mvc.xml

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<chapter id="mvc">
  <title>Web MVC framework</title>

  <section id="mvc-introduction">
    <title>Introduction to Spring Web MVC framework</title>

    <para>The Spring Web model-view-controller (MVC) framework is designed
    around a <classname>DispatcherServlet</classname> that dispatches requests
    to handlers, with configurable handler mappings, view resolution, locale
    and theme resolution as well as support for uploading files. The default
    handler is based on the <interfacename>@Controller</interfacename> and
    <interfacename>@RequestMapping</interfacename> annotations, offering a
    wide range of flexible handling methods. With the introduction of Spring
    3.0, the <interfacename>@Controller</interfacename> mechanism also allows
    you to create RESTful Web sites and applications, through the
    <interfacename>@PathVarariable</interfacename> annotation and other
    features.</para>

    <sidebar id="mvc-open-for-extension">
      <title><quote>Open for extension...</quote></title>

      <para>A key design principle in Spring Web MVC and in Spring in general
      is the <quote><emphasis>Open for extension, closed for
      modification</emphasis></quote> principle.</para>

      <para>Some methods in the core classes of Spring Web MVC are marked
      <literal>final</literal>. As a developer you cannot override these
      methods to supply your own behavior. This has not been done arbitrarily, but
      specifically with this principal in mind.</para>

      <para>For an explanation of this principle, refer to <emphasis>Expert
      Spring Web MVC and Web Flow</emphasis> by Seth Ladd and others;
      specifically see the section "A Look At Design," on page 117 of the
      first edition. Alternatively, see</para>

      <orderedlist>
        <listitem>
          <para><ulink
          url="http://www.objectmentor.com/resources/articles/ocp.pdf">Bob
          Martin, The Open-Closed Principle (PDF)</ulink></para>
        </listitem>
      </orderedlist>

      <para>You cannot add advice to final methods when you use Spring MVC.
      For example, you cannot add advice to the
      <literal>AbstractController.handleRequest()</literal> method. Refer to
      <xref linkend="aop-understanding-aop-proxies" /> for more information on
      AOP proxies and why you cannot add advice to final methods.</para>
    </sidebar>

    <para>In Spring Web MVC you can use any object as a command or
    form-backing object; you do not need to implement a framework-specific
    interface or base class. Spring's data binding is highly flexible: for
    example, it treats type mismatches as validation errors that can be
    evaluated by the application, not as system errors. Thus you need not
    duplicate your business objects' properties as simple, untyped strings in
    your form objects simply to handle invalid submissions, or to convert the
    Strings properly. Instead, it is often preferable to bind directly to your
    business objects.</para>

    <para>Spring's view resolution is extremely flexible. A
    <interfacename>Controller</interfacename> implementation can even write
    directly to the response stream. Typically, a
    <classname>ModelAndView</classname> instance consists of a view name and a
    model <interfacename>Map</interfacename>, which contains bean names and
    corresponding objects such as a command or form, which contain reference
    data. View name resolution is highly configurable, through bean names, a
    properties file, or your own <interfacename>ViewResolver</interfacename>
    implementation. The model (the M in MVC) is based on the
    <interfacename>Map</interfacename> interface, which allows for the
    complete abstraction of the view technology. You can integrate directly
    JSP, Velocity, or any other rendering technology. The model
    <interfacename>Map</interfacename> is simply transformed into an
    appropriate format, such as JSP request attributes or a Velocity template
    model.</para>

    <section id="mvc-features">
      <title>Features of Spring Web MVC<!--I moved Features of Spring Web MVC before Pluggability of other MVC implementations. You want to highlight your own imp. first.--></title>

      <!--Second line of sidebar refers to JSF; don't you mean JSP? Other refs in this context are to JSP. Also note, sidebar is read-only.-->

      <xi:include href="swf-sidebar.xml"
                  xmlns:xi="http://www.w3.org/2001/XInclude" />

      <para>Spring's web module includes many unique web support
      features:</para>

      <itemizedlist>
        <listitem>
          <para><emphasis>Clear separation of roles</emphasis>. Each role --
          controller, validator, command object, form object, model object,
          <classname>DispatcherServlet</classname>, handler mapping, view
          resolver, and so on -- can be fulfilled by a specialized
          object.</para>
        </listitem>

        <listitem>
          <para><emphasis>Powerful and straightforward configuration of both
          framework and application classes as JavaBeans</emphasis>. This
          configuration capability includes easy referencing across contexts,
          such as from web controllers to business objects and
          validators.</para>
        </listitem>

        <listitem>
          <para><emphasis>Adaptability, non-intrusiveness, and
          flexibility.</emphasis> Define any controller method signature you
          need, possibly using one of the parameter annotations (such as
          @RequestParam, @RequestHeader, @PathVariable, and more) for a given
          scenario.</para>
        </listitem>

        <listitem>
          <para><emphasis>Reusable business code</emphasis>,<emphasis> no need
          for duplication</emphasis>. Use existing business objects as command
          or form objects instead of mirroring them to extend a particular
          framework base class.</para>
        </listitem>

        <listitem>
          <para><emphasis>Customizable binding and validation</emphasis>. Type
          mismatches as application-level validation errors that keep the
          offending value, localized date and number binding, and so on
          instead of String-only form objects with manual parsing and
          conversion to business objects.</para>
        </listitem>

        <listitem>
          <para><emphasis>Customizable handler mapping and view
          resolution</emphasis>. Handler mapping and view resolution
          strategies range from simple URL-based configuration, to
          sophisticated, purpose-built resolution strategies. Spring is more
          flexible than web MVC frameworks that mandate a particular
          technique.</para>
        </listitem>

        <listitem>
          <para><emphasis>Flexible model transfer</emphasis>. Model transfer
          with a name/value <interfacename>Map</interfacename> supports easy
          integration with any view technology.</para>
        </listitem>

        <listitem>
          <para><emphasis>Customizable locale and theme resolution, support
          for JSPs with or without Spring tag library, support for JSTL,
          support for Velocity without the need for extra bridges, and so
          on.</emphasis></para>
        </listitem>

        <listitem>
          <para><emphasis>A simple yet powerful JSP tag library known as the
          Spring tag library that provides support for features such as data
          binding and themes</emphasis>. The custom tags allow for maximum
          flexibility in terms of markup code. For information on the tag
          library descriptor, see the appendix entitled <xref
          linkend="spring.tld" /></para>
        </listitem>

        <listitem>
          <para><emphasis>A JSP form tag library, introduced in Spring 2.0,
          that makes writing forms in JSP pages much easier.</emphasis>  For
          information on the tag library descriptor, see the appendix entitled
          <xref linkend="spring-form.tld" /></para>
        </listitem>

        <listitem>
          <para><emphasis>Beans whose lifecycle is scoped to the current HTTP
          request or HTTP <interfacename>Session</interfacename>.</emphasis>
          This is not a specific feature of Spring MVC itself, but rather of
          the <interfacename>WebApplicationContext</interfacename>
          container(s) that Spring MVC uses. These bean scopes are described
          in <xref linkend="beans-factory-scopes-other" /></para>
        </listitem>
      </itemizedlist>
    </section>

    <section id="mvc-introduction-pluggability">
      <title>Pluggability of other MVC implementations</title>

      <para>Non-Spring MVC implementations are preferable for some projects.
      Many teams expect to leverage their existing investment in skills and
      tools. A large body of knowledge and experience exist for the Struts
      framework. If you can abide Struts' architectural flaws, it can be a
      viable choice for the web layer; the same applies to WebWork and other
      web MVC frameworks.</para>

      <para>If you do not want to use Spring's web MVC, but intend to leverage
      other solutions that Spring offers, you can integrate the web MVC
      framework of your choice with Spring easily. Simply start up a Spring
      root application context through its
      <classname>ContextLoaderListener</classname>, and access it through
      its<!--Identify *its*. do you mean root application context's?-->
      <interfacename>ServletContext</interfacename> attribute (or Spring's
      respective helper method) from within a Struts or WebWork action. No
      "plug-ins" are involved, so no dedicated integration is necessary. From
      the web layer's point of view, you simply use Spring as a library, with
      the root application context instance as the entry point.</para>

      <para>Your registered beans and Spring's services can be at your
      fingertips even without Spring's Web MVC. Spring does not compete with
      Struts or WebWork in this scenario. It simply addresses the many areas
      that the pure web MVC frameworks do not, from bean configuration to data
      access and transaction handling. So you can enrich your application with
      a Spring middle tier and/or data access tier, even if you just want to
      use, for example, the transaction abstraction with JDBC or
      Hibernate.</para>
    </section>
  </section>

  <section id="mvc-servlet">
    <title>The <classname>DispatcherServlet</classname></title>

    <para>Spring's web MVC framework is, like many other web MVC frameworks,
    request-driven, designed around a central servlet that dispatches requests
    to controllers and offers other functionality that facilitates the
    development of web applications. Spring's
    <classname>DispatcherServlet</classname> however, does more than just
    that. It is completely integrated with the Spring IoC container and as
    such allows you to use every other feature that Spring has.</para>

    <para>The request processing workflow of the Spring Web MVC
    <classname>DispatcherServlet</classname> is illustrated in the following
    diagram. The pattern-savvy reader will recognize that the
    <classname>DispatcherServlet</classname> is an expression of the
    <quote>Front Controller</quote> design pattern (this is a pattern that
    Spring Web MVC shares with many other leading web frameworks).</para>

    <para><mediaobject>
        <imageobject role="fo">
          <imagedata align="center" fileref="images/mvc.png" format="PNG" />
        </imageobject>

        <imageobject role="html">
          <imagedata align="center" fileref="images/mvc.png" format="PNG" />
        </imageobject>

        <caption><para>The requesting processing workflow in Spring Web MVC
        (high level)</para></caption>
      </mediaobject></para>

    <para>The <classname>DispatcherServlet</classname> is an actual
    <interfacename>Servlet</interfacename> (it inherits from the
    <classname>HttpServlet</classname> base class), and as such is declared in
    the <literal>web.xml</literal> of your web application. You need to map
    requests that you want the <classname>DispatcherServlet</classname> to
    handle, by using a URL mapping in the same <literal>web.xml</literal>
    file. This is standard J2EE servlet configuration; the following example
    shows such a <classname>DispatcherServlet</classname> declaration and
    mapping:</para>

    <programlisting language="xml">&lt;web-app&gt;

    &lt;servlet&gt;
        &lt;servlet-name&gt;example&lt;/servlet-name&gt;
        &lt;servlet-class&gt;org.springframework.web.servlet.DispatcherServlet&lt;/servlet-class&gt;
        &lt;load-on-startup&gt;1&lt;/load-on-startup&gt;
    &lt;/servlet&gt;

    &lt;servlet-mapping&gt;
        &lt;servlet-name&gt;example&lt;/servlet-name&gt;
        &lt;url-pattern&gt;*.form&lt;/url-pattern&gt;
    &lt;/servlet-mapping&gt;

&lt;/web-app&gt;</programlisting>

    <para>In the preceding example, all requests ending with
    <literal>.form</literal> will be handled by the <literal>example</literal>
    <classname>DispatcherServlet</classname>. This is only the first step in
    setting up Spring Web MVC. <!--The discussion below is a little vague about what you're doing, when you do it, and what you're accomplishing. --><!-- Is the next step shown in the next example screen?-->You
    now need to configure the various beans used by the Spring Web MVC
    framework (over and above the <classname>DispatcherServlet</classname>
    itself).<!--See previous sentence.Add info to indicate where you find info that tells you how to configure beans for MVC framework. --><!--Next paragraph, so what are you telling them to *do* here? --></para>

    <para>As detailed in <xref linkend="context-introduction" />,
    <interfacename>ApplicationContext</interfacename> instances in Spring can
    be scoped. In the Web MVC framework, each
    <classname>DispatcherServlet</classname> has its own
    <interfacename>WebApplicationContext</interfacename>, which inherits all
    the beans already defined in the root
    <interfacename>WebApplicationContext</interfacename>. These inherited
    beans can be overridden in the servlet-specific scope, and
    you can define new scope-specific beans local to a given servlet
    instance.</para>

    <para><mediaobject>
        <imageobject role="fo">
          <imagedata align="center" fileref="images/mvc-contexts.gif"
                     format="GIF" />
        </imageobject>

        <imageobject role="html">
          <imagedata align="center" fileref="images/mvc-contexts.gif"
                     format="GIF" />
        </imageobject>

        <caption>Context hierarchy in Spring Web MVC</caption>
      </mediaobject></para>

    <para>Upon initialization of a <classname>DispatcherServlet</classname>,
    the framework <!--Spring MVC or Spring Framework?--><emphasis><emphasis>looks
    for a file named</emphasis>
    <literal>[servlet-name]-servlet.xml</literal></emphasis> in the
    <literal>WEB-INF</literal> directory of your web application and creates
    the beans defined there, overriding the definitions of any beans defined
    with the same name in the global scope.</para>

    <para>Consider the following <classname>DispatcherServlet</classname>
    servlet configuration (in the <literal>web.xml</literal> file):</para>

    <programlisting language="xml">&lt;web-app&gt;

    &lt;servlet&gt;
        &lt;servlet-name&gt;<emphasis role="bold">golfing</emphasis>&lt;/servlet-name&gt;
        &lt;servlet-class&gt;org.springframework.web.servlet.DispatcherServlet&lt;/servlet-class&gt;
        &lt;load-on-startup&gt;1&lt;/load-on-startup&gt;
    &lt;/servlet&gt;

    &lt;servlet-mapping&gt;
        &lt;servlet-name&gt;<emphasis role="bold">golfing</emphasis>&lt;/servlet-name&gt;
        &lt;url-pattern&gt;/golfing/*&lt;/url-pattern&gt;
    &lt;/servlet-mapping&gt;

&lt;/web-app&gt;</programlisting>

    <para>With the above servlet configuration in place, <!--Is this something you need to do (in above example)? -->you
    will need to have a file called <literal>/WEB-INF/</literal><emphasis
    role="bold">golfing</emphasis><literal>-servlet.xml</literal> in your application;
    this file will contain all of your Spring Web MVC-specific components
    (beans). You can change the exact location of this configuration file
    through a servlet initialization parameter (see below for details).
    </para>
    <!--See *where* for details? Give x-ref to section talks about how to change the location of the file through servlet init. param.-->

    <para>The <interfacename>WebApplicationContext</interfacename> is an
    extension of the plain <interfacename>ApplicationContext</interfacename>
    that has some extra features necessary for web applications. It differs
    from a normal <interfacename>ApplicationContext</interfacename> in that it
    is capable of resolving themes (see <xref linkend="mvc-themeresolver" />),
    and that it knows which servlet it is associated with (by having a link to
    the <interfacename>ServletContext</interfacename>). The
    <interfacename>WebApplicationContext</interfacename> is bound in the
    <interfacename>ServletContext</interfacename>, and by using static methods
    on the <classname>RequestContextUtils</classname> class you can always
    look up the <interfacename>WebApplicationContext</interfacename> if you
    need access to it.</para>

