we see that 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 will be relative to the
|
|
<filename>/appointments</filename> path. Next, we see that 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> will result in this method being
|
|
invoked. 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.
|
|
We will discuss these in <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 is an example of a multi-action controller
|
|
from the PetClinic sample application 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 easily access (parts of) a request URL in your handling
|
|
methods, Spring MVC allows for the use of <emphasis>URI
|
|
templates</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 these variables are substituted for values, the
|
|
template becomes a URI The <ulink
|
|
url="http://bitworking.org/projects/URI-Templates/">proposed
|
|
RFC</ulink> for URI Templates defines how an URI is parameterized.
|
|
For example, the URI Template</para>
|
|
|
|
<programlisting>http://www.example.com/users/{userid}</programlisting>
|
|
|
|
<para>contains the variable 'userid'. If we assign the variable the
|
|
value "fred", then 'expanding' the URI Template gives.</para>
|
|
|
|
<programlisting>http://www.example.com/users/fred</programlisting>
|
|
|
|
<para>When processing a request the URI can be compared to an
|
|
expected URI Template in order to extract a collection of
|
|
variables.</para>
|
|
</sidebar>
|
|
|
|
<para>The <interfacename>@PathVariable</interfacename> method
|
|
parameter annotation is used 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 ownerId. When the controller handles this
|
|
request, the value of ownerId is set 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>
|
|
|
|
<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 to bind to in the @PathVariable
|
|
annotation. 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>The name of the method parameter does not matter in this case,
|
|
so you may also use a controller method with the signature shown
|
|
below</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>Multiple @PathVariable annotations can be used to bind to
|
|
multiple URI Template variables as shown below:</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 customizing 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 (e.g.
|
|
<filename>/myPath/*.do</filename>). A combination of URI templates and
|
|
Ant-style globs is also supported (e.g.
|
|
<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>).
|
|
Note that this only applies in case of ambiguous annotation mappings
|
|
that 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 will be dispatched to it. If you have multiple such default
|
|
methods, then the method name will be taken into account for choosing
|
|
between them.</para>
|
|
|
|
<para>Path mappings can be narrowed 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). 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>
|
|
will only be invoked when the Content-Type is in the
|
|
<literal>text/*</literal> range, for instance
|
|
<literal>text/xml</literal>.</para>
|
|
</section>
|
|
|
|
<section id="mvc-ann-requestmapping-arguments">
|
|
<title>Supported handler method arguments and return types</title>
|
|
|
|
<para>Handler methods which are annotated with
|
|
<classname>@RequestMapping</classname> are allowed to 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):
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Request and/or response objects (Servlet API). You may
|
|
choose any specific request/response type, e.g.
|
|
<interfacename>ServletRequest</interfacename> /
|
|
<interfacename>HttpServletRequest</interfacename>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Session object (Servlet API): of type
|
|
<interfacename>HttpSession</interfacename>. An argument of this
|
|
type will enforce the presence of a corresponding session. As a
|
|
consequence, such an argument will never be
|
|
<literal>null</literal>.</para>
|
|
|
|
<note>
|
|
<para>Note that 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, i.e. 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 will be 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 will be 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 will be 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 will be 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 will be
|
|
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 will be exposed to the web
|
|
view.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Command/form objects to bind parameters to: as bean
|
|
properties or fields, 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 (e.g. "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/form object (the
|
|
immediate preceding argument).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><classname>org.springframework.web.bind.support.SessionStatus</classname>
|
|
status handle for marking form processing as complete
|
|
(triggering 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).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>A <classname>String</classname> value which is interpreted
|
|
as 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
|
|
will be 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 will be 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's class name otherwise). The model will be 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>The <classname>@RequestParam</classname> annotation is used 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 is used to indicate 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>The conversion of the request body to the method argument is
|
|
done 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 the
|
|
<classname>AnnotationMethodHandlerAdapter</classname> has been
|
|
extended to support the <classname>@RequestBody</classname> and has
|
|
several <interfacename>HttpMessageConverters</interfacename>
|
|
registered by default, these are</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>More information on these converters can be found in the section
|
|
<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>Similar to <interfacename>@RequestBody</interfacename>, there is
|
|
the <interfacename>@ResponseBody</interfacename> annotation. This
|
|
annotation can be put on 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 above will result in the text <literal>Hello
|
|
World</literal> being written to the HTTP response stream.</para>
|
|
|
|
<para>Just like <interfacename>@RequestBody</interfacename>, the
|
|
conversion of the returned object to response body is done using a
|
|
<interfacename>HttpMessageConverter</interfacename>. More information
|
|
on these converters can be found in the previous section, or in the
|
|
section <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 placed on a method parameter,
|
|
<classname>@ModelAttribute</classname> is used to map 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><classname>@ModelAttribute</classname> is also used at the
|
|
method level to provide <emphasis>reference data</emphasis> for the
|
|
model (see the <literal>populatePetTypes()</literal> method below).
