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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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<chapter id="view">
  <title>View technologies</title>

  <section id="view-introduction">
    <title>Introduction</title>

    <para>One of the areas in which Spring excels is in the separation of view
    technologies from the rest of the MVC framework. For example, deciding to
    use Velocity or XSLT in place of an existing JSP is primarily a matter of
    configuration. This chapter covers the major view technologies that work
    with Spring and touches briefly on how to add new ones. This chapter
    assumes you are already familiar with <xref linkend="mvc-viewresolver" />
    which covers the basics of how views in general are coupled to the MVC
    framework.</para>
  </section>

  <section id="view-jsp">
    <title>JSP &amp; JSTL</title>

    <para>Spring provides a couple of out-of-the-box solutions for JSP and
    JSTL views. Using JSP or JSTL is done using a normal view resolver defined
    in the <interfacename>WebApplicationContext</interfacename>. Furthermore,
    of course you need to write some JSPs that will actually render the
    view.</para>

    <section id="view-jsp-resolver">
      <title>View resolvers</title>

      <para>Just as with any other view technology you're integrating with
      Spring, for JSPs you'll need a view resolver that will resolve your
      views. The most commonly used view resolvers when developing with JSPs
      are the <classname>InternalResourceViewResolver</classname> and the
      <classname>ResourceBundleViewResolver</classname>. Both are declared in
      the <interfacename>WebApplicationContext</interfacename>:</para>

      <programlisting language="xml"><lineannotation>&lt;!-- the <classname>ResourceBundleViewResolver</classname> --&gt;</lineannotation>
&lt;bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"&gt;
  &lt;property name="basename" value="views"/&gt;
&lt;/bean&gt;

<lineannotation># And a sample properties file is uses (views.properties in WEB-INF/classes):</lineannotation>
welcome.class=org.springframework.web.servlet.view.JstlView
welcome.url=/WEB-INF/jsp/welcome.jsp

productList.class=org.springframework.web.servlet.view.JstlView
productList.url=/WEB-INF/jsp/productlist.jsp</programlisting>

      <para>As you can see, the
      <classname>ResourceBundleViewResolver</classname> needs a properties
      file defining the view names mapped to 1) a class and 2) a URL. With a
      <classname>ResourceBundleViewResolver</classname> you can mix different
      types of views using only one resolver.</para>

      <programlisting language="xml">&lt;bean id="viewResolver" 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;</programlisting>

      <para>The <classname>InternalResourceBundleViewResolver</classname> can
      be configured for using JSPs as described above. As a best practice, we
      strongly encourage placing your JSP files in a directory under the
      <filename class="directory">'WEB-INF'</filename> directory, so there can
      be no direct access by clients.</para>
    </section>

    <section id="view-jsp-jstl">
      <title>'Plain-old' JSPs versus JSTL</title>

      <para>When using the Java Standard Tag Library you must use a special
      view class, the <classname>JstlView</classname>, as JSTL needs some
      preparation before things such as the i18N features will work.</para>
    </section>

    <section id="view-jsp-tags">
      <title>Additional tags facilitating development</title>

      <para>Spring provides data binding of request parameters to command
      objects as described in earlier chapters. To facilitate the development
      of JSP pages in combination with those data binding features, Spring
      provides a few tags that make things even easier. All Spring tags have
      <emphasis>HTML escaping</emphasis> features to enable or disable
      escaping of characters.</para>

      <para>The tag library descriptor (TLD) is included in the <filename
      class="libraryfile">spring.jar</filename> as well in the distribution
      itself. Further information about the individual tags can be found in
      the appendix entitled <xref linkend="spring.tld" />.</para>
    </section>

    <section id="view-jsp-formtaglib">
      <title>Using Spring's form tag library</title>

      <para>As of version 2.0, Spring provides a comprehensive set of data
      binding-aware tags for handling form elements when using JSP and Spring
      Web MVC. Each tag provides support for the set of attributes of its
      corresponding HTML tag counterpart, making the tags familiar and
      intuitive to use. The tag-generated HTML is HTML 4.01/XHTML 1.0
      compliant.</para>

      <para>Unlike other form/input tag libraries, Spring's form tag library
      is integrated with Spring Web MVC, giving the tags access to the command
      object and reference data your controller deals with. As you will see in
      the following examples, the form tags make JSPs easier to develop, read
      and maintain.</para>

      <para>Let's go through the form tags and look at an example of how each
      tag is used. We have included generated HTML snippets where certain tags
      require further commentary.</para>

      <section id="view-jsp-formtaglib-configuration">
        <title>Configuration</title>

        <para>The form tag library comes bundled in
        <literal>spring.jar</literal>. The library descriptor is called
        <literal>spring-form.tld</literal>.</para>

        <para>To use the tags from this library, add the following directive
        to the top of your JSP page:</para>

        <programlisting language="xml">&lt;%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %&gt;</programlisting>

        <para>... where <literal>form</literal> is the tag name prefix you
        want to use for the tags from this library.</para>
      </section>

      <section id="view-jsp-formtaglib-formtag">
        <title>The <literal>form</literal> tag</title>

        <para>This tag renders an HTML 'form' tag and exposes a binding path
        to inner tags for binding. It puts the command object in the
        <literal>PageContext</literal> so that the command object can be
        accessed by inner tags. <emphasis>All the other tags in this library
        are nested tags of the <literal>form</literal> tag</emphasis>.</para>

        <para>Let's assume we have a domain object called
        <classname>User</classname>. It is a JavaBean with properties such as
        <literal>firstName</literal> and <literal>lastName</literal>. We will
        use it as the form backing object of our form controller which returns
        <literal>form.jsp</literal>. Below is an example of what
        <literal>form.jsp</literal> would look like:</para>

        <programlisting language="xml">&lt;form:form&gt;
      &lt;table&gt;
          &lt;tr&gt;
              &lt;td&gt;First Name:&lt;/td&gt;
              &lt;td&gt;&lt;form:input path="firstName" /&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td&gt;Last Name:&lt;/td&gt;
              &lt;td&gt;&lt;form:input path="lastName" /&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td colspan="2"&gt;
                  &lt;input type="submit" value="Save Changes" /&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
      &lt;/table&gt;
  &lt;/form:form&gt;</programlisting>

        <para>The <literal>firstName</literal> and <literal>lastName</literal>
        values are retrieved from the command object placed in the
        <interfacename>PageContext</interfacename> by the page controller.
        Keep reading to see more complex examples of how inner tags are used
        with the <literal>form</literal> tag.</para>