    <para>The Spring <classname>DispatcherServlet</classname> uses special
    beans to process requests and render the appropriate views. These beans
    are part of Spring Framework. You can configure them in the
    <interfacename>WebApplicationContext</interfacename>, just as you
    configure any other bean. However, for most beans, sensible defaults are
    provided so you initially do not need to configure them. <!--Which beans have defaults? What do you mean you *initially* don't need to configure them? What determines whether you need to and --><!--when, if not *initially*? In table below, indicate which are defaults, which have to be configured.-->These
    beans are described in the following table. </para>

    <table id="mvc-webappctx-special-beans-tbl">
      <title>Special beans in the
      <interfacename>WebApplicationContext</interfacename></title>

      <tgroup cols="2">
        <colspec colname="c1" colwidth="1*" />

        <colspec colname="c2" colwidth="4*" />

        <thead>
          <row>
            <entry>Bean type</entry>

            <entry>Explanation</entry>
          </row>
        </thead>

        <tbody>
          <row>
            <entry><link linkend="mvc-controller">controllers</link></entry>

            <entry>Form the <literal>C</literal> part of the MVC.<!--Need info about controller function as with others in this list.Reader knows what C stands for.--></entry>
          </row>

          <row>
            <entry><link linkend="mvc-handlermapping">handler
            mappings</link></entry>

            <entry>Handle the execution of a list of pre-processors and
            post-processors and controllers that will be executed if they
            match certain criteria (for example, a matching URL specified with
            the controller).</entry>
          </row>

          <row>
            <entry><link linkend="mvc-viewresolver">view
            resolvers</link></entry>

            <entry>Resolves view names to views.<!--If it's capable of resolving, just say *resolves*. Like above, handler mappings are capable of handling the execution, but you just say *handle the execution*--></entry>
          </row>

          <row>
            <entry> <link linkend="mvc-localeresolver">locale
            resolver</link></entry>

            <entry>A <link linkend="mvc-localeresolver">locale resolver</link>
            is a component capable of resolving the locale a client is using,
            in order to be able to offer internationalized views</entry>
          </row>

          <row>
            <entry>Theme resolver</entry>

            <entry>A <link linkend="mvc-themeresolver">theme resolver</link>
            is capable of resolving themes your web application can use, for
            example, to offer personalized layouts</entry>
          </row>

          <row>
            <entry>multipart file resolver</entry>

            <entry>Contains functionality to process file uploads from HTML
            forms.<!--Here and next one, why not just say processes file uploads, maps executions instead of *contains functionality to*?--></entry>
          </row>

          <row>
            <entry><link linkend="mvc-exceptionhandlers">handler exception
            resolvers</link></entry>

            <entry> Contains functionality to map exceptions to views or
            implement other more complex exception handling code.</entry>
          </row>
        </tbody>
      </tgroup>
    </table>

    <para>After you set up a <classname>DispatcherServlet</classname>, and a
    request comes in for that specific
    <classname>DispatcherServlet</classname>, the
    <classname>DispatcherServlet</classname> starts processing the request as
    follows:</para>

    <orderedlist>
      <listitem>
        <para>The <interfacename>WebApplicationContext</interfacename> is
        searched for and bound in the request as an attribute that the
        controller and other elements in the process can use. <!--Use to do *what*? Also revise to indicate *what* searches for the WebApplicationContext -->It
        is bound by default under the key
        <literal>DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE</literal>.</para>
      </listitem>

      <listitem>
        <para>The locale resolver is bound to the request to enable elements
        in the process to resolve the locale to use when processing the
        request (rendering the view, preparing data, and so on). If you do not
        need locale resolving, you do not need it.</para>
      <!--Reword 'if you don't need local resolving, you dont need to use it '. Are you saying locale resolving is optional? If you don't configure it, will this step occur?-->
      </listitem>

      <listitem>
        <para>The theme resolver is bound to the request to let elements such
        as views determine which theme to use. If you do not use themes, you
        can ignore it.</para>
      <!-- MLP perhaps say that there are not side effect to this binding.etc... Clarify *ignore it*. Does this step still occur if you don't use themes? --><!--And what if you DO use themes, what do you do and when? Same question re locale resolving.-->
      </listitem>

      <listitem>
        <para>If you specify a multipart file resolver, the request is
        inspected for multiparts; if multiparts are found, the request is
        wrapped in a <classname>MultipartHttpServletRequest</classname> for
        further processing by other elements in the process. (See <xref
        linkend="mvc-multipart-resolver" /> for further information about
        multipart handling).</para>
      </listitem>

      <listitem>
        <para>An appropriate handler is searched for. If a handler is found,
        the execution chain associated with the handler (preprocessors,
        postprocessors, and controllers) is executed in order to prepare a
        model or rendering.</para>
      </listitem>

      <listitem>
        <para>If a model is returned, the view is rendered. If no model is
        returned, (may be due to a preprocessor or postprocessor
        intercepting the request, perhaps for security reasons), no view is
        rendered, because the request could already have been fulfilled.</para>
    <!--fulfilled how and by what?-->
      </listitem>
    </orderedlist>

    <para>Handler exception resolvers that are declared in the
    <interfacename>WebApplicationContext</interfacename> pick up exceptions
    that are thrown during processing of the request. Using these exception
    resolvers allows you to define custom behaviors to address
    exceptions.</para>

    <para>The Spring <classname>DispatcherServlet</classname> also supports
    the return of the <emphasis>last-modification-date</emphasis>, as
    specified by the Servlet API. The process of determining the last
    modification date for a specific request is straightforward: the
    <classname>DispatcherServlet</classname> looks up an appropriate handler
    mapping and tests whether the handler that is found
    implements the
    <emphasis><interfacename>LastModified</interfacename></emphasis>
    interface. If so, the value of the <literal>long
    getLastModified(request)</literal> method of the
    <interfacename>LastModified</interfacename> interface is returned to the
    client.</para>

    <para>You can customize individual <classname>DispatcherServlet</classname>
      instances by adding servlet initialization parameters (<literal>init-param</literal> elements) 
       to the servlet declaration in the <literal>web.xml</literal> file. See the following table for the list
      of supported parameters.</para>
    <!--Reword above sentence to specify whether configuring parameters in table configures last-modification-date, or are they further -->
    <!--customization for some other purpose? If so, need to explain how you config last-modification-date-->

    <table id="mvc-disp-servlet-init-params-tbl">
      <title><classname>DispatcherServlet</classname> initialization
      parameters</title>

      <tgroup cols="2">
        <colspec colname="c1" colwidth="1*" />

        <colspec colname="c2" colwidth="4*" />

        <thead>
          <row>
            <entry>Parameter</entry>

            <entry>Explanation</entry>
          </row>
        </thead>

        <tbody>
          <row>
            <entry><literal>contextClass</literal></entry>

            <entry>Class that implements
            <interfacename>WebApplicationContext</interfacename>, which
            instantiates the context used by this servlet. By default, the
            <classname>XmlWebApplicationContext</classname> is used.</entry>
          </row>

          <row>
            <entry><literal>contextConfigLocation</literal></entry>

            <entry>String that is passed to the context instance (specified by
            <literal>contextClass</literal>) to indicate where context(s) can
            be found. The string consists potentially of multiple strings
            (using a comma as a delimiter) to support multiple contexts. In
            case of multiple context locations with beans that are defined
            twice, the latest location takes precedence.</entry>
            <!-- MLP review -->
          </row>

          <row>
            <entry><literal>namespace</literal></entry>

            <entry>Namespace of the
            <interfacename>WebApplicationContext</interfacename>. Defaults to
            <literal>[servlet-name]-servlet</literal>.</entry>
          </row>
        </tbody>
      </tgroup>
    </table>
  </section>

  <section id="mvc-controller">
    <title>Implementing Controllers</title>

    <para>Controllers provide access to the application behavior that you
    typically define through a service interface. <!--I changed preceding to active voice because next sentence refers to user input. Thus *you* do some defining.-->Controllers
    interpret user input and transform it into a model that is represented to
    the user by the view. Spring implements a controller in a very abstract
    way, which enables you to create a wide variety of controllers.</para>

    <para>Spring 2.5 introduced an annotation-based programming model for MVC
    controllers that uses annotations such as
    <interfacename>@RequestMapping</interfacename>,
    <interfacename>@RequestParam</interfacename>,
    <interfacename>@ModelAttribute</interfacename>, and so on. This annotation
    support is available for both Servlet MVC and Portlet MVC. Controllers
    implemented in this style do not have to extend specific base classes or
    implement specific interfaces. Furthermore, they do not usually have
    direct dependencies on Servlet or Portlet APIs, although you can easily
    configure access to Servlet or Portlet facilities.</para>

    <tip>
      <para>The Spring distribution ships with the
      <emphasis>PetClinic</emphasis> sample, a web application that leverages
      the annotation support described in this section, in the context of
      simple form processing. The <emphasis>PetClinic</emphasis> application
      resides in the <literal>org.springframework.samples.petclinic</literal> module.</para>

      <!-- MLP Note removed reference to imagedb -->
    </tip>

    <!--You need an intro sentence here that indicates the *purpose* of the following code.  -->

    <programlisting language="java">@Controller
public class HelloWorldController {

    @RequestMapping("/helloWorld")
    public ModelAndView helloWorld() {
        ModelAndView mav = new ModelAndView();
        mav.setViewName("helloWorld");
        mav.addObject("message", "Hello World!");
        return mav;
    }
}</programlisting>

    <para>As you can see, the <interfacename>@Controller</interfacename> and
    <interfacename>@RequestMapping</interfacename> annotations allow flexible
    method names and signatures. In this particular example the method has no
    parameters and returns a <classname>ModelAndView</classname>, but various
    other (and better) strategies exist, <!--strategies for doing *what*? -->as
    are explained later in this section. <classname>ModelAndView</classname>,
    <interfacename>@Controller</interfacename>, and
    <interfacename>@RequestMapping</interfacename> form the basis for the
    Spring MVC implementation. This section documents these annotations and
    how they are most commonly used in a Servlet environment.</para>

    <section id="mvc-ann-controller">
      <title>Defining a controller with
      <interfacename>@Controller</interfacename></title>

      <para>The <interfacename>@Controller</interfacename> annotation
      indicates that a particular class serves the role of a
      <emphasis>controller</emphasis>. Spring does not require you to extend
      any controller base class or reference the Servlet API. However, you can
      still reference Servlet-specific features if you need to.</para>

      <para>The <interfacename>@Controller</interfacename> annotation acts as
      a stereotype for the annotated class, indicating its role. The
      dispatcher scans such annotated classes for mapped methods and detects
      <interfacename>@RequestMapping</interfacename> annotations (see the next
      section).</para>

      <para>You can define annotated controller beans explicitly, using a
      standard Spring bean definition in the dispatcher's context. However,
      the <interfacename>@Controller</interfacename> stereotype also allows
      for autodetection, aligned with Spring general support for detecting
      component classes in the classpath and auto-registering bean definitions
      for them.</para>
     <!-- MLP Bev.changed to 'also supports autodetection -->
      <para>To enable autodetection of such annotated controllers, you add
      component scanning to your configuration. Use the
      <emphasis>spring-context</emphasis> schema as shown in the following XML
      snippet:</para>

      <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;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"&gt;

    &lt;context:component-scan base-package="org.springframework.samples.petclinic.web"/&gt;

    <lineannotation>// ...</lineannotation>

&lt;/beans&gt;</programlisting>
    </section>

    <section id="mvc-ann-requestmapping">
      <title>Mapping requests with
      <interfacename>@RequestMapping</interfacename></title>

      <para>You use the <interfacename>@RequestMapping</interfacename>
      annotation to map URLs such as <filename>/appointments</filename> onto
      an entire class or a particular handler method. 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 in a Spring MVC application
      that uses this annotation:</para>

      <programlisting language="java">@Controller
<emphasis role="bold">@RequestMapping("/appointments")</emphasis>
public class AppointmentsController {

    private final AppointmentBook appointmentBook;
    
    @Autowired
    public AppointmentsController(AppointmentBook appointmentBook) {
        this.appointmentBook = appointmentBook;
    }

    <emphasis role="bold">@RequestMapping(method = RequestMethod.GET)</emphasis>
    public Map&lt;String, Appointment&gt; get() {
        return appointmentBook.getAppointmentsForToday();
    }

    <emphasis role="bold">@RequestMapping(value="/{day}", method = RequestMethod.GET)</emphasis>
    public Map&lt;String, Appointment&gt; getForDay(@PathVariable @DateTimeFormat(iso=ISO.DATE) Date day, Model model) {
        return appointmentBook.getAppointmentsForDay(day);
    }

    <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 add(@Valid AppointmentForm appointment, BindingResult result) {
        if (result.hasErrors()) {
            return "appointments/new";
        }
        appointmentBook.addAppointment(appointment);
        return "redirect:/appointments";
    }
}</programlisting>

      <para>In the example, the <interfacename>@RequestMapping</interfacename>
      is used in a number of places. The first usage is on the type (class)
      level, which indicates that all handling methods on this controller are
      relative to the <filename>/appointments</filename> path. The
      <methodname>get()</methodname> method has a further
      <interfacename>@RequestMapping</interfacename> refinement: it only
      accepts GET requests, meaning that an HTTP GET for
      <filename>/appointments</filename> invokes this method. The
      <methodname>post()</methodname> has a similar refinement, and the
      <methodname>getNewForm()</methodname> combines the definition of HTTP
      method and path into one, so that GET requests for
      <filename>appointments/new</filename> are handled by that method.</para>

      <para>The <methodname>getForDay()</methodname> method shows another
      usage of <interfacename>@RequestMapping</interfacename>: URI templates.
      (See <link linkend="mvc-ann-requestmapping-uri-templates">the next
      section </link>).</para>

      <para>A <interfacename>@RequestMapping</interfacename> on the class
      level is not required. Without it, all paths are simply absolute, and
      not relative. The following example from the PetClinic sample
      application shows a multi-action controller using
      <classname>@RequestMapping</classname>:</para>

      <programlisting language="java">@Controller
public class ClinicController {

    private final Clinic clinic;

    @Autowired
    public ClinicController(Clinic clinic) {
        this.clinic = clinic;
    }

    <emphasis role="bold">@RequestMapping("/")</emphasis>
    public void welcomeHandler() {
    }

    <emphasis role="bold">@RequestMapping("/vets")</emphasis>
    public ModelMap vetsHandler() {
        return new ModelMap(this.clinic.getVets());
    }

}</programlisting>

      <section id="mvc-ann-requestmapping-uri-templates">
        <title>URI Templates</title>

        <para>To access parts of a request URL in your handling methods, use
        the <emphasis><emphasis>URI templates</emphasis></emphasis> in the
        <interfacename>@RequestMapping</interfacename> path value.</para>

