Rossen Stoyanchev
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11ac87099a
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10dcaa9bf6
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@ -29,7 +29,7 @@ This reference document provides the following sections:
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* <<data-access.adoc#spring-data-tier,Data access and transaction management>>
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* <<web.adoc#spring-web,Web frameworks>>
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* <<web.adoc#spring-web,The Web>>
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* <<integration.adoc#spring-integration,Integration with other technologies>>
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@ -11,7 +11,7 @@ or on a reactive stack (Reactive Streams API + non-blocking runtime).
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The first few chapters cover the Servlet-based <<mvc,Spring MVC>> web framework
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including <<view,Views>>, <<cors,CORS>>, and <<websocket,WebSocket>> support.
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Subsequent chapters cover the <<webflux,Spring WebFlux>> reactive web framework
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including its <<webflux-fn,WebFlux.fn>> functional programming model.
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including its <<webflux-fn,functional programming model>>.
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include::web/web-mvc.adoc[leveloffset=+1]
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@ -6,24 +6,6 @@
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[[intro]]
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== Introduction
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.Spring Web Flow
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****
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Spring Web Flow (SWF) aims to be the best solution for the management of web application
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page flow.
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SWF integrates with existing frameworks like Spring MVC and JSF, in both Servlet and
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Portlet environments. If you have a business process (or processes) that would benefit
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from a conversational model as opposed to a purely request model, then SWF may be the
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solution.
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SWF allows you to capture logical page flows as self-contained modules that are reusable
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in different situations, and as such is ideal for building web application modules that
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guide the user through controlled navigations that drive business processes.
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For more information about SWF, consult the
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http://projects.spring.io/spring-webflow/[Spring Web Flow website].
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****
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This chapter details Spring's integration with third party web frameworks, such as
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http://www.oracle.com/technetwork/java/javaee/javaserverfaces-139869.html[JSF].
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@ -3,279 +3,89 @@
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:doc-spring-security: {doc-root}/spring-security/site/docs/current/reference
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[[mvc-introduction]]
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== Introduction to Spring Web MVC framework
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The Spring Web model-view-controller (MVC) framework is designed around a
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`DispatcherServlet` that dispatches requests to handlers, with configurable handler
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mappings, view resolution, locale, time zone and theme resolution as well as support for
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uploading files. The default handler is based on the `@Controller` and `@RequestMapping`
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annotations, offering a wide range of flexible handling methods. With the introduction
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of Spring 3.0, the `@Controller` mechanism also allows you to create RESTful Web sites
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and applications, through the `@PathVariable` annotation and other features.
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****
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"Open for extension..."
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A key design principle in Spring Web MVC and in Spring in general is the "__Open for
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extension, closed for modification__" principle.
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Some methods in the core classes of Spring Web MVC are marked `final`. As a developer
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you cannot override these methods to supply your own behavior. This has not been done
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arbitrarily, but specifically with this principle in mind.
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For an explanation of this principle, refer to __Expert Spring Web MVC and Web Flow__ by
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Seth Ladd and others; specifically see the section "A Look At Design," on page 117 of
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the first edition. Alternatively, see
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* https://www.cs.duke.edu/courses/fall07/cps108/papers/ocp.pdf[Bob Martin, The Open-Closed
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Principle (PDF)]
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You cannot add advice to final methods when you use Spring MVC. For example, you cannot
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add advice to the `AbstractController.setSynchronizeOnSession()` method. Refer to
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<<core.adoc#aop-understanding-aop-proxies, Understanding AOP proxies>>
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for more information on AOP proxies and why you cannot add advice to final methods.
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****
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In Spring Web MVC you can use any object as a command or form-backing object; you do not
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need to implement a framework-specific interface or base class. Spring's data binding is
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highly flexible: for example, it treats type mismatches as validation errors that can be
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evaluated by the application, not as system errors. Thus you do not need to duplicate your
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business objects' properties as simple, untyped strings in your form objects simply to
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handle invalid submissions, or to convert the Strings properly. Instead, it is often
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preferable to bind directly to your business objects.