        <para>The generated HTML looks like a standard form:</para>

        <programlisting language="xml">&lt;form method="POST"&gt;
      &lt;table&gt;
        &lt;tr&gt;
            &lt;td&gt;First Name:&lt;/td&gt;
            &lt;td&gt;&lt;input name="firstName" type="text" value="Harry"/&gt;&lt;/td&gt;
        &lt;/tr&gt;
        &lt;tr&gt;
            &lt;td&gt;Last Name:&lt;/td&gt;
            &lt;td&gt;&lt;input name="lastName" type="text" value="Potter"/&gt;&lt;/td&gt;
        &lt;/tr&gt;
        &lt;tr&gt;
            &lt;td colspan="2"&gt;
              &lt;input type="submit" value="Save Changes" /&gt;
            &lt;/td&gt;
        &lt;/tr&gt;
      &lt;/table&gt;
  &lt;/form&gt;</programlisting>

        <para>The preceding JSP assumes that the variable name of the form
        backing object is <literal>'command'</literal>. If you have put the
        form backing object into the model under another name (definitely a
        best practice), then you can bind the form to the named variable like
        so:</para>

        <programlisting language="xml">&lt;form:form <lineannotation><emphasis
              role="bold">commandName="user"</emphasis></lineannotation>&gt;
      &lt;table&gt;
          &lt;tr&gt;
              &lt;td&gt;First Name:&lt;/td&gt;
              &lt;td&gt;&lt;form:input path="firstName" /&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td&gt;Last Name:&lt;/td&gt;
              &lt;td&gt;&lt;form:input path="lastName" /&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td colspan="2"&gt;
                  &lt;input type="submit" value="Save Changes" /&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
      &lt;/table&gt;
  &lt;/form:form&gt;</programlisting>
      </section>

      <section id="view-jsp-formtaglib-inputtag">
        <title>The <literal>input</literal> tag</title>

        <para>This tag renders an HTML 'input' tag with type 'text' using the
        bound value. For an example of this tag, see <xref
        linkend="view-jsp-formtaglib-formtag" />.</para>
      </section>

      <section id="view-jsp-formtaglib-checkboxtag">
        <title>The <literal>checkbox</literal> tag</title>

        <para>This tag renders an HTML 'input' tag with type
        'checkbox'.</para>

        <para>Let's assume our <classname>User</classname> has preferences
        such as newsletter subscription and a list of hobbies. Below is an
        example of the <classname>Preferences</classname> class:</para>
      </section>

      <programlisting language="java">public class Preferences {

      private boolean receiveNewsletter;

      private String[] interests;

      private String favouriteWord;

      public boolean isReceiveNewsletter() {
          return receiveNewsletter;
      }

      public void setReceiveNewsletter(boolean receiveNewsletter) {
          this.receiveNewsletter = receiveNewsletter;
      }

      public String[] getInterests() {
          return interests;
      }

      public void setInterests(String[] interests) {
          this.interests = interests;
      }

      public String getFavouriteWord() {
          return favouriteWord;
      }

      public void setFavouriteWord(String favouriteWord) {
          this.favouriteWord = favouriteWord;
      }
  }</programlisting>

      <para>The <literal>form.jsp</literal> would look like:</para>

      <programlisting language="xml">&lt;form:form&gt;
      &lt;table&gt;
          &lt;tr&gt;
              &lt;td&gt;Subscribe to newsletter?:&lt;/td&gt;
              <lineannotation>&lt;%-- Approach 1: Property is of type <classname>java.lang.Boolean</classname> --%&gt;</lineannotation>
              &lt;td&gt;&lt;form:checkbox path="preferences.receiveNewsletter"/&gt;&lt;/td&gt;
          &lt;/tr&gt;

          &lt;tr&gt;
              &lt;td&gt;Interests:&lt;/td&gt;
              &lt;td&gt;
                  <lineannotation>&lt;%-- Approach 2: Property is of an array or of type <interfacename>java.util.Collection</interfacename> --%&gt;</lineannotation>
                  Quidditch: &lt;form:checkbox path="preferences.interests" value="Quidditch"/&gt;
                  Herbology: &lt;form:checkbox path="preferences.interests" value="Herbology"/&gt;
                  Defence Against the Dark Arts: &lt;form:checkbox path="preferences.interests"
                      value="Defence Against the Dark Arts"/&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td&gt;Favourite Word:&lt;/td&gt;
              &lt;td&gt;
                  <lineannotation>&lt;%-- Approach 3: Property is of type <classname>java.lang.Object</classname> --%&gt;</lineannotation>
                  Magic: &lt;form:checkbox path="preferences.favouriteWord" value="Magic"/&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
      &lt;/table&gt;
  &lt;/form:form&gt;</programlisting>

      <para>There are 3 approaches to the <literal>checkbox</literal> tag
      which should meet all your checkbox needs. <itemizedlist>
          <listitem>
            <para>Approach One - When the bound value is of type
            <literal>java.lang.Boolean</literal>, the
            <literal>input(checkbox)</literal> is marked as 'checked' if the
            bound value is <literal>true</literal>. The
            <literal>value</literal> attribute corresponds to the resolved
            value of the <literal>setValue(Object)</literal> value
            property.</para>
          </listitem>

          <listitem>
            <para>Approach Two - When the bound value is of type
            <literal>array</literal> or
            <interfacename>java.util.Collection</interfacename>, the
            <literal>input(checkbox)</literal> is marked as 'checked' if the
            configured <literal>setValue(Object)</literal> value is present in
            the bound <interfacename>Collection</interfacename>.</para>
          </listitem>

          <listitem>
            <para>Approach Three - For any other bound value type, the
            <literal>input(checkbox)</literal> is marked as 'checked' if the
            configured <literal>setValue(Object)</literal> is equal to the
            bound value.</para>
          </listitem>
        </itemizedlist></para>

      <para>Note that regardless of the approach, the same HTML structure is
      generated. Below is an HTML snippet of some checkboxes:</para>

      <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Interests:&lt;/td&gt;
      &lt;td&gt;
          Quidditch: &lt;input name="preferences.interests" type="checkbox" value="Quidditch"/&gt;
          &lt;input type="hidden" value="1" name="_preferences.interests"/&gt;
          Herbology: &lt;input name="preferences.interests" type="checkbox" value="Herbology"/&gt;
          &lt;input type="hidden" value="1" name="_preferences.interests"/&gt;
          Defence Against the Dark Arts: &lt;input name="preferences.interests" type="checkbox"
              value="Defence Against the Dark Arts"/&gt;
          &lt;input type="hidden" value="1" name="_preferences.interests"/&gt;
      &lt;/td&gt;
  &lt;/tr&gt;</programlisting>