        <sidebar id="mvc-uri-templates">
          <title>URI Templates</title>

          <para>A URI Template is a URI-like string, containing one or more
          variable names. When you substitute values for these variables, the
          template becomes a URI. The <ulink
          url="http://bitworking.org/projects/URI-Templates/">proposed
          RFC</ulink> for URI Templates defines how a URI is parameterized.
          For example, the URI Template</para>

          <programlisting>http://www.example.com/users/{userid}</programlisting>

          <para>contains the variable <emphasis>userid</emphasis>. If we
          assign the variable the value fred, the URI Template yields:</para>

          <programlisting>http://www.example.com/users/fred</programlisting>

          <para>During the processing of a request, the URI can be compared to
          an expected URI Template in order to extract a collection of
          variables.</para>
        </sidebar>

        <para>Use the <interfacename>@PathVariable</interfacename> method
        parameter annotation to indicate that a method parameter should be
        bound to the value of a URI template variable.</para>

        <para>The following code snippet shows the usage of a single
        <interfacename>@PathVariable</interfacename> in a controller
        method:</para>

        <programlisting language="java">@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
public String findOwner(<emphasis role="bold">@PathVariable</emphasis> String ownerId, Model model) {
  Owner owner = ownerService.findOwner(ownerId);  
  model.addAttribute("owner", owner);  
  return "displayOwner"; 
}
</programlisting>

        <para>The URI Template "<literal>/owners/{ownerId}</literal>"
        specifies the variable name <emphasis>ownerId</emphasis>. When the
        controller handles this request, the value of
        <emphasis>ownerId</emphasis> is set to the value in the request URI.
        For example, when a request comes in for /owners/fred, the value fred
        is bound to the method parameter <literal>String
        ownerId</literal>.</para>

        <!-- MLP: Bev Review -->
        <para>The matching of method parameter names to URI Template variable
        names can only be done if your code is compiled with debugging
        enabled. If you do have not debugging enabled, you must specify the
        name of the URI Template variable name in the @PathVariable annotation
        in order to bind the resolved value of the variable name to a 
        method parameter. For example:</para>

        <programlisting language="java">@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
public String findOwner(<emphasis role="bold">@PathVariable</emphasis>("ownerId") String ownerId, Model model) {
  // implementation omitted
}</programlisting>
    <para>
        You can also use a controller method with the following
        signature:</para>

        <programlisting language="java">@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
public String findOwner(<emphasis role="bold">@PathVariable</emphasis>("ownerId") String theOwner, Model model) {
  // implementation omitted
}</programlisting>

        <para>You can use multiple @PathVariable annotations to bind <!--specify: to bind *what* to multiple URI template variables? method parameter String ownerId?-->to
        multiple URI Template variables:</para>

        <programlisting language="java">@RequestMapping(value="/owners/{ownerId}/pets/{petId}", method=RequestMethod.GET)
public String findPet(<emphasis role="bold">@PathVariable</emphasis> String ownerId, <emphasis
            role="bold">@PathVariable</emphasis> String petId, Model model) {
  Owner owner = ownerService.findOwner(ownderId);  
  Pet pet = owner.getPet(petId);  
  model.addAttribute("pet", pet);  
  return "displayPet"; 
}
</programlisting>

        <para>The following code snippet shows the usage 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, etc. Spring automatically converts to the appropriate type and
          throws a <classname>TypeMismatchException</classname> if the type is
          not correct. You can further customize this conversion process by
          customizing the data binder. See <xref
          linkend="mvc-ann-webdatabinder" />.</para>
        </tip>
      </section>

      <section id="mvc-ann-requestmapping-advanced">
        <title>Advanced <interfacename>@RequestMapping</interfacename>
        options</title>

        <para>In addition to URI templates, the
        <interfacename>@RequestMapping</interfacename> annotation also
        supports Ant-style path patterns (for example,
        <filename>/myPath/*.do</filename>). A combination of URI templates and
        Ant-style globs is also supported (for example,
        <filename>/owners/*/pets/{petId}</filename>).</para>

        <para>The handler method names are taken into account for narrowing if
        no path was specified explicitly, according to the specified
        <interfacename>org.springframework.web.servlet.mvc.multiaction.MethodNameResolver</interfacename>
        (by default an
        <classname>org.springframework.web.servlet.mvc.multiaction.InternalPathMethodNameResolver</classname>).
        This only applies if annotation mappings do not specify a path mapping
        explicitly. In other words, the method name is only used for narrowing
        among a set of matching methods; it does not constitute a primary path
        mapping itself.</para>

        <para>If you have a single default method (without explicit path
        mapping), then all requests without a more specific mapped method
        found are dispatched to it. If you have multiple such default methods,
        then the method name is taken into account for choosing between
        them.</para>

        <para>You can narrow path mappings through parameter conditions: a
        sequence of "myParam=myValue" style expressions, with a request only
        mapped if each such parameter is found to have the given value. For
        example: <programlisting language="java">@Controller
@RequestMapping("/owners/{ownerId}")
public class RelativePathUriTemplateController {

  @RequestMapping(value = "/pets/{petId}", <emphasis role="bold">params="myParam=myValue"</emphasis>)
  public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {    
    // implementation omitted
  }
}
</programlisting> "myParam" style expressions are also supported, with such
        parameters having to be present in the request (allowed to have any
        value). <!--I don't understand the preceding sentence. Can you reword?-->Finally,
        "!myParam" style expressions indicate that the specified parameter is
        <emphasis>not</emphasis> supposed to be present in the request.</para>

        <para>Similarly, path mappings can be narrowed down through header
        conditions:</para>
        
        <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>

        <para>In the above example, the <methodname>addPet()</methodname> method is
        only invoked when the <literal>content-type</literal> matches the <literal>text/*</literal>
        pattern, for example, <literal>text/xml</literal>.</para>
      </section>

      <section id="mvc-ann-requestmapping-arguments">
        <title>Supported handler method arguments and return types</title>

        <para>Handler methods that are annotated with
        <classname>@RequestMapping</classname> can have very flexible
        signatures. They may have arguments of the following types, in
        arbitrary order (except for validation results, which need to follow
        right after the corresponding command object, if desired):
        <!--Reword preceding sentence to clarify, make it a complete sentence and no parentheses: first it says validation results *must*--><!--immediately follow command object, but then it says *if desired*. Clarify what must happen if what is desired. And are validation --><!-- results a type of argument? Relate to the sentence that precedes it.-->
        <itemizedlist>
            <listitem>
              <para>Request or response objects (Servlet API). Choose any
              specific request or response type, for example
              <interfacename>ServletRequest</interfacename> or
              <interfacename>HttpServletRequest</interfacename>.</para>
            </listitem>

            <listitem>
              <para>Session object (Servlet API): of type
              <interfacename>HttpSession</interfacename>. An argument of this
              type enforces the presence of a corresponding session. As a
              consequence, such an argument is never
              <literal>null</literal>.</para>

              <note>
                <para>Session access may not be thread-safe, in particular in
                a Servlet environment. Consider setting the
                <classname>AnnotationMethodHandlerAdapter</classname>'s
                "synchronizeOnSession" flag to "true" if multiple requests are
                allowed to access a session concurrently.</para>
              </note>
            </listitem>

            <listitem>
              <para><classname>org.springframework.web.context.request.WebRequest</classname>
              or
              <classname>org.springframework.web.context.request.NativeWebRequest</classname>.
              Allows for generic request parameter access as well as
              request/session attribute access, without ties to the native
              Servlet/Portlet API.</para>
            </listitem>

            <listitem>
              <para><classname>java.util.Locale</classname> for the current
              request locale, determined by the most specific locale resolver
              available, in effect, the configured
              <interfacename>LocaleResolver</interfacename> in a Servlet
              environment.</para>
            </listitem>

            <listitem>
              <para><classname>java.io.InputStream</classname> /
              <classname>java.io.Reader</classname> for access to the
              request's content. This value is the raw InputStream/Reader as
              exposed by the Servlet API.</para>
            </listitem>

            <listitem>
              <para><classname>java.io.OutputStream</classname> /
              <classname>java.io.Writer</classname> for generating the
              response's content. This value is the raw OutputStream/Writer as
              exposed by the Servlet API.</para>
            </listitem>

            <listitem>
              <para><classname>@PathVariabe</classname> annotated parameters
              for access to URI template variables. See <xref
              linkend="mvc-ann-requestmapping-uri-templates" />.</para>
            </listitem>

            <listitem>
              <para><classname>@RequestParam</classname> annotated parameters
              for access to specific Servlet request parameters. Parameter
              values are converted to the declared method argument type. See
              <xref linkend="mvc-ann-requestparam" />.</para>
            </listitem>

            <listitem>
              <para><classname>@RequestHeader</classname> annotated parameters
              for access to specific Servlet request HTTP headers. Parameter
              values are converted to the declared method argument
              type.</para>
            </listitem>

            <listitem>
              <para><classname>@RequestBody</classname> annotated parameters
              for access to the HTTP request body. Parameter values are
              converted to the declared method argument type using
              <interfacename>HttpMessageConverter</interfacename>s. See <xref
              linkend="mvc-ann-requestbody" />.</para>
            </listitem>

            <listitem>
              <para><interfacename>java.util.Map</interfacename> /
              <interfacename>org.springframework.ui.Model</interfacename> /
              <classname>org.springframework.ui.ModelMap</classname> for
              enriching the implicit model that is exposed to the web
              view.</para>
            </listitem>

            <listitem>
              <para>Command or form objects to bind parameters to: as bean
              properties or fields, <!--What do you mean by *as bean properties or fields*, what does that refer to? Why do you have a colon? Don't get this line.--><!--*to bind parameters to* is awkward. Avoid slashes as with *command/form objects*. Do you mean command or form objects? Revise.-->with
              customizable type conversion, depending on
              <classname>@InitBinder</classname> methods and/or the
              HandlerAdapter configuration. See the
              <literal>webBindingInitializer</literal> property on
              <classname>AnnotationMethodHandlerAdapter</classname>. Such
              command objects along with their validation results will be
              exposed as model attributes by default, using the non-qualified
              command class name in property notation. <!--Who or what uses the non-qualified class name in property notation? Is this something you have to set up?-->For
              example, "orderAddress" for type "mypackage.OrderAddress".
              Specify a parameter-level <classname>ModelAttribute</classname>
              annotation for declaring a specific model attribute name.</para>
            </listitem>

            <listitem>
              <para><classname>org.springframework.validation.Errors</classname>
              /
              <classname>org.springframework.validation.BindingResult</classname>
              validation results for a preceding command or form object (the
              immediately preceding method argument).</para>
            </listitem>

            <listitem>
              <para><classname>org.springframework.web.bind.support.SessionStatus</classname>
              status handle for marking form processing as complete, which
              triggers the cleanup of session attributes that have been
              indicated by the <classname>@SessionAttributes</classname>
              annotation at the handler type level.</para>
            </listitem>
          </itemizedlist></para>

        <para>The following return types are supported for handler methods:
        <itemizedlist>
            <listitem>
              <para>A <classname>ModelAndView</classname> object, with the
              model implicitly enriched with command objects and the results
              of <literal>@ModelAttribute</literal> annotated reference data
              accessor methods.</para>
            </listitem>

            <listitem>
              <para>A <interfacename>Model</interfacename> object, with the
              view name implicitly determined through a
              <interfacename>RequestToViewNameTranslator</interfacename> and
              the model implicitly enriched with command objects and the
              results of <literal>@ModelAttribute</literal> annotated
              reference data accessor methods.</para>
            </listitem>

            <listitem>
              <para>A <interfacename>Map</interfacename> object for exposing a
              model, with the view name implicitly determined through a
              <interfacename>RequestToViewNameTranslator</interfacename> and
              the model implicitly enriched with command objects and the
              results of <literal>@ModelAttribute</literal> annotated
              reference data accessor methods.</para>
            </listitem>

            <listitem>
              <para>A <interfacename>View</interfacename> object, with the
              model implicitly determined through command objects and
              <literal>@ModelAttribute</literal> annotated reference data
              accessor methods. The handler method may also programmatically
              enrich the model by declaring a
              <interfacename>Model</interfacename> argument (see above).<!--see above where? Need more explicit reference. same problem with next item.--></para>
            </listitem>

            <listitem>
              <para>A <classname>String</classname> value that is interpreted
              as the logical view name, with the model implicitly determined through
              command objects and <literal>@ModelAttribute</literal> annotated
              reference data accessor methods. The handler method may also
              programmatically enrich the model by declaring a
              <interfacename>Model</interfacename> argument (see
              above).</para>
            </listitem>

            <listitem>
              <para><literal>void</literal> if the method handles the response
              itself (by writing the response content directly, declaring an
              argument of type <interfacename>ServletResponse</interfacename>
              / <interfacename>HttpServletResponse</interfacename> for that
              purpose) or if the view name is supposed to be implicitly
              determined through a
              <interfacename>RequestToViewNameTranslator</interfacename> (not
              declaring a response argument in the handler method
              signature).</para>
            </listitem>

            <listitem>
              <para>If the method is annotated with
              <interfacename>@ResponseBody</interfacename>, the return type is
              written to the response HTTP body. The return value will be
              converted to the declared method argument type using
              <interfacename>HttpMessageConverter</interfacename>s. See <xref
              linkend="mvc-ann-responsebody" />.</para>
            </listitem>

            <listitem>
              <para>Any other return type is considered to be a single model
              attribute to be exposed to the view, using the attribute name
              specified through <literal>@ModelAttribute</literal> at the
              method level (or the default attribute name based on the return
              type class name). The model is implicitly enriched with command
              objects and the results of <literal>@ModelAttribute</literal>
              annotated reference data accessor methods.</para>
            </listitem>
          </itemizedlist></para>
      </section>

      <section id="mvc-ann-requestparam">
        <title>Binding request parameters to method parameters with
        <classname>@RequestParam</classname></title>

        <para>Use the <classname>@RequestParam</classname> annotation to bind
        request parameters to a method parameter in your controller.</para>

        <para>The following code snippet shows the usage:</para>

        <programlisting language="java">@Controller
@RequestMapping("/pets")
@SessionAttributes("pet")
public class EditPetForm {

    <lineannotation>// ...</lineannotation>

    @RequestMapping(method = RequestMethod.GET)
    public String setupForm(<emphasis role="bold">@RequestParam("petId") int petId</emphasis>, ModelMap model) {
        Pet pet = this.clinic.loadPet(petId);
        model.addAttribute("pet", pet);
        return "petForm";
    }

    <lineannotation>// ...</lineannotation>
</programlisting>

        <para>Parameters using this annotation are required by default, but
        you can specify that a parameter is optional by setting
        <interfacename>@RequestParam</interfacename>'s
        <literal>required</literal> attribute to <literal>false</literal>
        (e.g., <literal>@RequestParam(value="id",
        required=false)</literal>).</para>
      </section>