|
|
For this usage the method signature can contain the same types as
|
|
documented above for the <classname>@RequestMapping</classname>
|
|
annotation.</para>
|
|
|
|
<note>
|
|
<para><emphasis>Note:</emphasis>
|
|
<classname>@ModelAttribute</classname> annotated methods will be
|
|
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,
|
|
etc. via Spring's <classname>WebDataBinder</classname>, you can either
|
|
use <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 which
|
|
initialize the <classname>WebDataBinder</classname> which will be
|
|
used for populating 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> for configuring 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 MVC, 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, 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>: the list of interceptors to
|
|
use. <interfacename>HandlerInterceptor</interfacename>s are discussed
|
|
in <xref linkend="mvc-handlermapping-interceptor" />.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><literal>defaultHandler</literal>: the 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 will sort all handler mappings available in the
|
|
context and apply the first matching handler.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><literal>alwaysUseFullPath</literal>: if this property is set to
|
|
<literal>true</literal>, Spring will use the full path within the
|
|
current servlet context to find an appropriate handler. If this
|
|
property is set to <literal>false</literal> (the default), the path
|
|
within the current servlet mapping will be 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> would be used, whereas if
|
|
the property is set to false, <literal>/viewPage.html</literal> would
|
|
be used.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><literal>urlDecode</literal>: the default value for this
|
|
property is <literal>true</literal>, as of Spring 2.5. If you prefer
|
|
to compare encoded paths, switch this flag to
|
|
<literal>false</literal>. However, note that 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 for lazy
|
|
initialization of <emphasis>singleton</emphasis> handlers (prototype
|
|
handlers are always lazily initialized). Default value is
|
|
<literal>false</literal>.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>(<emphasis>Note: the last three properties are only available to
|
|
subclasses of
|
|
<classname>org.springframework.web.servlet.handler.AbstractUrlHandlerMapping</classname></emphasis>).</para>
|
|
|
|
<para>The following example shows how to override the default mapping, and add an interceptor:</para>
|
|
|
|
<programlisting language="xml"><![CDATA[<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</title>
|
|
|
|
<para>Spring's handler mapping mechanism has the notion of handler
|
|
interceptors, that can be extremely 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 that will be called
|
|
<emphasis>before</emphasis> the actual handler will be executed, one
|
|
that will be called <emphasis>after</emphasis> the handler is executed,
|
|
and one that is called <emphasis>after the complete request has
|
|
finished</emphasis>. These three methods should provide enough
|
|
flexibility to do all kinds of pre- and post-processing.</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, will be intercepted by the
|
|
<classname>TimeBasedAccessInterceptor</classname>, and if the current
|
|
time is outside office hours, the user will be redirected to a static
|
|
html file, saying, for example, he can only access the website during
|
|
office hours.</para>
|
|
|
|
<para>As you can see, Spring has an adapter class (the cunningly named
|
|
<classname>HandlerInterceptorAdapter</classname>) to make it easier to
|
|
extend the <interfacename>HandlerInterceptor</interfacename>
|
|
interface.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-viewresolver">
|
|
<title>Views and resolving them</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. The section entitled <xref linkend="view" /> has details of
|
|
how to integrate and use a number of disparate view technologies.</para>
|
|
|
|
<para>The two interfaces which 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 - the <interfacename>ViewResolver</interfacename>