      <para>What you might not expect to see is the additional hidden field
      after each checkbox. When a checkbox in an HTML page is
      <emphasis>not</emphasis> checked, its value will not be sent to the
      server as part of the HTTP request parameters once the form is
      submitted, so we need a workaround for this quirk in HTML in order for
      Spring form data binding to work. The <literal>checkbox</literal> tag
      follows the existing Spring convention of including a hidden parameter
      prefixed by an underscore ("_") for each checkbox. By doing this, you
      are effectively telling Spring that <quote>
          <emphasis>the checkbox was visible in the form and I want my object
          to which the form data will be bound to reflect the state of the
          checkbox no matter what</emphasis>
        </quote>.</para>

      <section id="view-jsp-formtaglib-checkboxestag">
        <title>The <literal>checkboxes</literal> tag</title>

        <para>This tag renders multiple HTML 'input' tags with type
        'checkbox'.</para>

        <para>Building on the example from the previous
        <classname>checkbox</classname> tag section. Sometimes you prefer not
        to have to list all the possible hobbies in your JSP page. You would
        rather provide a list at runtime of the available options and pass
        that in to the tag. That is the purpose of the
        <classname>checkboxes</classname> tag. You pass in an
        <classname>Array</classname>, a <classname>List</classname> or a
        <classname>Map</classname> containing the available options in the
        "items" property. Typically the bound property is a collection so it
        can hold multiple values selected by the user. Below is an example of
        the JSP using this tag:</para>
      </section>

      <programlisting language="xml">&lt;form:form&gt;
      &lt;table&gt;
          &lt;tr&gt;
              &lt;td&gt;Interests:&lt;/td&gt;
              &lt;td&gt;
                  <lineannotation>&lt;%-- Property is of an array or of type <interfacename>java.util.Collection</interfacename> --%&gt;</lineannotation>
                  &lt;form:checkboxes path="preferences.interests" items="${interestList}"/&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
      &lt;/table&gt;
  &lt;/form:form&gt;</programlisting>

      <para>This example assumes that the "interestList" is a
      <classname>List</classname> available as a model attribute containing
      strings of the values to be selected from. In the case where you use a
      Map, the map entry key will be used as the value and the map entry's
      value will be used as the label to be displayed. You can also use a
      custom object where you can provide the property names for the value
      using "itemValue" and the label using "itemLabel".</para>

      <section id="view-jsp-formtaglib-radiobuttontag">
        <title>The <literal>radiobutton</literal> tag</title>

        <para>This tag renders an HTML 'input' tag with type 'radio'.</para>

        <para>A typical usage pattern will involve multiple tag instances
        bound to the same property but with different values.</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Sex:&lt;/td&gt;
      &lt;td&gt;Male: &lt;form:radiobutton path="sex" value="M"/&gt; &lt;br/&gt;
          Female: &lt;form:radiobutton path="sex" value="F"/&gt; &lt;/td&gt;
  &lt;/tr&gt;</programlisting>
      </section>

      <section id="view-jsp-formtaglib-radiobuttonstag">
        <title>The <literal>radiobuttons</literal> tag</title>

        <para>This tag renders multiple HTML 'input' tags with type
        'radio'.</para>

        <para>Just like the <classname>checkboxes</classname> tag above, you
        might want to pass in the available options as a runtime variable. For
        this usage you would use the <classname>radiobuttons</classname> tag.
        You pass in an <classname>Array</classname>, a
        <classname>List</classname> or a <classname>Map</classname> containing
        the available options in the "items" property. In the case where you
        use a Map, the map entry key will be used as the value and the map
        entry's value will be used as the label to be displayed. You can also
        use a custom object where you can provide the property names for the
        value using "itemValue" and the label using "itemLabel".</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Sex:&lt;/td&gt;
      &lt;td&gt;&lt;form:radiobuttons path="sex" items="${sexOptions}"/&gt;&lt;/td&gt;
  &lt;/tr&gt;</programlisting>
      </section>

      <section id="view-jsp-formtaglib-passwordtag">
        <title>The <literal>password</literal> tag</title>

        <para>This tag renders an HTML 'input' tag with type 'password' using
        the bound value.</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Password:&lt;/td&gt;
      &lt;td&gt;
          &lt;form:password path="password" /&gt;
      &lt;/td&gt;
  &lt;/tr&gt;</programlisting>

        <para>Please note that by default, the password value is
        <emphasis>not</emphasis> shown. If you do want the password value to
        be shown, then set the value of the <literal>'showPassword'</literal>
        attribute to true, like so.</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Password:&lt;/td&gt;
      &lt;td&gt;
          &lt;form:password path="password" value="^76525bvHGq" showPassword="true" /&gt;
      &lt;/td&gt;
  &lt;/tr&gt;</programlisting>
      </section>

      <section id="view-jsp-formtaglib-selecttag">
        <title>The <literal>select</literal> tag</title>

        <para>This tag renders an HTML 'select' element. It supports data
        binding to the selected option as well as the use of nested
        <literal>option</literal> and <literal>options</literal> tags.</para>

        <para>Let's assume a <classname>User</classname> has a list of
        skills.</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Skills:&lt;/td&gt;
      &lt;td&gt;&lt;form:select path="skills" items="${skills}"/&gt;&lt;/td&gt;
  &lt;/tr&gt;</programlisting>

        <para>If the <literal>User's</literal> skill were in Herbology, the
        HTML source of the 'Skills' row would look like:</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Skills:&lt;/td&gt;
      &lt;td&gt;&lt;select name="skills" multiple="true"&gt;
          &lt;option value="Potions"&gt;Potions&lt;/option&gt;
          &lt;option value="Herbology" selected="selected"&gt;Herbology&lt;/option&gt;
          &lt;option value="Quidditch"&gt;Quidditch&lt;/option&gt;&lt;/select&gt;
      &lt;/td&gt;
  &lt;/tr&gt;</programlisting>
      </section>

      <section id="view-jsp-formtaglib-optiontag">
        <title>The <literal>option</literal> tag</title>

        <para>This tag renders an HTML 'option'. It sets 'selected' as
        appropriate based on the bound value.</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;House:&lt;/td&gt;
      &lt;td&gt;
          &lt;form:select path="house"&gt;
              &lt;form:option value="Gryffindor"/&gt;
              &lt;form:option value="Hufflepuff"/&gt;
              &lt;form:option value="Ravenclaw"/&gt;
              &lt;form:option value="Slytherin"/&gt;
          &lt;/form:select&gt;
      &lt;/td&gt;
  &lt;/tr&gt;</programlisting>