      <section id="mvc-ann-requestbody">
        <title>Mapping the request body with the @RequestBody
        annotation</title>

        <para>The <classname>@RequestBody</classname> method parameter
        annotation indicates that a method parameter should be bound to the
        value of the HTTP request body. For example:</para>

        <programlisting language="java">@RequestMapping(value = "/something", method = RequestMethod.PUT)
public void handle(@RequestBody String body, Writer writer) throws IOException {
  writer.write(body);
}</programlisting>

        <para>You convert the request body to the method argument by using an
        <interfacename>HttpMessageConverter</interfacename>.
        <interfacename>HttpMessageConverter</interfacename> is responsible for
        converting from the HTTP request message to an object and converting
        from an object to the HTTP response body.
        <classname>DispatcherServlet</classname> supports annotation based
        processing using the
        <classname>DefaultAnnotationHandlerMapping</classname> and
        <classname>AnnotationMethodHandlerAdapter</classname>. In Spring 3.0
        the <classname>AnnotationMethodHandlerAdapter</classname> is extended
        to support the <classname>@RequestBody</classname> and has the
        following <interfacename>HttpMessageConverters</interfacename>
        registered by default:</para>

        <itemizedlist>
          <listitem>
            <para><classname>ByteArrayHttpMessageConverter</classname>
            converts byte arrays.</para>
          </listitem>

          <listitem>
            <para><classname>StringHttpMessageConverter</classname> converts
            strings.</para>
          </listitem>

          <listitem>
            <para><classname>FormHttpMessageConverter</classname> converts
            form data to/from a MultiValueMap&lt;String, String&gt;.</para>
          </listitem>

          <listitem>
            <para><classname>SourceHttpMessageConverter</classname> converts
            to/from a javax.xml.transform.Source.</para>
          </listitem>

          <listitem>
            <para><classname>MarshallingHttpMessageConverter</classname>
            converts to/from an object using the
            <classname>org.springframework.oxm</classname> package.</para>
          </listitem>
        </itemizedlist>

        <para>For more information on these converters, see <link
        linkend="rest-message-conversion">Message Converters</link>.</para>

        <para>The <classname>MarshallingHttpMessageConverter</classname>
        requires a <interfacename>Marshaller</interfacename> and
        <interfacename>Unmarshaller</interfacename> from the
        <classname>org.springframework.oxm</classname> package to be
        configured on an instance of
        <classname>AnnotationMethodHandlerAdapter</classname> in the
        application context. For example:</para>

        <programlisting language="xml">&lt;bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"&gt;
    &lt;property name="messageConverters"&gt;
      &lt;util:list id="beanList"&gt;
        &lt;ref bean="stringHttpMessageConverter"/&gt;
        &lt;ref bean="marshallingHttpMessageConverter"/&gt;
      &lt;/util:list&gt;
    &lt;/property
&lt;/bean&gt;

&lt;bean id="stringHttpMessageConverter" 
       class="org.springframework.http.converter.StringHttpMessageConverter"/&gt;

&lt;bean id="marshallingHttpMessageConverter" 
      class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter"&gt;
  &lt;property name="marshaller" ref="castorMarshaller" /&gt;
  &lt;property name="unmarshaller" ref="castorMarshaller" /&gt;
&lt;/bean&gt;

&lt;bean id="castorMarshaller" class="org.springframework.oxm.castor.CastorMarshaller"/&gt;
</programlisting>
      </section>

      <section id="mvc-ann-responsebody">
        <title>Mapping the response body with the @ResponseBody
        annotation</title>

        <para>The <interfacename>@ResponseBody</interfacename> annotation is
        similar to <interfacename>@RequestBody</interfacename>. This
        annotation can be put on a method <!--Revise *can be put on*. You do *what* with this annotation in regard to a method?-->and
        indicates that the return type should be written straight to the HTTP
        response body (and not placed in a Model, or interpreted as a view
        name). For example:</para>

        <programlisting language="java">@RequestMapping(value = "/something", method = RequestMethod.PUT)
@ResponseBody
public String helloWorld()  {
  return "Hello World";
}</programlisting>

        <para>The above example will result in the text <literal>Hello
        World</literal> being written to the HTTP response stream.</para>

        <para>As with <interfacename>@RequestBody</interfacename>, Spring converts
        the returned object to a response body by using an
        <interfacename>HttpMessageConverter</interfacename>. For more
        information on these converters, see the previous section and <link
        linkend="rest-message-conversion">Message Converters</link>.</para>
      </section>

      <section id="mvc-ann-modelattrib">
        <title>Providing a link to data from the model with
        <classname>@ModelAttribute</classname></title>

        <para><classname>@ModelAttribute</classname> has two usage scenarios
        in controllers. When you map it to <!--is this correct, *map it to*? If not, what do you mean by *is placed on*?-->a
        method parameter, <classname>@ModelAttribute</classname> maps a model
        attribute to the specific, annotated method parameter (see the
        <literal>processSubmit()</literal> method below). This is how the
        controller gets a reference to the object holding the data entered in
        the form.</para>

        <para>You can also use <classname>@ModelAttribute</classname> at
        the method level to provide <emphasis>reference data</emphasis> for
        the model (see the <literal>populatePetTypes()</literal> method in
        the following example). For this usage the method signature can contain
        the same types as documented previously for the
        <classname>@RequestMapping</classname> annotation.</para>

        <note>
          <para><classname>@ModelAttribute</classname> annotated methods are
          executed <emphasis>before</emphasis> the chosen
          <classname>@RequestMapping</classname> annotated handler method.
          They effectively pre-populate the implicit model with specific
          attributes, often loaded from a database. Such an attribute can then
          already be accessed through <classname>@ModelAttribute</classname>
          annotated handler method parameters in the chosen handler method,
          potentially with binding and validation applied to it.</para>
        </note>

        <para>The following code snippet shows these two usages of this
        annotation:</para>

        <programlisting language="java">@Controller
@RequestMapping("/owners/{ownerId}/pets/{petId}/edit")
@SessionAttributes("pet")
public class EditPetForm {

    <lineannotation>// ...</lineannotation>

    <emphasis role="bold">@ModelAttribute("types")</emphasis>
    public Collection&lt;PetType&gt; 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 or types 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, specifying the model attribute name:</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 demonstrates how to get the value of
        the <literal>JSESSIONID</literal> 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 sample request header:</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 demonstrates how to get the value of
        the <literal>Accept-Encoding</literal> and <literal>Keep-Alive</literal> headers:</para>

        <programlisting language="java">@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(<emphasis role="bold">@RequestHeader("Accept-Encoding")</emphasis> String encoding,
                              <emphasis role="bold">@RequestHeader("Keep-Alive")</emphasis> long keepAlive)  {

  //...

}</programlisting>

        <para>This annotation is supported for annotated handler methods in
        Servlet and Portlet environments.</para>
      </section>

      <section id="mvc-ann-webdatabinder">
        <title>Customizing <classname>WebDataBinder</classname>
        initialization</title>

        <para>To customize request parameter binding with PropertyEditors
        through Spring's <classname>WebDataBinder</classname>, you can use
        either <interfacename>@InitBinder</interfacename>-annotated methods
        within your controller or externalize your configuration by providing
        a custom <interfacename>WebBindingInitializer</interfacename>.</para>

        <section id="mvc-ann-initbinder">
          <title>Customizing data binding with
          <interfacename>@InitBinder</interfacename></title>

          <para>Annotating controller methods with
          <interfacename>@InitBinder</interfacename> allows you to configure
          web data binding directly within your controller class.
          <interfacename>@InitBinder</interfacename> identifies methods that
          initialize the <classname>WebDataBinder</classname> that will be
          used to populate command and form object arguments of annotated
          handler methods.</para>

          <para>Such init-binder methods support all arguments that
          <interfacename>@RequestMapping</interfacename> supports, except for
          command/form objects and corresponding validation result objects.
          Init-binder methods must not have a return value. Thus, they are
          usually declared as <literal>void</literal>. Typical arguments
          include <classname>WebDataBinder</classname> in combination with
          <interfacename>WebRequest</interfacename> or
          <classname>java.util.Locale</classname>, allowing code to register
          context-specific editors.</para>

          <para>The following example demonstrates the use of
          <interfacename>@InitBinder</interfacename> to configure a
          <classname>CustomDateEditor</classname> for all
          <classname>java.util.Date</classname> form properties.</para>

          <programlisting language="java">@Controller
public class MyFormController {

    <emphasis role="bold">@InitBinder</emphasis>
    public void initBinder(WebDataBinder binder) {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        dateFormat.setLenient(false);
        binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
    }

    <lineannotation>// ...</lineannotation>
}</programlisting>
        </section>

        <section id="mvc-ann-webbindinginitializer">
          <title>Configuring a custom
          <interfacename>WebBindingInitializer</interfacename></title>

          <para>To externalize data binding initialization, you can provide a
          custom implementation of the
          <interfacename>WebBindingInitializer</interfacename> interface,
          which you then enable by supplying a custom bean configuration for
          an <classname>AnnotationMethodHandlerAdapter</classname>, thus
          overriding the default configuration.</para>

          <para>The following example from the PetClinic application shows a
          configuration using a custom implementation of the
          <interfacename>WebBindingInitializer</interfacename> interface,
          <classname>org.springframework.samples.petclinic.web.ClinicBindingInitializer</classname>,
          which configures PropertyEditors required by several of the
          PetClinic controllers.</para>

          <programlisting language="xml">&lt;bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"&gt;
    &lt;property name="cacheSeconds" value="0" /&gt;
    &lt;property name="webBindingInitializer"&gt;
        &lt;bean class="org.springframework.samples.petclinic.web.ClinicBindingInitializer" /&gt;
    &lt;/property&gt;
&lt;/bean&gt;
</programlisting>
        </section>
      </section>
    </section>
  </section>

  <section id="mvc-handlermapping">
    <title>Handler mappings</title>

    <para>In previous versions of Spring, users were required to define
    <interfacename>HandlerMapping</interfacename>s in the web application
    context to map incoming web requests to appropriate handlers. With the
    introduction of Spring 2.5, <!--IMPORTANT: Shouldn't that say Spring 3.0, since that's upcoming release? If you do mean 2.5, then first sentence should say in pre--><!--2.5 versions of Spring, not *previous*. Also in first sentence, I changed Spring MVC to Spring because it refers to a version.-->the
    <classname>DispatcherServlet</classname> enables the
    <classname>DefaultAnnotationHandlerMapping</classname>, which looks for
    <interfacename>@RequestMapping</interfacename> annotations on
    <interfacename>@Controllers</interfacename>. Typically, you do not need to
    override this default mapping, unless you need to override the default property values.
    These properties are:</para>

	<variablelist>
		<varlistentry>
			<term><literal>interceptors</literal></term>
			<listitem>
				<para>
					List of interceptors to use.
					<interfacename>HandlerInterceptor</interfacename>s are discussed in
					<xref linkend="mvc-handlermapping-interceptor" />.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term><literal>defaultHandler</literal></term>
			<listitem>
				<para>Default handler to use, when this handler mapping does not result
				in a matching handler.</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term><literal>order</literal></term>
			<listitem>
				<para>
					Based on the value of the order property (see the
					<literal>org.springframework.core.Ordered</literal>
					interface), Spring sorts all handler mappings available in the context
					and applies the first matching handler.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term><literal>alwaysUseFullPath</literal></term>
			<listitem>
				<para>
					If <literal>true</literal> , Spring uses the full path within the current
					servlet context to find an appropriate handler. If <literal>false</literal>
					(the default), the path within the current servlet mapping is used. For
					example, if a servlet is mapped using <literal>/testing/*</literal>
					and the <literal>alwaysUseFullPath</literal> property is set to true,
					<literal>/testing/viewPage.html</literal> is used, whereas if the
					property is set to false, <literal>/viewPage.html</literal> is used.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term><literal>urlDecode</literal></term>
			<listitem>
				<para>
					Defaults to <literal>true</literal>, as of Spring 2.5. <!--OK, or do you mean 3.0?-->
					If you prefer to compare encoded paths, set this flag to <literal>false</literal>.
					However, the <interfacename>HttpServletRequest</interfacename> always exposes the
					servlet path in decoded form. Be aware that the servlet path will not match when
					compared with encoded paths.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term><literal>lazyInitHandlers</literal></term>
			<listitem>
				<para>
					Allows lazy initialization of <emphasis>singleton</emphasis>
					handlers (prototype handlers are always lazy-initialized).
					The default value is <literal>false</literal>.
				</para>
			</listitem>
		</varlistentry>
	</variablelist>

	<note>
		<para>
			The <literal>alwaysUseFullPath</literal>, <literal>urlDecode</literal>, and
			<literal>lazyInitHandlers</literal> properties are only available to subclasses of
			<interfacename>org.springframework.web.servlet.handler.AbstractUrlHandlerMapping</interfacename>.
		</para>
	</note>

    <para>The following example shows how to override the default mapping and
    add an interceptor:</para>

    <programlisting language="xml">&lt;beans&gt;
  &lt;bean id="handlerMapping" class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping"&gt;
    &lt;property name="interceptors"&gt;
      &lt;bean class="example.MyInterceptor"/&gt;
    &lt;/property&gt;
  &lt;/bean&gt;

&lt;beans&gt;</programlisting>

    <section id="mvc-handlermapping-interceptor">
      <title>Intercepting requests - the
      <interfacename>HandlerInterceptor</interfacename> interface<!--Revise head to delete dash. How should it read? Intercepting requests *through* the HandlerInterceptor Interface? *with*?--></title>

      <para>Spring's handler mapping mechanism includes handler interceptors,
      which are useful when you want to apply specific functionality to
      certain requests, for example, checking for a principal.</para>

      <para>Interceptors located in the handler mapping must implement
      <interfacename>HandlerInterceptor</interfacename> from the
      <literal>org.springframework.web.servlet</literal> package. This
      interface defines three methods: one is called
      <emphasis>before</emphasis> the actual handler is executed; one is
      called <emphasis>after</emphasis> the handler is executed; and one is
      called <emphasis>after the complete request has finished</emphasis>.
      <!--I suggest identifying each method in parentheses after the reference to it, in sentence above. -->These
      three methods should provide enough flexibility to do all kinds of
      preprocessing and postprocessing.</para>

      <para>The <literal>preHandle(..)</literal> method returns a boolean
      value. You can use this method to break or continue the processing of
      the execution chain. When this method returns <literal>true</literal>,
      the handler execution chain will continue; when it returns false, the
      <classname>DispatcherServlet</classname> assumes the interceptor itself
      has taken care of requests (and, for example, rendered an appropriate
      view) and does not continue executing the other interceptors and the
      actual handler in the execution chain.</para>