|
|
interface</title>
|
|
|
|
<para>As discussed in the section entitled <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. We'll list most
|
|
of them and then provide a couple of examples.</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>An abstract view resolver which takes care of caching
|
|
views. Often views need preparation before they can be used,
|
|
extending this view resolver provides caching of views.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>XmlViewResolver</classname></entry>
|
|
|
|
<entry>An 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>An implementation of
|
|
<interfacename>ViewResolver</interfacename> that uses bean
|
|
definitions in a <classname>ResourceBundle</classname>,
|
|
specified by the bundle basename. The bundle is typically
|
|
defined in a properties file, located in the classpath. The
|
|
default file name is
|
|
<literal>views.properties</literal>.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>UrlBasedViewResolver</classname></entry>
|
|
|
|
<entry>A 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>A convenience subclass of
|
|
<classname>UrlBasedViewResolver</classname> that supports
|
|
<classname>InternalResourceView</classname> (i.e. Servlets and
|
|
JSPs), and subclasses such as <classname>JstlView</classname>
|
|
and <classname>TilesView</classname>. The view class for all
|
|
views generated by this resolver can be specified via
|
|
<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>A convenience subclass of
|
|
<classname>UrlBasedViewResolver</classname> that supports
|
|
<classname>VelocityView</classname> (i.e. Velocity templates) or
|
|
<classname>FreeMarkerView</classname> respectively and custom
|
|
subclasses of them.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>ContentNegotiatingViewResolver</classname></entry>
|
|
|
|
<entry>An implementation of the <interfacename>ViewResolver</interfacename>
|
|
interface that 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, when using JSP for 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 will hand the request over to the
|
|
<classname>RequestDispatcher</classname> that will send the request to
|
|
<literal>/WEB-INF/jsp/test.jsp</literal>.</para>
|
|
|
|
<para>When mixing 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. This way you can specify a default
|
|
view class, for example.</para>
|
|
|
|
<para><emphasis>A note on caching</emphasis> - subclasses of
|
|
<classname>AbstractCachingViewResolver</classname> cache view instances
|
|
they have resolved. This greatly improves performance when using 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 have the requirement to be able to refresh a certain
|
|
view at runtime (for example when a Velocity template has been
|
|
modified), you can use the <literal>removeFromCache(String viewName,
|
|
Locale loc)</literal> method.</para>
|
|
</section>
|
|
|
|
<section id="mvc-viewresolver-chaining">
|
|
<title>Chaining ViewResolvers</title>
|
|
|
|
<para>Spring supports more than just one view resolver. This allows you
|
|
to chain resolvers and, for example, override specific views in certain
|
|
circumstances. Chaining view resolvers is pretty straightforward - just
|
|
add more than one resolver to your application context and, if
|
|
necessary, set the <literal>order</literal> property to specify an
|
|
order. Remember, the higher the order property, the later the view
|
|
resolver will be 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 (which are not supported by the
|
|
<classname>InternalResourceViewResolver</classname>):</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 will
|
|
inspect the context to see if other view resolvers are configured. If
|
|
there are additional view resolvers, it will continue to inspect them.
|
|
If not, it will throw an <classname>Exception</classname>.</para>
|
|
|
|
<para>You have to keep something else in mind - the contract of a view
|
|
resolver mentions that a view resolver <emphasis>can</emphasis> return
|
|
null to indicate the view could not be found. Not all view resolvers do
|
|
this however! This is 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 - this can only be done once.