        <para>If the <literal>User's</literal> house was in Gryffindor, the
        HTML source of the 'House' row would look like:</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;House:&lt;/td&gt;
      &lt;td&gt;
          &lt;select name="house"&gt;
              &lt;option value="Gryffindor" selected="selected"&gt;Gryffindor&lt;/option&gt;
              &lt;option value="Hufflepuff"&gt;Hufflepuff&lt;/option&gt;
              &lt;option value="Ravenclaw"&gt;Ravenclaw&lt;/option&gt;
              &lt;option value="Slytherin"&gt;Slytherin&lt;/option&gt;
          &lt;/select&gt;
      &lt;/td&gt;
   &lt;/tr&gt;</programlisting>
      </section>

      <section id="view-jsp-formtaglib-optionstag">
        <title>The <literal>options</literal> tag</title>

        <para>This tag renders a list of HTML 'option' tags. It sets the
        'selected' attribute as appropriate based on the bound value.</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Country:&lt;/td&gt;
      &lt;td&gt;
          &lt;form:select path="country"&gt;
              &lt;form:option value="-" label="--Please Select"/&gt;
              &lt;form:options items="${countryList}" itemValue="code" itemLabel="name"/&gt;
          &lt;/form:select&gt;
      &lt;/td&gt;
  &lt;/tr&gt;</programlisting>

        <para>If the <classname>User</classname> lived in the UK, the HTML
        source of the 'Country' row would look like:</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Country:&lt;/td&gt;
      &lt;td&gt;
          &lt;select name="country"&gt;
              &lt;option value="-"&gt;--Please Select&lt;/option&gt;
              &lt;option value="AT"&gt;Austria&lt;/option&gt;
              &lt;option value="UK" selected="selected"&gt;United Kingdom&lt;/option&gt;
              &lt;option value="US"&gt;United States&lt;/option&gt;
          &lt;/select&gt;
      &lt;/td&gt;
  &lt;/tr&gt;</programlisting>

        <para>As the example shows, the combined usage of an
        <literal>option</literal> tag with the <literal>options</literal> tag
        generates the same standard HTML, but allows you to explicitly specify
        a value in the JSP that is for display only (where it belongs) such as
        the default string in the example: "-- Please Select".</para>

        <para>The <literal>items</literal> attribute is typically populated
        with a collection or array of item objects.
        <literal>itemValue</literal> and <literal>itemLabel</literal> simply
        refer to bean properties of those item objects, if specified;
        otherwise, the item objects themselves will be stringified.
        Alternatively, you may specify a <literal>Map</literal> of items, in
        which case the map keys are interpreted as option values and the map
        values correspond to option labels. If <literal>itemValue</literal>
        and/or <literal>itemLabel</literal> happen to be specified as well,
        the item value property will apply to the map key and the item label
        property will apply to the map value.</para>
      </section>

      <section id="view-jsp-formtaglib-textAreatag">
        <title>The <literal>textarea</literal> tag</title>

        <para>This tag renders an HTML 'textarea'.</para>

        <programlisting language="xml">&lt;tr&gt;
      &lt;td&gt;Notes:&lt;/td&gt;
      &lt;td&gt;&lt;form:textarea path="notes" rows="3" cols="20" /&gt;&lt;/td&gt;
      &lt;td&gt;&lt;form:errors path="notes" /&gt;&lt;/td&gt;
  &lt;/tr&gt;</programlisting>
      </section>

      <section id="view-jsp-formtaglib-hiddeninputtag">
        <title>The <literal>hidden</literal> tag</title>

        <para>This tag renders an HTML 'input' tag with type 'hidden' using
        the bound value. To submit an unbound hidden value, use the HTML
        <literal>input</literal> tag with type 'hidden'.</para>

        <programlisting language="xml">&lt;form:hidden path="house" /&gt;
  </programlisting>

        <para>If we choose to submit the 'house' value as a hidden one, the
        HTML would look like:</para>

        <programlisting language="xml">&lt;input name="house" type="hidden" value="Gryffindor"/&gt;
  </programlisting>
      </section>

      <section id="view-jsp-formtaglib-errorstag">
        <title>The <literal>errors</literal> tag</title>

        <para>This tag renders field errors in an HTML 'span' tag. It provides
        access to the errors created in your controller or those that were
        created by any validators associated with your controller.</para>

        <para>Let's assume we want to display all error messages for the
        <literal>firstName</literal> and <literal>lastName</literal> fields
        once we submit the form. We have a validator for instances of the
        <classname>User</classname> class called
        <classname>UserValidator</classname>.</para>

        <programlisting language="java">public class UserValidator implements Validator {

      public boolean supports(Class candidate) {
          return User.class.isAssignableFrom(candidate);
      }

      public void validate(Object obj, Errors errors) {
          ValidationUtils.rejectIfEmptyOrWhitespace(errors, "firstName", "required", "Field is required.");
          ValidationUtils.rejectIfEmptyOrWhitespace(errors, "lastName", "required", "Field is required.");
      }
  }</programlisting>

        <para>The <literal>form.jsp</literal> would look like:</para>

        <programlisting language="xml">&lt;form:form&gt;
      &lt;table&gt;
          &lt;tr&gt;
              &lt;td&gt;First Name:&lt;/td&gt;
              &lt;td&gt;&lt;form:input path="firstName" /&gt;&lt;/td&gt;
              <lineannotation>&lt;%-- Show errors for firstName field --%&gt;</lineannotation>
              &lt;td&gt;&lt;form:errors path="firstName" /&gt;&lt;/td&gt;
          &lt;/tr&gt;

          &lt;tr&gt;
              &lt;td&gt;Last Name:&lt;/td&gt;
              &lt;td&gt;&lt;form:input path="lastName" /&gt;&lt;/td&gt;
              <lineannotation>&lt;%-- Show errors for lastName field --%&gt;</lineannotation>
              &lt;td&gt;&lt;form:errors path="lastName"  /&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td colspan="3"&gt;
                  &lt;input type="submit" value="Save Changes" /&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
      &lt;/table&gt;
  &lt;/form:form&gt;</programlisting>

        <para>If we submit a form with empty values in the
        <literal>firstName</literal> and <literal>lastName</literal> fields,
        this is what the HTML would look like:</para>