      <para>The following example defines a handler mapping which maps
        all requests matching the URL patterns "/*.form" and "/*.view" to a particular
        controller, <literal>editAccountFormController</literal>. 
         An interceptor has been added that intercepts these
      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">&lt;beans&gt;
    &lt;bean id="handlerMapping"
          class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"&gt;
        &lt;property name="interceptors"&gt;
            &lt;list&gt;
                &lt;ref bean="officeHoursInterceptor"/&gt;
            &lt;/list&gt;
        &lt;/property&gt;
        &lt;property name="mappings"&gt;
            &lt;value&gt;
                /*.form=editAccountFormController
                /*.view=editAccountFormController
            &lt;/value&gt;
        &lt;/property&gt;
    &lt;/bean&gt;

    &lt;bean id="officeHoursInterceptor"
          class="samples.TimeBasedAccessInterceptor"&gt;
        &lt;property name="openingTime" value="9"/&gt;
        &lt;property name="closingTime" value="18"/&gt;
    &lt;/bean&gt;
&lt;beans&gt;</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 &lt;= hour &lt; closingTime) {
            return true;
        } else {
            response.sendRedirect("http://host.com/outsideOfficeHours.html");
            return false;
        }
    }
}</programlisting>

      <para>Any request handled by this mapping is intercepted by the
      <classname>TimeBasedAccessInterceptor</classname>. If the current time
      is outside office hours, the user is redirected to a static HTML file
      that says, for example, you can only access the website during office
      hours.</para>

      <para>As you can see, the Spring adapter class
      <classname>HandlerInterceptorAdapter</classname> makes it easier to
      extend the <interfacename>HandlerInterceptor</interfacename>
      interface.</para>
    </section>
  </section>

  <section id="mvc-viewresolver">
    <title>Resolving views</title>

    <para>All MVC frameworks for web applications provide a way to address
    views. Spring provides view resolvers, which enable you to render models
    in a browser without tying you to a specific view technology. Out of the
    box, Spring enables you to use JSPs, Velocity templates and XSLT views,
    for example. See <xref linkend="view" /> for a discussion of how to
    integrate and use a number of disparate view technologies.</para>

    <para>The two interfaces that are important to the way Spring handles
    views are <interfacename>ViewResolver</interfacename> and
    <interfacename>View</interfacename>. The
    <interfacename>ViewResolver</interfacename> provides a mapping between
    view names and actual views. The <interfacename>View</interfacename>
    interface addresses the preparation of the request and hands the request
    over to one of the view technologies.</para>

    <section id="mvc-viewresolver-resolver">
      <title>Resolving views with the
      <interfacename>ViewResolver</interfacename> interface</title>

      <para>As discussed in <xref linkend="mvc-controller" />, all handler
      methods in the Spring Web MVC controllers must resolve to a logical
      view name, either explicitly (e.g., by returning a <literal>String</literal>,
      <literal>View</literal>, or <literal>ModelAndView</literal>) or implicitly
      (i.e., based on conventions). Views in Spring are
      addressed by a logical view name and are resolved by a view resolver. Spring
      comes with quite a few view resolvers. This table lists most of them; a
      couple of examples follow.</para>

      <table id="mvc-view-resolvers-tbl">
        <title>View resolvers</title>

        <tgroup cols="2">
          <colspec colname="c1" colwidth="1*" />

          <colspec colname="c2" colwidth="2*" />

          <thead>
            <row>
              <entry><interfacename>ViewResolver</interfacename></entry>

              <entry>Description</entry>
            </row>
          </thead>

          <tbody>
            <row>
              <entry><classname>AbstractCachingViewResolver</classname></entry>

              <entry>Abstract view resolver that caches views. Often views
              need preparation before they can be used; extending this view
              resolver provides caching.</entry>
            </row>

            <row>
              <entry><classname>XmlViewResolver</classname></entry>

              <entry>Implementation of
              <interfacename>ViewResolver</interfacename> that accepts a
              configuration file written in XML with the same DTD as Spring's
              XML bean factories. The default configuration file is
              <literal>/WEB-INF/views.xml</literal>.</entry>
            </row>

            <row>
              <entry><classname>ResourceBundleViewResolver</classname></entry>

              <entry>Implementation of
              <interfacename>ViewResolver</interfacename> that uses bean
              definitions in a <classname>ResourceBundle</classname>,
              specified by the bundle base name. Typically you define the
              bundle in a properties file, located in the classpath. <!--Correct to say you define? Seems so, because default implies you can change it.-->The
              default file name is
              <literal>views.properties</literal>.</entry>
            </row>

            <row>
              <entry><classname>UrlBasedViewResolver</classname></entry>

              <entry>Simple implementation of the
              <interfacename>ViewResolver</interfacename> interface that
              effects the direct resolution of logical view names to URLs,
              without an explicit mapping definition. This is appropriate if
              your logical 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>Convenient subclass of
              <classname>UrlBasedViewResolver</classname> that supports
              <classname>InternalResourceView</classname> (in effect, Servlets
              and JSPs) and subclasses such as
              <classname>JstlView</classname> and
              <classname>TilesView</classname>. You can specify the view class
              for all views generated by this resolver by using
              <literal>setViewClass(..)</literal>. See the Javadocs for the
              <classname>UrlBasedViewResolver</classname> class for
              details.</entry>
            </row>

            <row>
              <entry><classname>VelocityViewResolver</classname> /
              <classname>FreeMarkerViewResolver</classname></entry>

              <entry>Convenient subclass of
              <classname>UrlBasedViewResolver</classname> that supports
              <classname>VelocityView</classname> (in effect, Velocity
              templates) or <classname>FreeMarkerView</classname>
              ,respectively, and custom subclasses of them.</entry>
            </row>

            <row>
              <entry><classname>ContentNegotiatingViewResolver</classname></entry>

              <entry>Implementation of the
              <interfacename>ViewResolver</interfacename> interface that
              resolves a view based on the request file name or
              <literal>Accept</literal> header. See <xref
              linkend="mvc-multiple-representations" />.</entry>
            </row>
          </tbody>
        </tgroup>
      </table>

      <para>As an example, with JSP as a view technology, you can use the
      <classname>UrlBasedViewResolver</classname>. This view resolver
      translates a view name to a URL and hands the request over to the
      RequestDispatcher to render the view.</para>

      <programlisting language="xml">&lt;bean id="viewResolver"
      class="org.springframework.web.servlet.view.UrlBasedViewResolver"&gt;
    &lt;property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/&gt;
    &lt;property name="prefix" value="/WEB-INF/jsp/"/&gt;
    &lt;property name="suffix" value=".jsp"/&gt;
&lt;/bean&gt;</programlisting>

      <para>When returning <literal>test</literal> as a logical view name, this view
      resolver forwards the request to the
      <classname>RequestDispatcher</classname> that will send the request to
      <literal>/WEB-INF/jsp/test.jsp</literal>.</para>

      <para>When you combine different view technologies in a web application,
      you can use the
      <classname>ResourceBundleViewResolver</classname>:</para>

      <programlisting language="xml">&lt;bean id="viewResolver"
      class="org.springframework.web.servlet.view.ResourceBundleViewResolver"&gt;
    &lt;property name="basename" value="views"/&gt;
    &lt;property name="defaultParentView" value="parentView"/&gt;
&lt;/bean&gt;</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. 
      Examples can be found in the next chapter which covers view technologies.
      As you can see, you can identify a parent view, from which all views in
      the properties file <quote>extend</quote>. This
      way you can specify a default view class, for example.</para>

      <note>
        <para>Subclasses of <classname>AbstractCachingViewResolver</classname>
        cache view instances that they resolve. Caching improves performance
        of certain view technologies. It's possible to turn off the cache by
        setting the <literal>cache</literal> property to
        <literal>false</literal>. Furthermore, if you must refresh a certain
        view at runtime (for example when a Velocity template is modified),
        you can use the <literal>removeFromCache(String viewName, Locale
        loc)</literal> method.</para>
      </note>
    </section>

    <section id="mvc-viewresolver-chaining">
      <title>Chaining ViewResolvers</title>

      <para>Spring supports multiple view resolvers. Thus you can chain
      resolvers and, for example, override specific views in certain
      circumstances. You chain view resolvers by adding more than one resolver
      to your application context and, if necessary, by setting the
      <literal>order</literal> property to specify ordering. Remember, the
      higher the order property, the later the view resolver is positioned in
      the chain.</para>

      <para>In the following example, the chain of view resolvers consists of
      two resolvers, an <classname>InternalResourceViewResolver</classname>,
      which is always automatically positioned as the last resolver in the
      chain, and an <classname>XmlViewResolver</classname> for specifying
      Excel views. Excel views are not supported by the
      <classname>InternalResourceViewResolver</classname>.<!--Do you need to say anything else about excel not being supported by one of resolvers? What if anything is the result?--></para>

      <programlisting language="xml">&lt;bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"&gt;
  &lt;property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/&gt;
  &lt;property name="prefix" value="/WEB-INF/jsp/"/&gt;
  &lt;property name="suffix" value=".jsp"/&gt;
&lt;/bean&gt;

&lt;bean id="excelViewResolver" class="org.springframework.web.servlet.view.XmlViewResolver"&gt;
  &lt;property name="order" value="1"/&gt;
  &lt;property name="location" value="/WEB-INF/views.xml"/&gt;
&lt;/bean&gt;

<lineannotation>&lt;!-- in <literal>views.xml</literal> --&gt;</lineannotation>

&lt;beans&gt;
  &lt;bean name="report" class="org.springframework.example.ReportExcelView"/&gt;
&lt;/beans&gt;</programlisting>

      <para>If a specific view resolver does not result in a view, Spring
      examines the context for other view resolvers. If additional view
      resolvers exist, Spring continues to inspect them. <!--So what happens after Spring inspects them?-->If
      they do not exist, Spring throws an <classname>Exception</classname>.</para>

      <para>The contract of a view resolver specifies that a view resolver
      <emphasis>can</emphasis> return null to indicate the view could not be
      found. Not all view resolvers do this, however, because in some cases,
      the resolver simply cannot detect whether or not the view exists. For
      example, the <classname>InternalResourceViewResolver</classname> uses
      the <classname>RequestDispatcher</classname> internally, and dispatching
      is the only way to figure out if a JSP exists, but this action can only
      execute once. The same holds for the
      <classname>VelocityViewResolver</classname> and some others. Check the
      Javadoc for the view resolver to see whether it reports non-existing
      views. Thus, putting an
      <classname>InternalResourceViewResolver</classname> in the chain in a
      place other than the last, results in the chain not being fully
      inspected, because the
      <classname>InternalResourceViewResolver</classname> will
      <emphasis>always</emphasis> return a view!<!--I don't understand the logic of this. How can it return a view if no view exists or no view can be found? this paragraph is confusing.--><!--Why would you put InternalResourceViewResolver in place other than last? It's automatically last. --></para>
    </section>

    <section id="mvc-redirecting">
      <title>Redirecting to views<!--Revise to say what you are redirecting to views. OR are you redirecting views? In that case heading should be Redirecting views.--></title>

      <para>As mentioned previously, a controller typically returns a logical
      view name, which a view resolver resolves to a particular view
      technology. For view technologies such as JSPs that are processed
      through the Servlet or JSP engine, this resolution is usually handled
      through the combination of <classname>InternalResourceViewResolver</classname> and
      <classname>InternalResourceView</classname>, which
      issues an internal forward or include via the Servlet API's
      <literal>RequestDispatcher.forward(..)</literal> method or
      <literal>RequestDispatcher.include()</literal> method. For other view
      technologies, such as Velocity, XSLT, and so on, the view itself
      writes the content directly to 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 that 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 perform a redirect
      before displaying the result is to eliminate the possibility
      of the user submitting the form data multiple times. In this scenario,
      the browser will first send an initial <literal>POST</literal>; it will
      then receive a response to redirect to a different URL; and finally
      the browser will perform a subsequent <literal>GET</literal> for the
      URL named in the redirect response. Thus, from the perspective of the
      browser, the current page does not reflect the result of a
      <literal>POST</literal> but rather of a <literal>GET</literal>. The
      end effect is that there is no way the user can accidentally
      re-<literal>POST</literal> the same data by performing a refresh. The refresh
      forces a <literal>GET</literal> of the result page, not a resend of the
      initial <literal>POST</literal> data.</para>

      <section id="mvc-redirecting-redirect-view">
        <title><classname>RedirectView</classname></title>

        <para>One way to force a redirect as the result of a controller
        response is for the controller to create and return an instance of
        Spring's <classname>RedirectView</classname>. In this case,
        <classname>DispatcherServlet</classname> does not use the normal view
        resolution mechanism. Rather because it has been given the (redirect)
        view already, the <classname>DispatcherServlet</classname> simply
        instructs the view to do its work.</para>

        <para>The <classname>RedirectView</classname> issues an
        <literal>HttpServletResponse.sendRedirect()</literal> call that
        returns to the client browser as an HTTP redirect. <!--Does preceding happen after what happens in first paragraph? Clarify sequence of events.-->All
        model attributes are exposed as HTTP query parameters. This means
        that the model must contain only objects (generally Strings or
        objects converted to a String representation), which can be readily converted to a
        textual HTTP query parameter.</para>

        <para>If you use <classname>RedirectView</classname> and the view is
        created by the controller itself, it is recommended that you configure
        the redirect URL to be injected into the controller so that it is not
        baked into the controller but configured in the context along with the
        view names. <!--I revised sentence because it sounds like something you need to do. Also reworded next heading to say what it's about. If not correct,--><!--reword.-->The
        next section discusses this process.</para>
      </section>

      <section id="mvc-redirecting-redirect-prefix">
        <title>The <literal>redirect:</literal> prefix</title>

        <para>While the use of <classname>RedirectView</classname> works fine,
        if the controller itself creates the
        <classname>RedirectView</classname>, there is no avoiding the
        fact that the controller is aware that a redirection is happening.
        This is really suboptimal and couples things too tightly. The
        controller should not really care about how the response gets
        handled. In general it should operate only in terms of view names that
        have been injected into it.</para>

        <para>The special <literal>redirect:</literal> prefix allows you to
        accomplish this. If a view name is returned that has the prefix
        <literal>redirect:</literal>, the <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
        simply operate in terms of logical view names. A logical view name
        such as <literal>redirect:/my/response/controller.html</literal> will
        redirect relative to the current servlet context, while a name such as
        <literal>redirect:http://myhost.com/some/arbitrary/path.html</literal>
        will redirect to an absolute URL. The important thing is that, as long
        as this redirect view name is injected into the controller like any
        other logical view name, the controller is not even aware that
        redirection is happening.</para>
      </section>

      <section id="mvc-redirecting-forward-prefix">
        <title>The <literal>forward:</literal> prefix<!--Can you revise this heading to say what you're using the forward prefix to accomplish?--></title>