|
|
The same holds for the <classname>VelocityViewResolver</classname> and
|
|
some others. Check the Javadoc for the view resolver to see if you're
|
|
dealing with a view resolver that does not report non-existing views. As
|
|
a result of this, putting an
|
|
<classname>InternalResourceViewResolver</classname> in the chain in a
|
|
place other than the last, will result in the chain not being fully
|
|
inspected, since the <classname>InternalResourceViewResolver</classname>
|
|
will <emphasis>always</emphasis> return a view!</para>
|
|
</section>
|
|
|
|
<section id="mvc-redirecting">
|
|
<title>Redirecting to views</title>
|
|
|
|
<para>As has been mentioned, a controller normally returns a logical
|
|
view name, which a view resolver resolves to a particular view
|
|
technology. For view technologies such as JSPs that are actually
|
|
processed via the Servlet/JSP engine, this is normally handled via
|
|
<classname>InternalResourceViewResolver</classname> /
|
|
<classname>InternalResourceView</classname> which will ultimately end up
|
|
issuing an internal forward or include, via the Servlet API's
|
|
<literal>RequestDispatcher.forward(..)</literal> or
|
|
<literal>RequestDispatcher.include()</literal>. For other view
|
|
technologies, such as Velocity, XSLT, etc., 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
|
|
would just force 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> will not use the normal view
|
|
resolution mechanism, but rather as it has been given the (redirect)
|
|
view already, will just ask it to do its work.</para>
|
|
|
|
<para>The <classname>RedirectView</classname> simply ends up issuing
|
|
an <literal>HttpServletResponse.sendRedirect()</literal> call, which
|
|
will come back to the client browser as an HTTP redirect. All model
|
|
attributes are simply 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 using <classname>RedirectView</classname> and the view is
|
|
created by the controller itself, it is preferable for 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.</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... it should generally think only in terms of view names that
|
|
have been injected into it.</para>
|
|
|
|
<para>The special <literal>redirect:</literal> prefix allows this to
|
|
be achieved. If a view name is returned which has the prefix
|
|
redirect:, then <classname>UrlBasedViewResolver</classname> (and all
|
|
subclasses) will 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
|
|
deal just 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</title>
|
|
|
|
<para>It is also possible to use a special <literal>forward:</literal>
|
|
prefix for view names that will ultimately be 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, there is never any use in using this prefix when using
|
|
<classname>InternalResourceViewResolver</classname> /
|
|
<classname>InternalResourceView</classname> anyway (for JSPs for
|
|
example), but it's of potential use when you are primarily using
|
|
another view technology, but still want to force a forward to happen
|
|
to a resource to be handled by the Servlet/JSP engine. (Note that you
|
|
may also chain multiple view resolvers, instead.)</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 have to be aware that anything special is
|
|
happening in terms of handling the response.</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.
|
|
There are two strategies for a client to inform the server of
|
|
the representation it is interested in receiving.</para>
|
|
|
|
<para>The first strategy is to use a distinct URI for each resource.
|
|
This is typically done 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 while
|
|
<literal>http://www.example.com/users/fred.xml</literal> requests an XML
|
|
representation.</para>
|
|
|
|
<para>The second strategy is for the client to use the same URI 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, a 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>
|
|
|
|
<note>
|
|
<para>One issue with the Accept header is that is impossible to change
|
|
it in a web browser, in HTML. For instance, in Firefox, it's fixed
|
|
to</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 set using the bean property
|
|
<literal>ViewResolvers</literal>.</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 (a.k.a.