        <programlisting language="xml">&lt;form method="POST"&gt;
      &lt;table&gt;
          &lt;tr&gt;
              &lt;td&gt;First Name:&lt;/td&gt;
              &lt;td&gt;&lt;input name="firstName" type="text" value=""/&gt;&lt;/td&gt;
              <lineannotation>&lt;%-- Associated errors to firstName field displayed --%&gt;</lineannotation>
              &lt;td&gt;&lt;span name="firstName.errors"&gt;Field is required.&lt;/span&gt;&lt;/td&gt;
          &lt;/tr&gt;

          &lt;tr&gt;
              &lt;td&gt;Last Name:&lt;/td&gt;
              &lt;td&gt;&lt;input name="lastName" type="text" value=""/&gt;&lt;/td&gt;
              <lineannotation>&lt;%-- Associated errors to lastName field displayed --%&gt;</lineannotation>
              &lt;td&gt;&lt;span name="lastName.errors"&gt;Field is required.&lt;/span&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td colspan="3"&gt;
                  &lt;input type="submit" value="Save Changes" /&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
      &lt;/table&gt;
  &lt;/form&gt;</programlisting>

        <para>What if we want to display the entire list of errors for a given
        page? The example below shows that the <literal>errors</literal> tag
        also supports some basic wildcarding functionality.</para>

        <itemizedlist>
          <listitem>
            <para><literal>path="*"</literal> - displays all errors</para>
          </listitem>

          <listitem>
            <para><literal>path="lastName*"</literal> - displays all errors
            associated with the <literal>lastName</literal> field</para>
          </listitem>
        </itemizedlist>

        <para>The example below will display a list of errors at the top of
        the page, followed by field-specific errors next to the fields:</para>

        <programlisting language="xml">&lt;form:form&gt;
      &lt;form:errors path="*" cssClass="errorBox" /&gt;
      &lt;table&gt;
          &lt;tr&gt;
              &lt;td&gt;First Name:&lt;/td&gt;
              &lt;td&gt;&lt;form:input path="firstName" /&gt;&lt;/td&gt;
              &lt;td&gt;&lt;form:errors path="firstName" /&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td&gt;Last Name:&lt;/td&gt;
              &lt;td&gt;&lt;form:input path="lastName" /&gt;&lt;/td&gt;
              &lt;td&gt;&lt;form:errors path="lastName"  /&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td colspan="3"&gt;
                  &lt;input type="submit" value="Save Changes" /&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
      &lt;/table&gt;
  &lt;/form:form&gt;</programlisting>

        <para>The HTML would look like:</para>

        <programlisting language="xml">&lt;form method="POST"&gt;
      &lt;span name="*.errors" class="errorBox"&gt;Field is required.&lt;br/&gt;Field is required.&lt;/span&gt;
      &lt;table&gt;
          &lt;tr&gt;
              &lt;td&gt;First Name:&lt;/td&gt;
              &lt;td&gt;&lt;input name="firstName" type="text" value=""/&gt;&lt;/td&gt;
              &lt;td&gt;&lt;span name="firstName.errors"&gt;Field is required.&lt;/span&gt;&lt;/td&gt;
          &lt;/tr&gt;

          &lt;tr&gt;
              &lt;td&gt;Last Name:&lt;/td&gt;
              &lt;td&gt;&lt;input name="lastName" type="text" value=""/&gt;&lt;/td&gt;
              &lt;td&gt;&lt;span name="lastName.errors"&gt;Field is required.&lt;/span&gt;&lt;/td&gt;
          &lt;/tr&gt;
          &lt;tr&gt;
              &lt;td colspan="3"&gt;
                  &lt;input type="submit" value="Save Changes" /&gt;
              &lt;/td&gt;
          &lt;/tr&gt;
  &lt;/form&gt;</programlisting>
      </section>

      <section id="rest-method-conversion">
        <title>HTTP Method Conversion</title>

        <para>A key principle of REST is the use of the Uniform Interface.
        This means that all resources (URLs) can be manipulated using the same
        four HTTP methods: GET, PUT, POST, and DELETE. For each methods, the
        HTTP specification defines the exact semantics. For instance, a GET
        should always be a safe operation, meaning that is has no side
        effects, and a PUT or DELETE should be idempotent, meaning that you
        can repeat these operations over and over again, but the end result
        should be the same. While HTTP defines these four methods, HTML only
        supports two: GET and POST. Fortunately, there are two possible
        workarounds: you can either use JavaScript to do your PUT or DELETE,
        or simply do a POST with the 'real' method as an additional parameter
        (modeled as a hidden input field in an HTML form). This latter trick
        is what Spring's <classname>HiddenHttpMethodFilter</classname> does.
        This filter is a plain Servlet Filter and therefore it can be used in
        combination with any web framework (not just Spring MVC). Simply add
        this filter to your web.xml, and a POST with a hidden _method
        parameter will be converted into the corresponding HTTP method
        request.</para>

        <para>To support HTTP method conversion the Spring MVC form tag was
        updated to support setting the HTTP method. For example, the following
        snippet taken from the updated Petclinic sample</para>

        <programlisting language="xml">&lt;form:form method="delete"&gt;
      &lt;p class="submit"&gt;&lt;input type="submit" value="Delete Pet"/&gt;&lt;/p&gt;
&lt;/form:form&gt;</programlisting>

        <para>This will actually perform an HTTP POST, with the 'real' DELETE
        method hidden behind a request parameter, to be picked up by the
        <classname>HiddenHttpMethodFilter</classname>, as defined in web.xml:</para>
        <programlisting language="java">&lt;filter&gt;
    &lt;filter-name&gt;httpMethodFilter&lt;/filter-name&gt;
    &lt;filter-class&gt;org.springframework.web.filter.HiddenHttpMethodFilter&lt;/filter-class&gt;
&lt;/filter&gt;

&lt;filter-mapping&gt;
    &lt;filter-name&gt;httpMethodFilter&lt;/filter-name&gt;
    &lt;servlet-name&gt;petclinic&lt;/servlet-name&gt;
&lt;/filter-mapping&gt;</programlisting><para>The corresponding @Controller method
        is shown below:</para>

        <programlisting language="java">@RequestMapping(method = RequestMethod.DELETE)
public String deletePet(@PathVariable int ownerId, @PathVariable int petId) {
  this.clinic.deletePet(petId);
  return "redirect:/owners/" + ownerId;
}</programlisting>
      </section>
    </section>
  </section>

  <section id="view-tiles">
    <title>Tiles</title>

    <para>It is possible to integrate Tiles - just as any other view
    technology - in web applications using Spring. The following describes in
    a broad way how to do this.</para>