        <para>It is also possible to use a special <literal>forward:</literal>
        prefix for view names that are ultimately resolved by
        <classname>UrlBasedViewResolver</classname> and subclasses. This
        creates an <classname>InternalResourceView</classname> (which
        ultimately does a <literal>RequestDispatcher.forward()</literal>)
        around the rest of the view name, which is considered a URL.
        Therefore, this prefix is not useful with
        <classname>InternalResourceViewResolver</classname> and
        <classname>InternalResourceView</classname> (for JSPs for example).
        But the prefix can be helpful when you are primarily using another
        view technology, but still want to force a forward of a resource to be
        handled by the Servlet/JSP engine. (Note that you may also chain
        multiple view resolvers, instead.)<!--I think the preceding sentences were a bit garbled. I tried to reword a bit. And is this paragraph logical?--></para>

        <para>As with the <literal>redirect:</literal> prefix, if the view
        name with the <literal>forward:</literal> prefix is injected into the controller, the
        controller does not detect that anything special is happening in terms
        of handling the response.<!--Can you reword to clarify the point? The controller does not detect what?--></para>
      </section>
    </section>

    <section id="mvc-multiple-representations">
      <title><classname>ContentNegotiatingViewResolver</classname></title>

      <para>The <classname>ContentNegotiatingViewResolver</classname> does not
      resolve views itself but rather delegates to other view resolvers,
      selecting the view that resembles the representation requested by the
      client. Two strategies exist for a client to request a representation
      from the server:</para>

      <itemizedlist>
        <listitem>
          <para>Use a distinct URI for each resource,
          typically by using a different file extension in the URI. For
          example, the URI<literal>
      http://www.example.com/users/fred.pdf</literal> requests a PDF
          representation of the user fred, and
          <literal>http://www.example.com/users/fred.xml</literal> requests an
          XML representation.</para>
        </listitem>
      </itemizedlist>

      <itemizedlist>
        <listitem>
          <para>Use the same URI for the client to locate the resource, but
          set the <literal>Accept</literal> HTTP request header to list the
          <ulink url="http://en.wikipedia.org/wiki/Internet_media_type">media
          types</ulink> that it understands. For example, an HTTP request for
      <literal>http://www.example.com/users/fred</literal> with an
      <literal>Accept</literal> header set to <literal>application/pdf
      </literal>requests a PDF representation of the user fred, while
      <literal>http://www.example.com/users/fred</literal> with an
      <literal>Accept</literal> header set to <literal>text/xml</literal>
      requests an XML representation. This strategy is known as <ulink
      url="http://en.wikipedia.org/wiki/Content_negotiation">content
      negotiation</ulink>.</para>
        </listitem>
      </itemizedlist>

      <note>
        <para>One issue with the <literal>Accept</literal> header is that it is
        impossible to set it in a web browser within HTML. For example, in Firefox, it is fixed
        to:
        <!--So how would you set the Accept header as in second bullet, if you can't do it in html? Indicate?--></para>

        <programlisting>Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8</programlisting>

        <para>For this reason it is common to see the use of a distinct URI
        for each representation when developing browser based web applications.</para>
      </note>

      <para>To support multiple representations of a resource, Spring provides
      the <classname>ContentNegotiatingViewResolver</classname> to resolve a
      view based on the file extension or <literal>Accept</literal> header of
      the HTTP request. <classname>ContentNegotiatingViewResolver</classname>
      does not perform the view resolution itself but instead delegates to a
      list of view resolvers that you specify through the bean property
      <literal>ViewResolvers</literal>.<!--A human has to specify this list of resolvers, right? See example below.--></para>

      <para>The <classname>ContentNegotiatingViewResolver</classname> selects
      an appropriate <classname>View</classname> to handle the request by
      comparing the request media type(s) with the media type (also known as
      <literal>Content-Type</literal>) supported by the
      <classname>View</classname> associated with each of its
      <classname>ViewResolvers</classname>. The first
      <classname>View</classname> in the list that has a compatible
      <literal>Content-Type</literal> returns the representation to the
      client. If a compatible view cannot be supplied by the 
      <classname>ViewResolver</classname> chain, then the list of views specified 
      through the <literal>DefaultViews</literal> property will be consulted. This 
      latter option is appropriate for singleton <classname>Views</classname> that 
      can render an appropriate representation of the current resource regardless 
      of the logical view name. The <literal>Accept</literal> header may include 
      wildcards, for example text/*, in which case a <classname>View</classname> whose
      Context-Type was text/xml is a compatible match.</para>

      <para>To support the resolution of a view based on a file extension,
      use the <classname>ContentNegotiatingViewResolver </classname>bean
      property <literal>mediaTypes</literal> to specify a mapping of file
      extensions to media types. For more information on the algorithm used 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">&lt;bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver"&gt;
  &lt;property name="mediaTypes"&gt;
    &lt;map&gt;
      &lt;entry key="atom" value="application/atom+xml"/&gt;
      &lt;entry key="html" value="text/html"/&gt;
      &lt;entry key="json" value="application/json"/&gt;
    &lt;/map&gt;
  &lt;/property&gt;
  &lt;property name="viewResolvers"&gt;
    &lt;list&gt;
      &lt;bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/&gt;
      &lt;bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"&gt;
        &lt;property name="prefix" value="/WEB-INF/jsp/"/&gt;
        &lt;property name="suffix" value=".jsp"/&gt;
      &lt;/bean&gt;
    &lt;/list&gt;
  &lt;/property&gt;
  &lt;property name="defaultViews">
    &lt;list>
      &lt;bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView" />
    &lt;/list>
  &lt;/property&gt;
&lt;/bean&gt;


&lt;bean id="content" class="com.springsource.samples.rest.SampleContentAtomView"/&gt;</programlisting>

      <para>The <classname>InternalResourceViewResolver</classname> handles
      the translation of view names and JSP pages, while the
      <classname>BeanNameViewResolver</classname> returns a view based on the
      name of a bean. (See "<link
      linkend="mvc-viewresolver-resolver">Resolving views with the
      ViewResolver interface</link>" for more details on how Spring looks up
      and instantiates a view.) In this example, the
      <literal>content</literal> bean is a class that inherits from
      <classname>AbstractAtomFeedView</classname>, which returns an Atom RSS
      feed. For more information on creating an Atom Feed representation, see
      the section Atom Views.<!--Need a correct link or x-ref re the preceding sentence.I couldn't find an "Atom Views" section.--></para>

      <para>In the above configuration, if a request is made with an <literal>.html</literal>
      extension, the view resolver looks for a view that matches the <literal>text/html</literal>
      media type. The <classname>InternalResourceViewResolver</classname>
      provides the matching view for <literal>text/html</literal>. If the request is made with
      the file extension <literal>.atom</literal>, the view resolver looks for a view that
      matches the <literal>application/atom+xml</literal> media type. This view is provided by
      the <classname>BeanNameViewResolver</classname> that maps to the
      <classname>SampleContentAtomView</classname> if the view name returned
      is <classname>content</classname>. If the request is made with the file extension 
      <literal>.json</literal>, the <classname>MappingJacksonJsonView</classname> instance from 
      the <literal>DefaultViews</literal> list will be selected regardless of the view name. 
      Alternatively, client requests can be made without a file extension but with the 
      <literal>Accept</literal> header set to the preferred media-type, and the same resolution 
      of request to views would occur.<!--Can you reword preceding sentence? I don't follow it.--></para>

      <note>
        <para>If <classname>ContentNegotiatingViewResolver</classname>'s list
        of ViewResolvers is not configured explicitly, it automatically
        uses any ViewResolvers defined in the application context.</para>
      </note>

      <para>The corresponding controller code that returns an Atom RSS feed
      for a URI of the form <literal>http://localhost/content.atom</literal>
      or <literal>http://localhost/content</literal> with an
      <literal>Accept</literal> header of application/atom+xml is shown
      below.</para>

      <programlisting language="java">@Controller
public class ContentController {

    private List&lt;SampleContent&gt; contentList = new ArrayList&lt;SampleContent&gt;();

    @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>In addition to 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, for example, based on a parameter in the request.</para>

    <para>Locale resolvers and interceptors are 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 client (e.g., a web browser). 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 the specified 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">&lt;bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver"&gt;

    &lt;property name="cookieName" value="clientlanguage"/&gt;
    
    <lineannotation>&lt;!-- in seconds. If set to <literal>-1</literal>, the cookie is not persisted (deleted when browser shuts down) --&gt;</lineannotation>
    &lt;property name="cookieMaxAge" value="100000"&gt;

&lt;/bean&gt;</programlisting>

      <table id="mvc-cookie-locale-resolver-props-tbl">
        <title><classname>CookieLocaleResolver</classname> properties</title>

        <tgroup cols="3">
          <colspec colname="c1" colwidth="1*" />

          <colspec colname="c2" colwidth="1*" />

          <colspec colname="c3" colwidth="3*" />

          <thead>
            <row>
              <entry>Property</entry>

              <entry>Default</entry>

              <entry>Description</entry>
            </row>
          </thead>

          <tbody>
            <row>
              <entry>cookieName</entry>

              <entry>classname + LOCALE</entry>

              <entry>The name of the cookie</entry>
            </row>

            <row>
              <entry>cookieMaxAge</entry>

              <entry>Integer.MAX_INT</entry>

              <entry>The maximum time a cookie will stay persistent on the
              client. If -1 is specified, the cookie will not be persisted; it
              will only be available until the client shuts down his or her
              browser.</entry>
            </row>

            <row>
              <entry>cookiePath</entry>

              <entry>/</entry>

              <entry>Limits the visibility of the cookie to a certain part of
              your site. When cookiePath is specified, the cookie will only
              be visible to that path and the paths below it.</entry>
            </row>
          </tbody>
        </tgroup>
      </table>
    </section>

    <section id="mvc-localeresolver-session">
      <title><classname>SessionLocaleResolver</classname></title>

      <para>The <classname>SessionLocaleResolver</classname> allows you to
      retrieve locales from the session that might be associated with the
      user's request.<!--Aren't you missing some information and example? This section has only one sentence.--></para>
    </section>

    <section id="mvc-localeresolver-interceptor">
      <title><classname>LocaleChangeInterceptor</classname></title>

      <para>You can enable changing of locales by adding the
      <classname>LocaleChangeInterceptor</classname> to one of the handler
      mappings (see <xref linkend="mvc-handlermapping" />). It will detect a
      parameter in the request and change the locale. It calls
      <literal>setLocale()</literal> on the
      <interfacename>LocaleResolver</interfacename> that also exists in the
      context. The following example shows that calls to all
      <literal>*.view</literal> resources containing a parameter named
      <literal>siteLanguage</literal> will now change the locale. So, for
      example, a request for the following URL,
      <literal>http://www.sf.net/home.view?siteLanguage=nl</literal> will
      change the site language to Dutch.</para>

      <programlisting language="xml">&lt;bean id="localeChangeInterceptor"
      class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"&gt;
    &lt;property name="paramName" value="siteLanguage"/&gt;
&lt;/bean&gt;

&lt;bean id="localeResolver"
      class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/&gt;

&lt;bean id="urlMapping"
      class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"&gt;
    &lt;property name="interceptors"&gt;
        &lt;list&gt;
            &lt;ref bean="localeChangeInterceptor"/&gt;
        &lt;/list&gt;
    &lt;/property&gt;
    &lt;property name="mappings"&gt;
        &lt;value&gt;/**/*.view=someController&lt;/value&gt;
    &lt;/property&gt;
&lt;/bean&gt;</programlisting>
    </section>
  </section>

  <section id="mvc-themeresolver">
    <title>Using themes</title>

    <section id="mvc-themeresolver-introduction">
      <title>Overview of themes</title>

      <para>You can apply Spring Web MVC framework themes to set the overall look-and-feel
      of your application, thereby enhancing user experience. A theme is a
      collection of static resources, typically style sheets and images, that
      affect the visual style of the application.</para>
    </section>

    <section id="mvc-themeresolver-defining">
      <title>Defining themes</title>

      <para>To use themes in your web application, you must set up an implementation of the 
      <interfacename>org.springframework.ui.context.ThemeSource</interfacename> interface.
      The <interfacename>WebApplicationContext</interfacename> interface extends
      <interfacename>ThemeSource</interfacename> but delegates its
      responsibilities to a dedicated implementation. By default the delegate
      will be an
      <classname>org.springframework.ui.context.support.ResourceBundleThemeSource</classname>
      implementation that loads properties files from the root of the
      classpath. To use a custom <interfacename>ThemeSource</interfacename>
      implementation or to configure the base name prefix of the
      <classname>ResourceBundleThemeSource</classname>, you can register a
      bean in the application context with the reserved name
      <classname>themeSource</classname>. The web application context
      automatically detects a bean with that name and uses it.</para>

      <para>When using the <classname>ResourceBundleThemeSource</classname>, a
      theme is defined in a simple properties file. <!--Revise preceding sentence to clarify: To use ResourceBundleThemeSource, you define a theme in a properties file? OR do you mean a theme--><!--is already defined in a simple properties file for use with ResourceBundleThemeSource?-->The
      properties file lists the resources that make up the theme. Here is an
      example:<!--Is this an example of what a human enters? If not, why is it referred to as an example, if this is exact code already provided?--></para>

      <programlisting>styleSheet=/themes/cool/style.css
background=/themes/cool/img/coolBg.jpg</programlisting>

      <para>The keys of the properties are the names that refer to the themed
      elements from view code. For a JSP, you typically do this using the
      <literal>spring:theme</literal> custom tag, which is very similar to the
      <literal>spring:message</literal> tag. The following JSP fragment uses
      the theme defined in the previous example to customize the look and
      feel:</para>

      <programlisting language="xml">&lt;%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%&gt;
&lt;html&gt;
   &lt;head&gt;
      &lt;link rel="stylesheet" href="&lt;spring:theme code="styleSheet"/&gt;" type="text/css"/&gt;
   &lt;/head&gt;
   &lt;body style="background=&lt;spring:theme code="background"/&gt;"&gt;
      ...
   &lt;/body&gt;
&lt;/html&gt;</programlisting>

      <para>By default, the <classname>ResourceBundleThemeSource</classname>
      uses an empty base name prefix. As a result, the properties files are
      loaded from the root of the classpath. Thus you would put the
      <literal>cool.properties</literal> theme definition in a directory at
      the root of the classpath, for example, in
      <literal>/WEB-INF/classes</literal>. The
      <classname>ResourceBundleThemeSource</classname> uses the standard Java
      resource bundle loading mechanism, allowing for full
      internationalization of themes. For example, we could have a
      <literal>/WEB-INF/classes/cool_nl.properties</literal> that references a
      special background image with Dutch text on it.</para>
    </section>

    <section id="mvc-themeresolver-resolving">
      <title>Theme resolvers</title>

      <para>After you define themes, as in the preceding section, you decide
      which theme to use. The <classname>DispatcherServlet</classname> will
      look for a bean named <classname>themeResolver</classname> to find out
      which <interfacename>ThemeResolver</interfacename> implementation to
      use. A theme resolver works in much the same way as a
      <interfacename>LocaleResolver</interfacename>. It detects the theme to
      use for a particular request and can also alter the request's theme. The
      following theme resolvers are provided by Spring:</para>