|
|
<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> is used to return the representation to
|
|
the client. The <literal>Accept</literal> header may include wild cards,
|
|
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,
|
|
<classname>ContentNegotiatingViewResolver</classname>'s bean property
|
|
<literal>MediaTypes</literal> is used 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"><![CDATA[<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 - 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'.</para>
|
|
|
|
<para>In this configuration, if a request is made with a .html extension
|
|
the view resolver will look 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 will look 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 'content'. Alternatively, client requests could 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.</para>
|
|
|
|
<note>
|
|
<para>If <classname>ContentNegotiatingViewResolver</classname>'s list
|
|
of ViewResolvers is not configured explicitly, then it will
|
|
automatically use 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>Using this parameter, you can limit 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.</para>
|
|
</section>
|
|
|
|
<section id="mvc-localeresolver-interceptor">
|
|
<title><classname>LocaleChangeInterceptor</classname></title>
|
|
|
|
<para>You can build in changing of locales using the
|
|
<classname>LocaleChangeInterceptor</classname>. This interceptor needs
|
|
to be added 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).</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>
|
|
|
|
<para>All calls to all <literal>*.view</literal> resources containing a
|
|
parameter named <literal>siteLanguage</literal> will now change the
|
|
locale. So a request for the following URL,
|
|
<literal>http://www.sf.net/home.view?siteLanguage=nl</literal> will
|
|
change the site language to Dutch.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-themeresolver">
|
|
<title>Using themes</title>
|
|
|
|
<section id="mvc-themeresolver-introduction">
|
|
<title>Introduction</title>
|
|
|
|
<para>The <emphasis>theme</emphasis> support provided by the Spring web
|
|
MVC framework enables you to further enhance the user experience by
|
|
allowing the look and feel of your application to be
|
|
<emphasis>themed</emphasis>. A theme is basically a collection of static
|
|
resources affecting the visual style of the application, typically style
|
|
sheets and images.</para>
|
|
</section>
|
|
|
|
<section id="mvc-themeresolver-defining">
|
|
<title>Defining themes</title>
|
|
|
|
<para>When you want to use themes in your web application you'll have to
|
|
set up a
|
|
<interfacename>org.springframework.ui.context.ThemeSource</interfacename>.
|
|
The <interfacename>WebApplicationContext</interfacename> interface
|
|
extends <interfacename>ThemeSource</interfacename> but delegates its
|
|
responsibilities to a dedicated implementation. By default the delegate
|
|
will be a
|
|
<classname>org.springframework.ui.context.support.ResourceBundleThemeSource</classname>
|
|
that loads properties files from the root of the classpath. If you want
|
|
to use a custom <interfacename>ThemeSource</interfacename>
|
|
implementation or if you need to configure the basename prefix of the
|
|
<classname>ResourceBundleThemeSource</classname>, you can register a
|
|
bean in the application context with the reserved name "themeSource".
|
|
The web application context will automatically detect that bean and
|
|
start using it.</para>
|
|
|
|
<para>When using the <classname>ResourceBundleThemeSource</classname>, a
|
|
theme is defined in a simple properties file. The properties file lists
|
|
the resources that make up the theme. Here is an example:</para>
|
|
|
|
<programlisting>styleSheet=/themes/cool/style.css
|
|
background=/themes/cool/img/coolBg.jpg</programlisting>
|
|
|
|
<para>The keys of the properties are the names used to refer to the
|
|
themed elements from view code. For a JSP this would typically be done
|
|
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 above 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 basename prefix. As a result the properties files will be
|
|
loaded from the root of the classpath, so we'll have to put our
|
|
<literal>cool.properties</literal> theme definition in a directory at
|
|
the root of the classpath, e.g. in <literal>/WEB-INF/classes</literal>.