    <para><emphasis>NOTE:</emphasis> This section focuses on Spring's support
    for Tiles 2 (the standalone version of Tiles, requiring Java 5+) in the
    <literal>org.springframework.web.servlet.view.tiles2</literal> package.
    Spring also continues to support Tiles 1.x (a.k.a. "Struts Tiles", as
    shipped with Struts 1.1+; compatible with Java 1.4) in the original
    <literal>org.springframework.web.servlet.view.tiles</literal>
    package.</para>

    <section id="view-tiles-dependencies">
      <title>Dependencies</title>

      <para>To be able to use Tiles you have to have a couple of additional
      dependencies included in your project. The following is the list of
      dependencies you need.</para>

      <para><itemizedlist spacing="compact">
          <listitem>
            <para><literal>Tiles version 2.0.4 or higher</literal></para>
          </listitem>

          <listitem>
            <para><literal>Commons BeanUtils</literal></para>
          </listitem>

          <listitem>
            <para><literal>Commons Digester</literal></para>
          </listitem>

          <listitem>
            <para><literal>Commons Logging</literal></para>
          </listitem>
        </itemizedlist></para>

      <para>These dependencies are all available in the Spring
      distribution.</para>
    </section>

    <section id="view-tiles-integrate">
      <title>How to integrate Tiles</title>

      <para>To be able to use Tiles, you have to configure it using files
      containing definitions (for basic information on definitions and other
      Tiles concepts, please have a look at <ulink
      url="http://tiles.apache.org" />). In Spring this is done using the
      <classname>TilesConfigurer</classname>. Have a look at the following
      piece of example ApplicationContext configuration:</para>

      <programlisting language="xml">&lt;bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles2.TilesConfigurer"&gt;
  &lt;property name="definitions"&gt;
    &lt;list&gt;
      &lt;value&gt;/WEB-INF/defs/general.xml&lt;/value&gt;
      &lt;value&gt;/WEB-INF/defs/widgets.xml&lt;/value&gt;
      &lt;value&gt;/WEB-INF/defs/administrator.xml&lt;/value&gt;
      &lt;value&gt;/WEB-INF/defs/customer.xml&lt;/value&gt;
      &lt;value&gt;/WEB-INF/defs/templates.xml&lt;/value&gt;
    &lt;/list&gt;
  &lt;/property&gt;
&lt;/bean&gt;</programlisting>

      <para>As you can see, there are five files containing definitions, which
      are all located in the <filename
      class="directory">'WEB-INF/defs'</filename> directory. At initialization
      of the <interfacename>WebApplicationContext</interfacename>, the files
      will be loaded and the definitions factory will be initialized. After
      that has been done, the Tiles includes in the definition files can be
      used as views within your Spring web application. To be able to use the
      views you have to have a <interfacename>ViewResolver</interfacename>
      just as with any other view technology used with Spring. Below you can
      find two possibilities, the <classname>UrlBasedViewResolver</classname>
      and the <classname>ResourceBundleViewResolver</classname>.</para>

      <section id="view-tiles-url">
        <title>
          <classname>UrlBasedViewResolver</classname>
        </title>

        <para>The <classname>UrlBasedViewResolver</classname> instantiates the
        given <literal>viewClass</literal> for each view it has to
        resolve.</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.tiles2.TilesView"/&gt;
&lt;/bean&gt;</programlisting>
      </section>

      <section id="view-tiles-resource">
        <title>
          <classname>ResourceBundleViewResolver</classname>
        </title>

        <para>The <classname>ResourceBundleViewResolver</classname> has to be
        provided with a property file containing viewnames and viewclasses the
        resolver can use:</para>

        <programlisting language="xml">&lt;bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"&gt;
  &lt;property name="basename" value="views"/&gt;
&lt;/bean&gt;</programlisting>

        <programlisting language="java">...
welcomeView.class=org.springframework.web.servlet.view.tiles2.TilesView
welcomeView.url=welcome <lineannotation>(this is the name of a Tiles definition)</lineannotation>

vetsView.class=org.springframework.web.servlet.view.tiles2.TilesView
vetsView.url=vetsView <lineannotation>(again, this is the name of a Tiles definition)</lineannotation>

findOwnersForm.class=org.springframework.web.servlet.view.JstlView
findOwnersForm.url=/WEB-INF/jsp/findOwners.jsp
...</programlisting>

        <para>As you can see, when using the
        <classname>ResourceBundleViewResolver</classname>, you can easily mix
        different view technologies.</para>
      </section>

      <para>Note that the <classname>TilesView</classname> class for Tiles 2
      supports JSTL (the JSP Standard Tag Library) out of the box, whereas
      there is a separate <classname>TilesJstlView</classname> subclass in the
      Tiles 1.x support.</para>

      <section id="view-tiles-preparer">
        <title><classname>SimpleSpringPreparerFactory</classname> and
        <classname>SpringBeanPreparerFactory</classname></title>

        <para>As an advanced feature, Spring also supports two special Tiles 2
        <interfacename>PreparerFactory</interfacename> implementations. Check
        out the Tiles documentation for details on how to use
        <interfacename>ViewPreparer</interfacename> references in your Tiles
        definition files.</para>

        <para>Specify <classname>SimpleSpringPreparerFactory</classname> to
        autowire ViewPreparer instances based on specified preparer classes,
        applying Spring's container callbacks as well as applying configured
        Spring BeanPostProcessors. If Spring's context-wide annotation-config
        has been activated, annotations in ViewPreparer classes will be
        automatically detected and applied. Note that this expects preparer
        <emphasis>classes</emphasis> in the Tiles definition files, just like
        the default <classname>PreparerFactory</classname> does.</para>

        <para>Specify <classname>SpringBeanPreparerFactory</classname> to
        operate on specified preparer <emphasis>names</emphasis> instead of
        classes, obtaining the corresponding Spring bean from the
        DispatcherServlet's application context. The full bean creation
        process will be in the control of the Spring application context in
        this case, allowing for the use of explicit dependency injection
        configuration, scoped beans etc. Note that you need to define one
        Spring bean definition per preparer name (as used in your Tiles
        definitions).</para>