      <table id="mvc-theme-resolver-impls-tbl">
        <title><interfacename>ThemeResolver</interfacename>
        implementations</title>

        <tgroup cols="2">
          <colspec colname="c1" colwidth="1*" />

          <colspec colname="c3" colwidth="3*" />

          <thead>
            <row>
              <entry>Class</entry>

              <entry>Description</entry>
            </row>
          </thead>

          <tbody>
            <row>
              <entry><classname>FixedThemeResolver</classname></entry>

              <entry>Selects a fixed theme, set using the
              <classname>defaultThemeName</classname> property.</entry>
            </row>

            <row>
              <entry><classname>SessionThemeResolver</classname></entry>

              <entry>The theme is maintained in the user's HTTP session. It
              only needs to be set once for each session, but is not persisted
              between sessions.</entry>
            </row>

            <row>
              <entry><classname>CookieThemeResolver</classname></entry>

              <entry>The selected theme is stored in a cookie on the client.</entry>
            </row>
          </tbody>
        </tgroup>
      </table>

      <para>Spring also provides a
      <classname>ThemeChangeInterceptor</classname> that allows theme
      changes on every request with a simple request parameter.<!--Do you need more info or an example re preceding sentence?--></para>
    </section>
  </section>

  <section id="mvc-multipart">
    <title>Spring's multipart (fileupload) support</title>

    <section id="mvc-multipart-introduction">
      <title>Introduction</title>

      <para>Spring's built-in multipart support handles file uploads in web
      applications. You enable this multipart support with pluggable
      <interfacename>MultipartResolver</interfacename> objects, defined in the
      <literal>org.springframework.web.multipart</literal> package. <!--I reworded preceding because next paragraph indicates that *you* have to enable; spring does not do multipart handling by default.--><!--Do you mean *you* use pluggable objects to configure mulitpart? Or Spring has accomplished this already?-->Out
      of the box, Spring provides a
      <interfacename>MultipartResolver</interfacename> for use with
      <emphasis>Commons FileUpload</emphasis> (<ulink
      url="http://jakarta.apache.org/commons/fileupload"></ulink>). <!--pdf shows link to apache.org but here it looks blank (although tagged as ulink). Is this link ok?-->How
      uploading files is supported will be described in the rest of this
      chapter.</para>

      <para>By default, Spring does no multipart handling, because some
      developers want to handle multiparts themselves. You enable Spring
      multipart handling by adding a multipart resolver to the web
      application's context. Each request is inspected to see if it contains a
      multipart. If no multipart is found, the request continues as expected.
      If a multipart is found in the request, the
      <classname>MultipartResolver</classname> that has been declared in your
      context is used. After that, the multipart attribute in your request is
      treated like any other attribute.</para>
    </section>

    <section id="mvc-multipart-resolver">
      <title>Using the
      <interfacename>MultipartResolver</interfacename></title>

      <para>The following example shows how to use the
      <classname>CommonsMultipartResolver</classname>:</para>

      <programlisting language="xml">&lt;bean id="multipartResolver"
    class="org.springframework.web.multipart.commons.CommonsMultipartResolver"&gt;

    <lineannotation>&lt;!-- one of the properties available; the maximum file size in bytes --&gt;</lineannotation>
    &lt;property name="maxUploadSize" value="100000"/&gt;
&lt;/bean&gt;</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>.</para>

      <para>When the Spring <classname>DispatcherServlet</classname> detects a
      multi-part request, it activates the resolver that has been declared in
      your context and hands over the request. The resolver then wraps the
      current <classname>HttpServletRequest</classname> into a
      <classname>MultipartHttpServletRequest</classname> that supports
      multipart file uploads. Using the
      <classname>MultipartHttpServletRequest</classname> you can get
      information about the multiparts contained by this request and actually
      get access to the multipart files themselves in your controllers.</para>
    </section>

    <section id="mvc-multipart-forms">
      <title>Handling a file upload in a form</title>

      <para>After the <classname>MultipartResolver</classname> completes its
      job, the request is processed like any other. To use it<!--to use what?-->,
      you create a form with an upload field (see immediately below) that will
      allow the user to upload a form. Then let Spring bind the file onto your
      form (backing object). <!--I reworded because it sounded like you refer twice to creating a form. Where in example do you *let* Spring bind the file? Clarify.--><!--Does reader know what a backing object refers to?--></para>

      <programlisting language="xml">&lt;html&gt;
    &lt;head&gt;
        &lt;title&gt;Upload a file please&lt;/title&gt;
    &lt;/head&gt;
    &lt;body&gt;
        &lt;h1&gt;Please upload a file&lt;/h1&gt;
        &lt;form method="post" action="upload.form" enctype="multipart/form-data"&gt;
            &lt;input type="file" name="file"/&gt;
            &lt;input type="submit"/&gt;
        &lt;/form&gt;
    &lt;/body&gt;
&lt;/html&gt;</programlisting>

      <para>As you can see, we've created a field named after the property of
      the bean that holds the <literal>byte[]</literal>. <!--Preceding sentence: no, byte [] is not shown in preceding example.-->The
      encoding attribute (<literal>enctype="multipart/form-data"</literal>)
      lets the browser know how to encode the multipart fields.</para>

      <para>As with any property that is not automatically <!--changed from *automagically*!-->convertible
      to a string or primitive type, you must register a custom editor with
      the <classname>ServletRequestDatabinder</classname> to be able to put
      binary data in your objects. Two editors can handle files and set the
      results on an object. A <classname>StringMultipartEditor</classname> can
      convert files to Strings (using a user-defined character set), and a
      <classname>ByteArrayMultipartEditor</classname> converts files to byte
      arrays. They function just as the
      <classname>CustomDateEditor</classname> does.</para>

      <para>So, to be able to upload files using an HTML form, declare the
      resolver, a url mapping to a controller that will process the bean, and
      the controller itself:</para>

      <programlisting language="xml">&lt;beans&gt;
  <lineannotation>&lt;!-- lets use the Commons-based implementation of the MultipartResolver interface --&gt;</lineannotation>
    &lt;bean id="multipartResolver"
        class="org.springframework.web.multipart.commons.CommonsMultipartResolver"/&gt;

    &lt;bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"&gt;
        &lt;property name="mappings"&gt;
            &lt;value&gt;
                /upload.form=fileUploadController
            &lt;/value&gt;
        &lt;/property&gt;
    &lt;/bean&gt;

    &lt;bean id="fileUploadController" class="examples.FileUploadController"&gt;
        &lt;property name="commandClass" value="examples.FileUploadBean"/&gt;
        &lt;property name="formView" value="fileuploadform"/&gt;
        &lt;property name="successView" value="confirmation"/&gt;
    &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>After that, create the controller and the actual class to hold the
      file property:<!--Indicate which editor you're using (ByteArray etc.) and what it's doing.--></para>

      <programlisting language="java">public class FileUploadController extends SimpleFormController {

    protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response,
            Object command, BindException errors) throws ServletException, IOException {

        <lineannotation>// cast the bean</lineannotation>
        FileUploadBean bean = (FileUploadBean) command;

        <lineannotation>// let's see if there's content there</lineannotation>
        byte[] file = bean.getFile();
        if (file == null) {
            <lineannotation>// hmm, that's strange, the user did not upload anything</lineannotation>
        }

        <lineannotation>// well, let's do nothing with the bean for now and return</lineannotation>
        return super.onSubmit(request, response, command, errors);
    }

    protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder)
        throws ServletException {
        <lineannotation>// to actually be able to convert Multipart instance to byte[]</lineannotation>
        <lineannotation>// we have to register a custom editor</lineannotation>
        binder.registerCustomEditor(byte[].class, new ByteArrayMultipartFileEditor());
        <lineannotation>// now Spring knows how to handle multipart objects and convert them</lineannotation>
    }
}

public class FileUploadBean {

    private byte[] file;

    public void setFile(byte[] file) {
        this.file = file;
    }

    public byte[] getFile() {
        return file;
    }
}</programlisting>

      <para>As you can see, the <classname>FileUploadBean</classname> has a
      property typed <literal>byte[]</literal> that holds the file. The
      controller registers a custom editor to let Spring know how to convert
      the multipart objects the resolver has found to properties specified by
      the bean. In this example, nothing is done with the
      <literal>byte[]</literal> property of the bean itself, but in practice
      you can do save it in a database, mail it to somebody, and so on.</para>

      <para>The following is an equivalent example in which a file is bound
      straight to a String-typed property on a (form backing) object:<!--mention editor and its role.--></para>

      <programlisting language="java">public class FileUploadController extends SimpleFormController {

    protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response,
            Object command, BindException errors) throws ServletException, IOException {

        <lineannotation>// cast the bean</lineannotation>
        FileUploadBean bean = (FileUploadBean) command;

        <lineannotation>// let's see if there's content there</lineannotation>
        String file = bean.getFile();
        if (file == null) {
            <lineannotation>// hmm, that's strange, the user did not upload anything</lineannotation>
        }

        <lineannotation>// well, let's do nothing with the bean for now and return</lineannotation>
        return super.onSubmit(request, response, command, errors);
    }

    protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder)
        throws ServletException {
        // to actually be able to convert Multipart instance to a String
        // we have to register a custom editor
        binder.registerCustomEditor(String.class, new StringMultipartFileEditor());
        // now Spring knows how to handle multipart object and convert them
    }

}

public class FileUploadBean {

    private String file;

    public void setFile(String file) {
        this.file = file;
    }

    public String getFile() {
        return file;
    }
}</programlisting>

      <para>The preceding example only makes (logical) sense in the context of
      uploading a plain text file. It would not work as well with an image
      file upload.</para>

      <para>The third (and final) option is where one binds directly to a
      <interfacename>MultipartFile</interfacename> property declared on the
      (form backing) object's class. In this case one does not need to
      register any custom <interfacename>PropertyEditor</interfacename>
      because there is no type conversion to be performed.</para>

      <programlisting language="java">public class FileUploadController extends SimpleFormController {

    protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response,
            Object command, BindException errors) throws ServletException, IOException {

        <lineannotation>// cast the bean</lineannotation>
        FileUploadBean bean = (FileUploadBean) command;

        <lineannotation> let's see if there's content there</lineannotation>
        MultipartFile file = bean.getFile();
        if (file == null) {
            <lineannotation>// hmm, that's strange, the user did not upload anything</lineannotation>
        }

        <lineannotation>// well, let's do nothing with the bean for now and return</lineannotation>
        return super.onSubmit(request, response, command, errors);
    }
}

public class FileUploadBean {

    private MultipartFile file;

    public void setFile(MultipartFile file) {
        this.file = file;
    }

    public MultipartFile getFile() {
        return file;
    }
}</programlisting>
    </section>
  </section>

  <section id="mvc-exceptionhandlers">
    <title>Handling exceptions</title>

    <section>
      <title
      id="mvc-HandlerExceptionResolver"><interfacename>HandlerExceptionResolver<!--I thought HandlerExceptionResolver needed its own section.--></interfacename></title>

      <para>Spring <literal>HandlerExceptionResolvers</literal> ease the pain
      of unexpected exceptions that occur while your request is handled by a
      controller that matched the request.
    <literal>HandlerExceptionResolvers</literal> somewhat resemble the
    exception mappings you can define in the web application descriptor
    <literal>web.xml</literal>. However, they provide a more flexible way to
      handle exceptions. They provide information about which handler was
    executing when the exception was thrown. Furthermore, a programmatic way
      of handling exception gives you more options for responding
      appropriately before the request is forwarded to another URL (the same
      end result as when you use the servlet specific exception
      mappings).</para>

    <para>Besides implementing the
    <interfacename>HandlerExceptionResolver</interfacename> interface, which
      is only a matter of implementing the
      <literal>resolveException(Exception, Handler)</literal> method and
      returning a <classname>ModelAndView</classname>, you may also use the
    <classname>SimpleMappingExceptionResolver</classname>. This resolver
    enables you to take the class name of any exception that might be thrown
    and map it to a view name. This is functionally equivalent to the
      exception mapping feature from the Servlet API, but it is also possible
      to implement more finely grained mappings of exceptions from different
    handlers.</para>
    </section>

    <section id="mvc-ann-exceptionhandler">
      <title><interfacename>@ExceptionHandler<!--Changed this from @ExceptionResolver because text and example say @ExceptionHandler.--></interfacename></title>

      <para>An alternative to the
      <interfacename>HandlerExceptionResolver</interfacename> interface is the
      <interfacename>@ExceptionHandler</interfacename> annotation. You use the
      <classname>@ExceptionHandler</classname> method annotation within a
      controller to specify which method is invoked when an exception of a
      specific type is thrown during the execution of controller methods. For
      example:</para>

      <programlisting language="java">@Controller
public class SimpleController {

  // other controller method omitted

  @ExceptionHandler(IOException.class)
  public String handleIOException(IOException ex, HttpServletRequest request) {
    return ClassUtils.getShortName(ex.getClass());
  }
}</programlisting>

      <para>will invoke the 'handlerIOException' method when a
      <classname>java.io.IOException</classname> is thrown.</para>

      <para>The <classname>@ExceptionHandler</classname> value can be set to
      an array of Exception types. If an exception is thrown matches one of
      the types in the list, then the method annotated with the matching
      <classname>@ExceptionHandler</classname> will be invoked. If the
      annotation value is not set then the exception types listed as method
      arguments are used.</para>

      <para>Much like standard controller methods annotated with a
      <classname>@RequestMapping</classname> annotation, the method arguments
      and return values of <classname>@ExceptionHandler</classname> methods
      are very flexible. For example, the
      <classname>HttpServletRequest</classname> can be accessed in Servlet
      environments and the <classname>PortletRequest</classname> in Portlet
      environments. The return type can be a <classname>String</classname>,
      which is interpreted as a view name or a
      <classname>ModelAndView</classname> object. Refer to the API
      documentation for more details.</para>
    </section>
  </section>

  <section id="mvc-coc">
    <title>Convention over configuration support</title>

    <para>For a lot of projects, sticking to established conventions and
    having reasonable defaults is just what they (the projects) need... this
    theme of convention-over-configuration now has explicit support in Spring
    Web MVC. What this means is that if you establish a set of naming
    conventions and suchlike, you can <emphasis>substantially</emphasis> cut
    down on the amount of configuration that is required to set up handler
    mappings, view resolvers, <classname>ModelAndView</classname> instances,
    etc. This is a great boon with regards to rapid prototyping, and can also
    lend a degree of (always good-to-have) consistency across a codebase
    should you choose to move forward with it into production.</para>

    <para>Convention-over-configuration support addresses the three core areas
    of MVC -- models, views, and controllers.</para>