|
|
Note that the <classname>ResourceBundleThemeSource</classname> uses the
|
|
standard Java resource bundle loading mechanism, allowing for full
|
|
internationalization of themes. For instance, we could have a
|
|
<literal>/WEB-INF/classes/cool_nl.properties</literal> that references a
|
|
special background image, e.g. with Dutch text on it.</para>
|
|
</section>
|
|
|
|
<section id="mvc-themeresolver-resolving">
|
|
<title>Theme resolvers</title>
|
|
|
|
<para>Now that we have our themes defined, the only thing left to do is
|
|
decide which theme to use. The <classname>DispatcherServlet</classname>
|
|
will look for a bean named "themeResolver" 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 can detect the theme
|
|
that should be used 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 "defaultThemeName"
|
|
property.</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><classname>SessionThemeResolver</classname></entry>
|
|
|
|
<entry>The theme is maintained in the users 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 changing the
|
|
theme on every request by including a simple request parameter.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-multipart">
|
|
<title>Spring's multipart (fileupload) support</title>
|
|
|
|
<section id="mvc-multipart-introduction">
|
|
<title>Introduction</title>
|
|
|
|
<para>Spring has built-in multipart support to handle fileuploads in web
|
|
applications. The design for the multipart support is done with
|
|
pluggable <interfacename>MultipartResolver</interfacename> objects,
|
|
defined in the <literal>org.springframework.web.multipart</literal>
|
|
package. 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>). How
|
|
uploading files is supported will be described in the rest of this
|
|
chapter.</para>
|
|
|
|
<para>By default, no multipart handling will be done by Spring, as some
|
|
developers will want to handle multiparts themselves. You will have to
|
|
enable it yourself by adding a multipart resolver to the web
|
|
application's context. After you have done that, each request will be
|
|
inspected to see if it contains a multipart. If no multipart is found,
|
|
the request will continue as expected. However, if a multipart is found
|
|
in the request, the <classname>MultipartResolver</classname> that has
|
|
been declared in your context will be used. After that, the multipart
|
|
attribute in your request will be 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 is an example using 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>Now that you have seen how to set Spring up to handle multipart
|
|
requests, let's talk about how to actually use it. 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. What the resolver then does is wrap the current
|
|
<classname>HttpServletRequest</classname> into a
|
|
<classname>MultipartHttpServletRequest</classname> that has support for
|
|
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> has finished
|
|
doing its job, the request will be processed like any other. To use it,
|
|
you create a form with an upload field (see immediately below), then let
|
|
Spring bind the file onto your form (backing object). To actually let
|
|
the user upload a file, we have to create a (HTML) form:</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>. Furthermore we've
|
|
added the encoding attribute
|
|
(<literal>enctype="multipart/form-data"</literal>) which is necessary to
|
|
let the browser know how to encode the multipart fields (do not forget
|
|
this!).</para>
|
|
|
|
<para>Just as with any other property that's not automagically
|
|
convertible to a string or primitive type, to be able to put binary data
|
|
in your objects you have to register a custom editor with the
|
|
<classname>ServletRequestDatabinder</classname>. There are a couple of
|
|
editors available for handling files and setting the results on an
|
|
object. There's a <classname>StringMultipartEditor</classname> capable
|
|
of converting files to Strings (using a user-defined character set) and
|
|
there is a <classname>ByteArrayMultipartEditor</classname> which
|
|
converts files to byte arrays. They function just as the
|
|
<classname>CustomDateEditor</classname> does.</para>
|
|
|
|
<para>So, to be able to upload files using a (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.</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 actually
|
|
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 whatever you want (save it in a database, mail it to
|
|
somebody, etc).</para>
|
|
|
|
<para>An equivalent example in which a file is bound straight to a
|
|
String-typed property on a (form backing) object might look like:</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>Of course, this last example only makes (logical) sense in the
|
|
context of uploading a plain text file (it wouldn't work so well in the
|
|
case of uploading an image file).</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>
|
|
|
|
<para>Spring provides <literal>HandlerExceptionResolvers</literal> to ease
|
|
the pain of unexpected exceptions occurring while your request is being
|
|
handled by a controller which 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 what handler was
|
|
executing when the exception was thrown. Furthermore, a programmatic way
|
|
of handling exception gives you many more options for how to respond
|
|
appropriately before the request is forwarded to another URL (the same end
|
|