        <programlisting language="xml">&lt;bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles2.TilesConfigurer"&gt;
  &lt;property name="definitions"&gt;
    &lt;list&gt;
      &lt;value&gt;/WEB-INF/defs/general.xml&lt;/value&gt;
      &lt;value&gt;/WEB-INF/defs/widgets.xml&lt;/value&gt;
      &lt;value&gt;/WEB-INF/defs/administrator.xml&lt;/value&gt;
      &lt;value&gt;/WEB-INF/defs/customer.xml&lt;/value&gt;
      &lt;value&gt;/WEB-INF/defs/templates.xml&lt;/value&gt;
    &lt;/list&gt;
  &lt;/property&gt;

  <lineannotation>&lt;!-- resolving preparer names as Spring bean definition names --&gt;</lineannotation>
  &lt;property name="preparerFactoryClass"
       value="org.springframework.web.servlet.view.tiles2.SpringBeanPreparerFactory"/&gt;

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

  <section id="view-velocity">
    <title>Velocity &amp; FreeMarker</title>

    <para><ulink url="http://velocity.apache.org">Velocity</ulink> and <ulink
    url="http://www.freemarker.org">FreeMarker</ulink> are two templating
    languages that can both be used as view technologies within Spring MVC
    applications. The languages are quite similar and serve similar needs and
    so are considered together in this section. For semantic and syntactic
    differences between the two languages, see the <ulink
    url="http://www.freemarker.org">FreeMarker</ulink> web site.</para>

    <section id="view-velocity-dependencies">
      <title>Dependencies</title>

      <para>Your web application will need to include <filename
      class="libraryfile">velocity-1.x.x.jar</filename> or <filename
      class="libraryfile">freemarker-2.x.jar</filename> in order to work with
      Velocity or FreeMarker respectively and <filename
      class="libraryfile">commons-collections.jar</filename> needs also to be
      available for Velocity. Typically they are included in the
      <literal>WEB-INF/lib</literal> folder where they are guaranteed to be
      found by a Java EE server and added to the classpath for your application.
      It is of course assumed that you already have the <filename
      class="libraryfile">spring.jar</filename> in your <filename
      class="directory">'WEB-INF/lib'</filename> directory too! The latest
      stable Velocity, FreeMarker and Commons Collections jars are supplied
      with the Spring framework and can be copied from the relevant <filename
      class="libraryfile">/lib/</filename> sub-directories. If you make use of
      Spring's 'dateToolAttribute' or 'numberToolAttribute' in your Velocity
      views, you will also need to include the <filename
      class="libraryfile">velocity-tools-generic-1.x.jar</filename></para>
    </section>

    <section id="view-velocity-contextconfig">
      <title>Context configuration</title>

      <para>A suitable configuration is initialized by adding the relevant
      configurer bean definition to your <filename>'*-servlet.xml'</filename>
      as shown below:</para>

      <programlisting language="xml"><lineannotation>&lt;!-- 
  This bean sets up the Velocity environment for us based on a root path for templates.
  Optionally, a properties file can be specified for more control over the Velocity
  environment, but the defaults are pretty sane for file based template loading.
--&gt;</lineannotation>
&lt;bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer"&gt;
  &lt;property name="resourceLoaderPath" value="/WEB-INF/velocity/"/&gt;
&lt;/bean&gt;

<lineannotation>&lt;!-- 

  View resolvers can also be configured with ResourceBundles or XML files. If you need
  different view resolving based on Locale, you have to use the resource bundle resolver.

--&gt;</lineannotation>
&lt;bean id="viewResolver" class="org.springframework.web.servlet.view.velocity.VelocityViewResolver"&gt;
  &lt;property name="cache" value="true"/&gt;
  &lt;property name="prefix" value=""/&gt;
  &lt;property name="suffix" value=".vm"/&gt;
&lt;/bean&gt;</programlisting>

      <programlisting><lineannotation>&lt;!-- freemarker config --&gt;</lineannotation>
&lt;bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer"&gt;
  &lt;property name="templateLoaderPath" value="/WEB-INF/freemarker/"/&gt;
&lt;/bean&gt;

<lineannotation>&lt;!-- 

  View resolvers can also be configured with ResourceBundles or XML files. If you need
  different view resolving based on Locale, you have to use the resource bundle resolver.

--&gt;</lineannotation>
&lt;bean id="viewResolver" class="org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver"&gt;
  &lt;property name="cache" value="true"/&gt;
  &lt;property name="prefix" value=""/&gt;
  &lt;property name="suffix" value=".ftl"/&gt;
&lt;/bean&gt;</programlisting>

      <note>
        <para>For non web-apps add a
        <classname>VelocityConfigurationFactoryBean</classname> or a
        <classname>FreeMarkerConfigurationFactoryBean</classname> to your
        application context definition file.</para>
      </note>
    </section>

    <section id="view-velocity-createtemplates">
      <title>Creating templates</title>

      <para>Your templates need to be stored in the directory specified by the
      <literal>*Configurer</literal> bean shown above. This document does not
      cover details of creating templates for the two languages - please see
      their relevant websites for information. If you use the view resolvers
      highlighted, then the logical view names relate to the template file
      names in similar fashion to
      <classname>InternalResourceViewResolver</classname> for JSP's. So if
      your controller returns a ModelAndView object containing a view name of
      "welcome" then the resolvers will look for the
      <literal>/WEB-INF/freemarker/welcome.ftl</literal> or
      <literal>/WEB-INF/velocity/welcome.vm</literal> template as
      appropriate.</para>
    </section>

    <section id="view-velocity-advancedconfig">
      <title>Advanced configuration</title>

      <para>The basic configurations highlighted above will be suitable for
      most application requirements, however additional configuration options
      are available for when unusual or advanced requirements dictate.</para>

      <section id="view-velocity-example-velocityproperties">
        <title>velocity.properties</title>

        <para>This file is completely optional, but if specified, contains the
        values that are passed to the Velocity runtime in order to configure
        velocity itself. Only required for advanced configurations, if you
        need this file, specify its location on the
        <literal>VelocityConfigurer</literal> bean definition above.</para>

        <programlisting language="xml">&lt;bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer"&gt;
  &lt;property name="configLocation value="/WEB-INF/velocity.properties"/&gt;
&lt;/bean&gt;</programlisting>

        <para>Alternatively, you can specify velocity properties directly in
        the bean definition for the Velocity config bean by replacing the
        "configLocation" property with the following inline properties.</para>

        <programlisting language="xml">&lt;bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer"&gt;
  &lt;property name="velocityProperties"&gt;
    &lt;props&gt;
      &lt;prop key="resource.loader"&gt;file&lt;/prop&gt;
      &lt;prop key="file.resource.loader.class"&gt;
        org.apache.velocity.runtime.resource.loader.FileResourceLoader
      &lt;/prop&gt;
      &lt;prop key="file.resource.loader.path"&gt;${webapp.root}/WEB-INF/velocity&lt;/prop&gt;
      &lt;prop key="file.resource.loader.cache"&gt;false&lt;/prop&gt;
    &lt;/props&gt;
  &lt;/property&gt;
&lt;/bean&gt;</programlisting>