    <section id="mvc-coc-ccnhm">
      <title>The Controller
      <classname>ControllerClassNameHandlerMapping</classname></title>

      <para>The <classname>ControllerClassNameHandlerMapping</classname> class
      is a <interfacename>HandlerMapping</interfacename> implementation that
      uses a convention to determine the mapping between request URLs and the
      <interfacename>Controller</interfacename> instances that are to handle
      those requests.</para>

      <para>Consider the following simple
      <interfacename>Controller</interfacename> implementation. Take special
      notice of the <emphasis>name</emphasis> of the class.<!--Re preceding sentence, I don't see where the name of the class is discussed in explanation following the example. See my next comment.--></para>

      <programlisting language="java">public class <emphasis role="bold">ViewShoppingCartController</emphasis> implements Controller {

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
        <lineannotation>// the implementation is not hugely important for this example...</lineannotation>
    }
}</programlisting>

      <para>Here is a snippet from the attendent Spring Web MVC configuration
      file...</para>

      <programlisting language="xml">&lt;bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/&gt;
                
&lt;bean id="<emphasis role="bold">viewShoppingCart</emphasis>" class="x.y.z.ViewShoppingCartController"&gt;
    <lineannotation>&lt;!-- inject dependencies as required... --&gt;</lineannotation>
&lt;/bean&gt;</programlisting>

      <para>The <classname>ControllerClassNameHandlerMapping</classname> finds
      all of the various handler (or
      <interfacename>Controller</interfacename>) beans defined in its
      application context and strips <literal>Controller</literal> off the
      name to define its handler mappings. Thus,
      <classname>ViewShoppingCartController</classname> maps to the
      <literal>/viewshoppingcart*</literal> request URL.</para>

      <para>Let's look at some more examples so that the central idea becomes
      immediately familiar. (Notice all lowercase in the URLs, in contrast to
      camel-cased <interfacename>Controller</interfacename> class
      names.)</para>

      <itemizedlist>
        <listitem>
          <para><classname>WelcomeController</classname> maps to the
          <literal>/welcome*</literal> request URL</para>
        </listitem>

        <listitem>
          <para><classname>HomeController</classname> maps to the
          <literal>/home*</literal> request URL</para>
        </listitem>

        <listitem>
          <para><classname>IndexController</classname> maps to the
          <literal>/index*</literal> request URL</para>
        </listitem>

        <listitem>
          <para><classname>RegisterController</classname> maps to the
          <literal>/register*</literal> request URL</para>
        </listitem>
      </itemizedlist>

      <para>In the case of <classname>MultiActionController</classname>
      handler classes, the mappings generated are slightly more complex. The
      <interfacename>Controller</interfacename> names in the following
      examples are assumed to be <classname>MultiActionController</classname>
      implementations:</para>

      <itemizedlist>
        <listitem>
          <para><classname>AdminController</classname> maps to the
          <literal>/admin</literal><emphasis role="bold">/*</emphasis> request
          URL</para>
        </listitem>

        <listitem>
          <para><classname>CatalogController</classname> maps to the
          <literal>/catalog</literal><emphasis role="bold">/*</emphasis>
          request URL</para>
        </listitem>
      </itemizedlist>

      <para>If you follow the convention of naming your
      <interfacename>Controller</interfacename> implementations as
      <literal>xxx</literal><emphasis role="bold">Controller</emphasis>, the
      <classname>ControllerClassNameHandlerMapping</classname> saves you the
      tedium of defining and maintaining a potentially
      <emphasis>looooong</emphasis>
      <classname>SimpleUrlHandlerMapping</classname> (or suchlike).</para>

      <para>The <classname>ControllerClassNameHandlerMapping</classname> class
      extends the <classname>AbstractHandlerMapping</classname> base class so
      you can define <interfacename>HandlerInterceptor</interfacename>
      instances and everything else just as you would with many other
      <interfacename>HandlerMapping</interfacename> implementations.</para>
    </section>

    <section id="mvc-coc-modelmap">
      <title>The Model <classname>ModelMap</classname>
      (<classname>ModelAndView</classname>)</title>

      <para>The <classname>ModelMap</classname> class is essentially a
      glorified <interfacename>Map</interfacename> that can make adding
      objects that are to be displayed in (or on) a
      <interfacename>View</interfacename> adhere to a common naming
      convention. Consider the following
      <interfacename>Controller</interfacename> implementation; notice that
      objects are added to the <classname>ModelAndView</classname> without any
      associated name specified.</para>

      <programlisting language="java">public class DisplayShoppingCartController implements Controller {

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
        
        List cartItems = <lineannotation>// get a <interfacename>List</interfacename> of <classname>CartItem</classname> objects</lineannotation>
        User user = <lineannotation>// get the <classname>User</classname> doing the shopping</lineannotation>
        
        ModelAndView mav = new ModelAndView("displayShoppingCart"); <lineannotation>&lt;-- the logical view name</lineannotation>

        mav.addObject(cartItems); <lineannotation>&lt;-- look ma, no name, just the object</lineannotation>
        mav.addObject(user); <lineannotation>&lt;-- and again ma!</lineannotation>

        return mav;
    }
}</programlisting>

      <para>The <classname>ModelAndView</classname> class uses a
      <classname>ModelMap</classname> class that is a custom
      <interfacename>Map</interfacename> implementation that automatically
      generates a key for an object when an object is added to it. The
      strategy for determining the name for an added object is, in the case of
      a scalar object such as <classname>User</classname>, to use the short
      class name of the object's class. The following examples are names that
      are generated for scalar objects put into a
      <classname>ModelMap</classname> instance.</para>

      <itemizedlist>
        <listitem>
          <para>An <classname>x.y.User</classname> instance added will have
          the name <literal>user</literal> generated.</para>
        </listitem>

        <listitem>
          <para>An <classname>x.y.Registration</classname> instance added will
          have the name <literal>registration</literal> generated.</para>
        </listitem>

        <listitem>
          <para>An <classname>x.y.Foo</classname> instance added will have the
          name <literal>foo</literal> generated.</para>
        </listitem>

        <listitem>
          <para>A <classname>java.util.HashMap</classname> instance added will
          have the name <literal>hashMap</literal> generated. You probably
          want to be explicit about the name in this case because
          <literal>hashMap</literal> is less than intuitive.</para>
        </listitem>

        <listitem>
          <para>Adding <literal>null</literal> will result in an
          <classname>IllegalArgumentException</classname> being thrown. If the
          object (or objects) that you are adding could be
          <literal>null</literal>, then you will also want to be explicit
          about the name.</para>
        </listitem>
      </itemizedlist>

      <sidebar>
        <title>What, no automatic pluralisation?</title>

        <para>Spring Web MVC's convention-over-configuration support does not
        support automatic pluralisation. That is, you cannot add a
        <interfacename>List</interfacename> of <classname>Person</classname>
        objects to a <classname>ModelAndView</classname> and have the
        generated name be <classname>people</classname>.</para>

        <para>This decision was made after some debate, with the
        <quote>Principle of Least Surprise</quote> winning out in the
        end.</para>
      </sidebar>

      <para>The strategy for generating a name after adding a
      <interfacename>Set</interfacename>, <interfacename>List</interfacename>
      or array object is to peek into the collection, take the short class
      name of the first object in the collection, and use that with
      <literal>List</literal> appended to the name. Some examples will make
      the semantics of name generation for collections clearer...</para>

      <itemizedlist>
        <listitem>
          <para>An <classname>x.y.User[]</classname> array with one or more
          <classname>x.y.User</classname> elements added will have the name
          <literal>userList</literal> generated.</para>
        </listitem>

        <listitem>
          <para>An <classname>x.y.Foo[]</classname> array with one or more
          <classname>x.y.User</classname> elements added will have the name
          <literal>fooList</literal> generated.</para>
        </listitem>

        <listitem>
          <para>A <classname>java.util.ArrayList</classname> with one or more
          <classname>x.y.User</classname> elements added will have the name
          <literal>userList</literal> generated.</para>
        </listitem>

        <listitem>
          <para>A <classname>java.util.HashSet</classname> with one or more
          <classname>x.y.Foo</classname> elements added will have the name
          <literal>fooList</literal> generated.</para>
        </listitem>

        <listitem>
          <para>An <emphasis role="bold">empty</emphasis>
          <classname>java.util.ArrayList</classname> will not be added at all
          (in effect, the <methodname>addObject(..)</methodname> call will
          essentially be a no-op).</para>
        </listitem>
      </itemizedlist>
    </section>

    <section id="mvc-coc-r2vnt">
      <title>The View -
      <interfacename>RequestToViewNameTranslator</interfacename></title>

      <para>The <interfacename>RequestToViewNameTranslator</interfacename>
      interface determines a logical <interfacename>View</interfacename> name
      when no such logical view name is explicitly supplied. It has just one
      implementation, the
      <classname>DefaultRequestToViewNameTranslator</classname> class.</para>

      <para>The <classname>DefaultRequestToViewNameTranslator</classname> maps
      request URLs to logical view names, as with this example:</para>

      <programlisting language="java">public class RegistrationController implements Controller {
                
    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
        <lineannotation>// process the request...</lineannotation>
        ModelAndView mav = new ModelAndView();
        <lineannotation>// add <emphasis role="bold">data</emphasis> as necessary to the model...</lineannotation>
        return mav;
        <lineannotation>// notice that no <interfacename>View</interfacename> or logical view name has been set</lineannotation>
    }
}</programlisting>

      <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN"
        "http://www.springframework.org/dtd/spring-beans-2.0.dtd"&gt;
&lt;beans&gt;

    <lineannotation>&lt;!-- this bean with the well known name generates view names for us --&gt;</lineannotation>
    &lt;bean id="viewNameTranslator" class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/&gt;

    &lt;bean class="x.y.RegistrationController"&gt;
        <lineannotation>&lt;!-- inject dependencies as necessary --&gt;</lineannotation>
    &lt;/bean&gt;
    
    <lineannotation>&lt;!-- maps request URLs to Controller names --&gt;</lineannotation>
    &lt;bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/&gt;

    &lt;bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"&gt;
        &lt;property name="prefix" value="/WEB-INF/jsp/"/&gt;
        &lt;property name="suffix" value=".jsp"/&gt;
    &lt;/bean&gt;

&lt;/beans&gt;
</programlisting>

      <para>Notice how in the implementation of the
      <literal>handleRequest(..)</literal> method no
      <interfacename>View</interfacename> or logical view name is ever set on
      the <classname>ModelAndView</classname> that is returned. The
      <classname>DefaultRequestToViewNameTranslator</classname> is tasked with
      generating a <emphasis>logical view name</emphasis> from the URL of the
      request. In the case of the above
      <classname>RegistrationController</classname>, which is used in
      conjunction with the
      <classname>ControllerClassNameHandlerMapping</classname>, a request URL
      of <literal>http://localhost/registration.html</literal> results in a
      logical view name of <literal>registration</literal> being generated by
      the <classname>DefaultRequestToViewNameTranslator</classname>. This
      logical view name is then resolved into the
      <literal>/WEB-INF/jsp/registration.jsp</literal> view by the
      <classname>InternalResourceViewResolver</classname> bean.</para>

      <tip>
        <para>You do not need to define a
        <classname>DefaultRequestToViewNameTranslator</classname> bean
        explicitly. If you like the default settings of the
        <classname>DefaultRequestToViewNameTranslator</classname>, you can
        rely on the Spring Web MVC <classname>DispatcherServlet</classname> to
        instantiate an instance of this class if one is not explicitly
        configured.</para>
      </tip>

      <para>Of course, if you need to change the default settings, then you do
      need to configure your own
      <classname>DefaultRequestToViewNameTranslator</classname> bean
      explicitly. Consult the comprehensive Javadoc for the
      <classname>DefaultRequestToViewNameTranslator</classname> class for
      details of the various properties that can be configured.</para>
    </section>
  </section>

  <section id="mvc-etag">
    <title>ETag support</title>

    <para>An <ulink url="http://en.wikipedia.org/wiki/HTTP_ETag">ETag</ulink>
    (entity tag) is an HTTP response header returned by an HTTP/1.1 compliant
    web server used to determine change in content at a given URL. It can be
    considered to be the more sophisticated successor to the
    <literal>Last-Modified</literal> header. When a server returns a
    representation with an ETag header, the client can use this header in
    subsequent GETs, in an <literal>If-None-Match</literal> header. If the
    content has not changed, the server returns <literal>304: Not
    Modified</literal>.</para>

    <para>Support for ETags is provided by the servlet filter
    <classname>ShallowEtagHeaderFilter</classname>. It is a plain Servlet
    Filter, and thus can be used in combination with any web framework. <!--The preceding sentence was a fragment, not a complete sentence. Have I reworded ok?-->The
    <classname>ShallowEtagHeaderFilter</classname> filter creates so-called
    shallow ETags (as opposed to deep ETags, more about that later).<!--Provide xref to deep ETags.-->The
    filter caches the content of the rendered JSP (or other content),
    generates an MD5 hash over that, and returns that as an ETag header in the
    response. The next time a client sends a request for the same resource, it
    uses that hash as the <literal>If-None-Match</literal> value. The filter
    detects this, renders the view again, and compares the two hashes. If they
    are equal, a <literal>304</literal> is returned. This filter will not save
    processing power, as the view is still rendered. The only thing it saves
    is bandwidth, as the rendered response is not sent back over the
    wire.</para>

    <para>You configure the <classname>ShallowEtagHeaderFilter</classname> in
    <filename>web.xml</filename>:</para>

    <programlisting language="xml">&lt;filter&gt;
  &lt;filter-name&gt;etagFilter&lt;/filter-name&gt;
    &lt;filter-class&gt;org.springframework.web.filter.ShallowEtagHeaderFilter&lt;/filter-class&gt;
&lt;/filter&gt;

&lt;filter-mapping&gt;
  &lt;filter-name&gt;etagFilter&lt;/filter-name&gt;
  &lt;servlet-name&gt;petclinic&lt;/servlet-name&gt;
&lt;/filter-mapping&gt;</programlisting>
  </section>

  <section id="mvc-resources">
    <title>More Spring Web MVC Resources</title>

    <para>See the following links and pointers for more resources about Spring
    Web MVC:</para>

    <itemizedlist>
      <listitem>
        <para>The Spring distribution ships with a Spring Web MVC tutorial
        that guides the reader through building a complete Spring Web
        MVC-based application using a step-by-step approach. This tutorial is
        available in the <literal>docs</literal> directory of the Spring
        distribution. An online version can also be found on the <ulink
        url="http://springframework.org/">Spring Framework
        website</ulink>.</para>
      </listitem>

      <listitem>
        <para><quote>Expert Spring Web MVC and Web Flow</quote> by Seth Ladd
        and others (published by Apress) is an excellent hard copy source of
        Spring Web MVC goodness.</para>
      </listitem>
    </itemizedlist>
  </section>
</chapter>