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Spring's view resolution is extremely flexible. A `Controller` is typically responsible
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for preparing a model `Map` with data and selecting a view name but it can also write
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directly to the response stream and complete the request. View name resolution is highly
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configurable through file extension or Accept header content type negotiation, through
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bean names, a properties file, or even a custom `ViewResolver` implementation. The model
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(the M in MVC) is a `Map` interface, which allows for the complete abstraction of the
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view technology. You can integrate directly with template based rendering technologies
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such as JSP and FreeMarker, or directly generate XML, JSON, Atom, and many other types
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of content. The model `Map` is simply transformed into an appropriate format, such as
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JSP request attributes or a FreeMarker template model.
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[[mvc-features]]
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=== Features of Spring Web MVC
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.Spring Web Flow
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****
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Spring Web Flow (SWF) aims to be the best solution for the management of web application
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page flow.
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SWF integrates with existing frameworks like Spring MVC and JSF, in both Servlet and
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Portlet environments. If you have a business process (or processes) that would benefit
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from a conversational model as opposed to a purely request model, then SWF may be the
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solution.
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SWF allows you to capture logical page flows as self-contained modules that are reusable
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in different situations, and as such is ideal for building web application modules that
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guide the user through controlled navigations that drive business processes.
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For more information about SWF, consult the
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http://projects.spring.io/spring-webflow/[Spring Web Flow website].
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****
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Spring's web module includes many unique web support features:
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* __Clear separation of roles__. Each role -- controller, validator, command object,
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form object, model object, `DispatcherServlet`, handler mapping, view resolver, and so
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on -- can be fulfilled by a specialized object.
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* __Powerful and straightforward configuration of both framework and application classes
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as JavaBeans__. This configuration capability includes easy referencing across
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contexts, such as from web controllers to business objects and validators.
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* __Adaptability, non-intrusiveness, and flexibility.__ Define any controller method
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signature you need, possibly using one of the parameter annotations (such as
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@RequestParam, @RequestHeader, @PathVariable, and more) for a given scenario.
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* __Reusable business code, no need for duplication__. Use existing business objects
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as command or form objects instead of mirroring them to extend a particular framework
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base class.
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* __Customizable binding and validation__. Type mismatches as application-level
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validation errors that keep the offending value, localized date and number binding,
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and so on instead of String-only form objects with manual parsing and conversion to
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business objects.
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* __Customizable handler mapping and view resolution__. Handler mapping and view
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resolution strategies range from simple URL-based configuration, to sophisticated,
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purpose-built resolution strategies. Spring is more flexible than web MVC frameworks
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that mandate a particular technique.
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* __Flexible model transfer__. Model transfer with a name/value `Map` supports easy
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integration with any view technology.
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* __Customizable locale, time zone and theme resolution, support for JSPs with or without
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Spring tag library, support for JSTL, support for FreeMarker without the need for extra
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bridges, and so on.__
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* __A simple yet powerful JSP tag library known as the Spring tag library that provides
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support for features such as data binding and themes__. The custom tags allow for
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maximum flexibility in terms of markup code. For information on the tag library
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descriptor, see the appendix entitled <<appendix.adoc#spring-tld, Spring TLD>>
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* __A JSP form tag library, introduced in Spring 2.0, that makes writing forms in JSP
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pages much easier.__ For information on the tag library descriptor, see the appendix
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entitled <<appendix.adoc#spring-form-tld, Spring Form TLD>>
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* __Beans whose lifecycle is scoped to the current HTTP request or HTTP `Session`.__
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This is not a specific feature of Spring MVC itself, but rather of the
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`WebApplicationContext` container(s) that Spring MVC uses. These bean scopes are
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described in <<core.adoc#beans-factory-scopes-other, Request, session, application,
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and WebSocket scopes>>
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[[mvc-introduction-pluggability]]
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=== Pluggability of other MVC implementations
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Non-Spring MVC implementations are preferable for some projects. Many teams expect to
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leverage their existing investment in skills and tools, for example with JSF.
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If you do not want to use Spring's Web MVC, but intend to leverage other solutions that
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Spring offers, you can integrate the web MVC framework of your choice with Spring
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easily. Simply start up a Spring root application context through its
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`ContextLoaderListener`, and access it through its `ServletContext` attribute (or
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Spring's respective helper method) from within any action object. No "plug-ins"
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are involved, so no dedicated integration is necessary. From the web layer's point of
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view, you simply use Spring as a library, with the root application context instance as
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the entry point.
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Your registered beans and Spring's services can be at your fingertips even without
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Spring's Web MVC. Spring does not compete with other web frameworks in this scenario.