result as when using 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's also possible to
|
|
implement more finely grained mappings of exceptions from different
|
|
handlers.</para>
|
|
|
|
<section id="mvc-ann-exceptionhandler">
|
|
<title><interfacename>@ExceptionResolver</interfacename></title>
|
|
|
|
<para>As an alternative to implementing the <interfacename>HandlerExceptionResolver</interfacename>, you
|
|
can use the <interfacename>@ExceptionHandler</interfacename>. The <classname>@ExceptionHandler</classname> method annotation is
|
|
used within a controller to specify which method will be 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. Please refer to the API
|
|
documentation for more details.</para>
|
|
</section>
|
|
|
|
</section>
|
|
|
|
<section id="mvc-coc">
|
|
<title>Convention over configuration</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>This convention over configuration support address the three core
|
|
areas of MVC - namely, the 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>An example; consider the following (simplistic)
|
|
<interfacename>Controller</interfacename> implementation. Take especial
|
|
notice of the <emphasis>name</emphasis> of the class.</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.</para>
|
|
|
|
<para>Let's look at some more examples so that the central idea becomes
|
|
immediately familiar.</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>
|
|
|
|
<listitem>
|
|
<para><classname>DisplayShoppingCartController</classname> maps to
|
|
the <literal>'/displayshoppingcart*'</literal> request URL</para>
|
|
|
|
<para><emphasis>(Notice the casing - all lowercase - in the case of
|
|
camel-cased <interfacename>Controller</interfacename> class
|
|
names.)</emphasis></para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>In the case of <classname>MultiActionController</classname>
|
|
handler classes, the mappings generated are (ever so slightly) more
|
|
complex, but hopefully no less understandable. Some examples (all of the
|
|
<interfacename>Controller</interfacename> names in this next bit 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 pretty standard convention of naming your
|
|
<interfacename>Controller</interfacename> implementations as
|
|
<literal>xxx<emphasis role="bold">Controller</emphasis></literal>, then
|
|
the <classname>ControllerClassNameHandlerMapping</classname> will save
|
|
you the tedium of having to firstly define and then having to maintain 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 like 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 being 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. Find below some examples of the 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'll
|
|
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 potentially 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 to say, you cannot add a
|
|
<interfacename>List</interfacename> of <classname>Person</classname>
|
|
objects to a <classname>ModelAndView</classname> and have the
|
|
generated name be 'people'.</para>
|
|
|
|
<para>This decision was taken 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
|
|
(i.e. 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 is responsible for determining a logical
|
|
<interfacename>View</interfacename> name when no such logical view name
|
|
is explicitly supplied. It has just one implementation, the rather
|
|
cunningly named
|
|
<classname>DefaultRequestToViewNameTranslator</classname> class.</para>
|
|
|
|
<para>The <classname>DefaultRequestToViewNameTranslator</classname> maps
|
|
request URLs to logical view names in a fashion that is probably best
|
|
explained by recourse to an 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. It is the
|
|
<classname>DefaultRequestToViewNameTranslator</classname> that will be
|
|
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 being used in
|
|
conjunction with the
|
|
<classname>ControllerClassNameHandlerMapping</classname>, a request URL
|
|
of <literal>'http://localhost/registration.html'</literal> will result
|
|
in a logical view name of <literal>'registration'</literal> being
|
|
generated by the
|
|
<classname>DefaultRequestToViewNameTranslator</classname>. This logical
|
|
view name will then be resolved into the
|
|
<literal>'/WEB-INF/jsp/registration.jsp'</literal> view by the
|
|
<classname>InternalResourceViewResolver</classname> bean.</para>
|
|
|
|
<tip>
|
|
<para>You don't even need to define a
|
|
<classname>DefaultRequestToViewNameTranslator</classname> bean
|
|
explicitly. If you are okay with the default settings of the
|
|
<classname>DefaultRequestToViewNameTranslator</classname>, then you
|
|
can rely on the fact that the Spring Web MVC
|
|
<classname>DispatcherServlet</classname> will actually 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. Please do consult the quite comprehensive Javadoc for the
|
|
<classname>DefaultRequestToViewNameTranslator</classname> class for
|
|
details of the various properties that can be configured.</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="mvc-resources">
|
|
<title>Further Resources</title>
|
|
|
|
<para>Find below links and pointers to further 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>The book entitled <quote>Expert Spring Web MVC and Web
|
|
Flow</quote> by Seth Ladd and others (published by Apress) is an
|
|
excellent hardcopy source of Spring Web MVC goodness.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
</chapter>
|