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It simply addresses the many areas that the pure web MVC frameworks do not, from bean
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configuration to data access and transaction handling. So you can enrich your
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application with a Spring middle tier and/or data access tier, even if you just want
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to use, for example, the transaction abstraction with JDBC or Hibernate.
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== Introduction to Spring Web MVC
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Spring Web MVC is the Servlet-based, web framework included in the Spring Framework.
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Its name is based on the name of the module, "spring-webmvc", but most people call
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it simply Spring MVC.
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The Spring Framework also includes the reactive, <<webflux,Spring WebFlux>>
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web framework that runs on on Servlet containers via Servlet 3.1 non-blocking I/O
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as well as on other non-blocking runtimes such as Netty and Undertow.
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[[mvc-servlet]]
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== The DispatcherServlet
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Spring's web MVC framework is, like many other web MVC frameworks, request-driven,
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designed around a central Servlet that dispatches requests to controllers and offers
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other functionality that facilitates the development of web applications. Spring's
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`DispatcherServlet` however, does more than just that. It is completely integrated with
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the Spring IoC container and as such allows you to use every other feature that Spring
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has.
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Spring MVC, like many other web frameworks, is designed around the front controller
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pattern with a central `Servlet`, the `DispatcherServlet`, dispatching incoming
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requests to registered handlers for processing requests, providing convenient mapping
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and exception handling facilities.
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The request processing workflow of the Spring Web MVC `DispatcherServlet` is illustrated
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in the following diagram. The pattern-savvy reader will recognize that the
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`DispatcherServlet` is an expression of the "Front Controller" design pattern (this is a
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pattern that Spring Web MVC shares with many other leading web frameworks).
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The `DispatcherServlet` provides the shared algorithm for processing requests while
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actual work is performed by configurable, delegate components. This model is very
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flexible and it can be used with just about any workflow, with the installation of the
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appropriate delegate components
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(see <<mvc-servlet-special-bean-types,Special Bean Types>>).
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.The request processing workflow in Spring Web MVC (high level)
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image::images/mvc.png[]
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The `DispatcherServlet` uses Spring configuration to discover the delegate components
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it needs to perform handler mapping, view resolution, and much more. As an actual
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`Servlet` it needs to be declared and mapped according to the Servlet specification.
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This can be done through code configuration or in`web.xml`.
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The `DispatcherServlet` is an actual `Servlet` (it inherits from the `HttpServlet` base
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class), and as such is declared in your web application. You need to map requests that
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you want the `DispatcherServlet` to handle, by using a URL mapping. Here is a standard
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Java EE Servlet configuration in a Servlet 3.0+ environment:
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Below is an example of code-based configuration where `WebApplicationInitializer` is an
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interface provided by Spring MVC that ensures this Java-based configuration is
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auto-detected by the Servlet container (see
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<<mvc-container-config,Code-based Servlet container initialization>> for more details):
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[source,java,indent=0]
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[subs="verbatim,quotes"]
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----
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public class MyWebApplicationInitializer implements WebApplicationInitializer {
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public class MyWebApplicationInitializer implements WebApplicationInitializer {
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@Override
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public void onStartup(ServletContext container) {
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ServletRegistration.Dynamic registration = container.addServlet("example", new DispatcherServlet());
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public void onStartup(ServletContext servletCxt) {
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// Load Spring web application configuration
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AnnotationConfigWebApplicationContext cxt = new AnnotationConfigWebApplicationContext();
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cxt.register(AppConfig.class);
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cxt.refresh();
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// Create DispatcherServlet
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DispatcherServlet servlet = new DispatcherServlet(cxt);
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// Register and map the Servlet
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ServletRegistration.Dynamic registration = servletCxt.addServlet("app", servlet);
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registration.setLoadOnStartup(1);
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registration.addMapping("/example/*");
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registration.addMapping("/app/*");
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}
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}
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}
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----
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In the preceding example, all requests starting with `/example` will be handled by the
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`DispatcherServlet` instance named `example`.
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In addition to using the ServletContext API directly as shown above, you can also extend
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the convenient base class `AbstractAnnotationConfigDispatcherServletInitializer` and
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override specific methods to customize it (an example is shown later under
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<<mvc-servlet-context-hierarchy,WebApplicationContext Hierarchy>>).
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`WebApplicationInitializer` is an interface provided by Spring MVC that ensures your
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code-based configuration is detected and automatically used to initialize any Servlet 3
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container. An abstract base class implementation of this interface named
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`AbstractAnnotationConfigDispatcherServletInitializer` makes it even easier to register the
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`DispatcherServlet` by simply specifying its servlet mapping and listing configuration
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classes - it's even the recommended way to set up your Spring MVC application.
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See <<mvc-container-config,Code-based Servlet container initialization>> for more details.
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The `DispatcherServlet` is an actual `Servlet` (it inherits from the `HttpServlet` base
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class), and as such is declared in the `web.xml` of your web application. You need to
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map requests that you want the `DispatcherServlet` to handle, by using a URL mapping in
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the same `web.xml` file. This is standard Java EE Servlet configuration; the following
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example shows such a `DispatcherServlet` declaration and mapping:
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Below is the `web.xml` equivalent of the above code based example:
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Below is the `web.xml` equivalent of the above code-based example:
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[source,xml,indent=0]
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[subs="verbatim,quotes"]
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----
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<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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<web-app>
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<servlet-mapping>
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<servlet-name>example</servlet-name>
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<url-pattern>/example/*</url-pattern>
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</servlet-mapping>
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<listener>
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<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
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</listener>
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</web-app>
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----
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As detailed in <<core.adoc#context-introduction,Additional Capabilities of the ApplicationContext>>,
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`ApplicationContext` instances in Spring can be scoped.
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In the Web MVC framework, each `DispatcherServlet` has its own `WebApplicationContext`,
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which inherits all the beans already defined in the root `WebApplicationContext`.
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The root `WebApplicationContext` should contain all the
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infrastructure beans that should be shared between your other contexts and Servlet
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instances. These inherited beans can be overridden in the servlet-specific
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scope, and you can define new scope-specific beans local to a given Servlet instance.
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.Typical context hierarchy in Spring Web MVC
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image::images/mvc-context-hierarchy.png[]
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Upon initialization of a `DispatcherServlet`, Spring MVC looks for a file named
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__[servlet-name]-servlet.xml__ in the `WEB-INF` directory of your web application and
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creates the beans defined there, overriding the definitions of any beans defined with
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the same name in the global scope.
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Consider the following `DispatcherServlet` Servlet configuration (in the `web.xml` file):
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[source,xml,indent=0]
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[subs="verbatim,quotes"]
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----
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<web-app>
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<servlet>
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<servlet-name>**golfing**</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>**golfing**</servlet-name>
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<url-pattern>/golfing/*</url-pattern>
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</servlet-mapping>
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</web-app>
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----
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With the above Servlet configuration in place, you will need to have a file called
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`/WEB-INF/golfing-servlet.xml` in your application; this file will contain all of your
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Spring Web MVC-specific components (beans). You can change the exact location of this
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configuration file through a Servlet initialization parameter (see below for details).
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It is also possible to have just one root context for single DispatcherServlet scenarios.
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.Single root context in Spring Web MVC
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image::images/mvc-root-context.png[]
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This can be configured by setting an empty contextConfigLocation servlet init parameter,
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as shown below:
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[source,xml,indent=0]
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[subs="verbatim,quotes"]
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----
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<web-app>
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<context-param>
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<param-name>contextConfigLocation</param-name>
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<param-value>/WEB-INF/root-context.xml</param-value>
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<param-value>/WEB-INF/app-context.xml</param-value>
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</context-param>
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<servlet>
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<servlet-name>dispatcher</servlet-name>
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<servlet-name>app</servlet-name>
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<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
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<init-param>
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<param-name>contextConfigLocation</param-name>
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@ -283,56 +93,108 @@ as shown below:
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</init-param>
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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>dispatcher</servlet-name>
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<url-pattern>/*</url-pattern>
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<servlet-name>app</servlet-name>
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<url-pattern>/app/*</url-pattern>
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</servlet-mapping>
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<listener>
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<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
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</listener>
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</web-app>
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</web-app>
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----
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The `WebApplicationContext` is an extension of the plain `ApplicationContext` that has
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[[mvc-servlet-context-hierarchy]]
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=== WebApplicationContext Hierarchy
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For many applications, a single `WebApplicationContext` is simple and sufficient.
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It is also possible to set up a context hierarchy where one root `WebApplicationContext`
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is shared across multiple `DispatcherServlet` (or other `Servlet`) instances each with
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its own `WebApplicationContext` configuration
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(see <<core.adoc#context-introduction,Additional Capabilities of the ApplicationContext>>
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for more details).
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The root `WebApplicationContext` contains infrastructure beans (e.g. data repositories,
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business services) that need to be shared across multiple Servlet instances. These beans
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are effectively inherited and can be overridden (re-declared) in the Servlet-specific
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context, which also contains beans local to the given `Servlet`.
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image::images/mvc-context-hierarchy.png[]
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[NOTE]
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====
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`WebApplicationContext` is an extension of the plain `ApplicationContext` that has
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some extra features necessary for web applications. It differs from a normal
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`ApplicationContext` in that it is capable of resolving themes (see
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<<mvc-themeresolver>>), and that it knows which Servlet it is associated with (by having
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a link to the `ServletContext`). The `WebApplicationContext` is bound in the
|
||||
`ServletContext`, and by using static methods on the `RequestContextUtils` class you can
|
||||
a link to the `ServletContext`). `WebApplicationContext` is bound to the
|
||||
`ServletContext` and by using static methods on the `RequestContextUtils` class you can
|
||||
always look up the `WebApplicationContext` if you need access to it.
|
||||
====
|
||||
|
||||
Note that we can achieve the same with java-based configurations:
|
||||
Below is an example of configuration that sets up a `WebApplicationContext` hierarchy:
|
||||
|
||||
[source,java,indent=0]
|
||||
[subs="verbatim,quotes"]
|
||||
----
|
||||
public class GolfingWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
|
||||
public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
|
||||
|
||||
@Override
|
||||
protected Class<?>[] getRootConfigClasses() {
|
||||
// GolfingAppConfig defines beans that would be in root-context.xml
|
||||
return new Class[] { GolfingAppConfig.class };
|
||||
return new Class[] { RootConfig.class };
|
||||
}
|
||||
|
||||
@Override
|
||||
protected Class<?>[] getServletConfigClasses() {
|
||||
// GolfingWebConfig defines beans that would be in golfing-servlet.xml
|
||||
return new Class[] { GolfingWebConfig.class };
|
||||
return new Class[] { App1Config.class };
|
||||
}
|
||||
|
||||
@Override
|
||||
protected String[] getServletMappings() {
|
||||
return new String[] { "/golfing/*" };
|
||||
return new String[] { "/app1/*" };
|
||||
}
|
||||
|
||||
}
|
||||
----
|
||||
|
||||
Below is the `web.xml` equivalent:
|
||||
|
||||
[source,xml,indent=0]
|
||||
[subs="verbatim,quotes"]
|
||||
----
|
||||
<web-app>
|
||||
|
||||
<listener>
|
||||
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
|
||||
</listener>
|
||||
|
||||
<context-param>
|
||||
<param-name>contextConfigLocation</param-name>
|
||||
<param-value>/WEB-INF/root-context.xml</param-value>
|
||||
</context-param>
|
||||
|
||||
<servlet>
|
||||
<servlet-name>app1</servlet-name>
|
||||
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
|
||||
<init-param>
|
||||
<param-name>contextConfigLocation</param-name>
|
||||
<param-value>/WEB-INF/app1-context.xml</param-value>
|
||||
</init-param>
|
||||
<load-on-startup>1</load-on-startup>
|
||||
</servlet>
|
||||
|
||||
<servlet-mapping>
|
||||
<servlet-name>app1</servlet-name>
|
||||
<url-pattern>/app1/*</url-pattern>
|
||||
</servlet-mapping>
|
||||
|
||||
</web-app>
|
||||
----
|
||||
|
||||
|
||||
|
||||
[[mvc-servlet-special-bean-types]]
|
||||
=== Special Bean Types In the WebApplicationContext
|
||||
|
||||
The Spring `DispatcherServlet` uses special beans to process requests and render the
|
||||
The `DispatcherServlet` uses special beans to process requests and render the
|
||||
appropriate views. These beans are part of Spring MVC. You can choose which special
|
||||
beans to use by simply configuring one or more of them in the `WebApplicationContext`.
|
||||
However, you don't need to do that initially since Spring MVC maintains a list of
|
||||
|
|
|
|||
Loading…
Reference in New Issue