        <para>Refer to the <ulink
        url="http://static.springframework.org/spring/docs/2.5.x/api/org/springframework/ui/velocity/VelocityEngineFactory.html">API
        documentation</ulink> for Spring configuration of Velocity, or the
        Velocity documentation for examples and definitions of the
        <filename>'velocity.properties'</filename> file itself.</para>
      </section>

      <section id="views-freemarker">
        <title>FreeMarker</title>

        <para>FreeMarker 'Settings' and 'SharedVariables' can be passed
        directly to the FreeMarker <literal>Configuration</literal> object
        managed by Spring by setting the appropriate bean properties on the
        <literal>FreeMarkerConfigurer</literal> bean. The
        <literal>freemarkerSettings</literal> property requires a
        <literal>java.util.Properties</literal> object and the
        <literal>freemarkerVariables</literal> property requires a
        <literal>java.util.Map</literal>.</para>

        <programlisting language="xml">&lt;bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer"&gt;
  &lt;property name="templateLoaderPath" value="/WEB-INF/freemarker/"/&gt;
  &lt;property name="freemarkerVariables"&gt;
    &lt;map&gt;
      &lt;entry key="xml_escape" value-ref="fmXmlEscape"/&gt;
    &lt;/map&gt;
  &lt;/property&gt;
&lt;/bean&gt;

&lt;bean id="fmXmlEscape" class="freemarker.template.utility.XmlEscape"/&gt;</programlisting>

        <para>See the FreeMarker documentation for details of settings and
        variables as they apply to the <classname>Configuration</classname>
        object.</para>
      </section>
    </section>

    <section id="view-velocity-forms">
      <title>Bind support and form handling</title>

      <para>Spring provides a tag library for use in JSP's that contains
      (amongst other things) a <literal>&lt;spring:bind/&gt;</literal> tag.
      This tag primarily enables forms to display values from form backing
      objects and to show the results of failed validations from a
      <literal>Validator</literal> in the web or business tier. From version
      1.1, Spring now has support for the same functionality in both Velocity
      and FreeMarker, with additional convenience macros for generating form
      input elements themselves.</para>

      <section id="view-bind-macros">
        <title>The bind macros</title>

        <para>A standard set of macros are maintained within the
        <literal>spring.jar</literal> file for both languages, so they are
        always available to a suitably configured application.</para>

        <para>Some of the macros defined in the Spring libraries are
        considered internal (private) but no such scoping exists in the macro
        definitions making all macros visible to calling code and user
        templates. The following sections concentrate only on the macros you
        need to be directly calling from within your templates. If you wish to
        view the macro code directly, the files are called spring.vm /
        spring.ftl and are in the packages
        <literal>org.springframework.web.servlet.view.velocity</literal> or
        <literal>org.springframework.web.servlet.view.freemarker</literal>
        respectively.</para>
      </section>

      <section id="view-simple-binding">
        <title>Simple binding</title>

        <para>In your html forms (vm / ftl templates) that act as the
        'formView' for a Spring form controller, you can use code similar to
        the following to bind to field values and display error messages for
        each input field in similar fashion to the JSP equivalent. Note that
        the name of the command object is "command" by default, but can be
        overridden in your MVC configuration by setting the 'commandName' bean
        property on your form controller. Example code is shown below for the
        <literal>personFormV</literal> and <literal>personFormF</literal>
        views configured earlier;</para>

        <programlisting language="xml">&lt;!-- velocity macros are automatically available --&gt;
&lt;html&gt;
...
&lt;form action="" method="POST"&gt;
  Name: 
  #springBind( "command.name" )
  &lt;input type="text" 
    name="${status.expression}" 
    value="$!status.value" /&gt;&lt;br&gt;
  #foreach($error in $status.errorMessages) &lt;b&gt;$error&lt;/b&gt; &lt;br&gt; #end
  &lt;br&gt;
  ... 
  &lt;input type="submit" value="submit"/&gt;
&lt;/form&gt;
...
&lt;/html&gt;</programlisting>

        <programlisting language="xml">&lt;!-- freemarker macros have to be imported into a namespace.  We strongly
recommend sticking to 'spring' --&gt;
&lt;#import "spring.ftl" as spring /&gt;
&lt;html&gt;
...
&lt;form action="" method="POST"&gt;
  Name: 
  &lt;@spring.bind "command.name" /&gt; 
  &lt;input type="text" 
    name="${spring.status.expression}" 
    value="${spring.status.value?default("")}" /&gt;&lt;br&gt;
  &lt;#list spring.status.errorMessages as error&gt; &lt;b&gt;${error}&lt;/b&gt; &lt;br&gt; &lt;/#list&gt;
  &lt;br&gt;
  ... 
  &lt;input type="submit" value="submit"/&gt;
&lt;/form&gt;
...
&lt;/html&gt;</programlisting>

        <para><literal>#springBind</literal> /
        <literal>&lt;@spring.bind&gt;</literal> requires a 'path' argument
        which consists of the name of your command object (it will be
        'command' unless you changed it in your FormController properties)
        followed by a period and the name of the field on the command object
        you wish to bind to. Nested fields can be used too such as
        "command.address.street". The <literal>bind</literal> macro assumes
        the default HTML escaping behavior specified by the ServletContext
        parameter <literal>defaultHtmlEscape</literal> in web.xml</para>

        <para>The optional form of the macro called
        <literal>#springBindEscaped</literal> /
        <literal>&lt;@spring.bindEscaped&gt;</literal> takes a second argument
        and explicitly specifies whether HTML escaping should be used in the
        status error messages or values. Set to true or false as required.
        Additional form handling macros simplify the use of HTML escaping and
        these macros should be used wherever possible. They are explained in
        the next section.</para>
      </section>

      <section id="views-form-macros">
        <title>Form input generation macros</title>

        <para>Additional convenience macros for both languages simplify both
        binding and form generation (including validation error display). It
        is never necessary to use these macros to generate form input fields,
        and they can be mixed and matched with simple HTML or calls direct to
        the spring bind macros highlighted previously.</para>

        <para>The following table of available macros show the VTL and FTL
        definitions and the parameter list that each takes.</para>

        <table id="views-macros-defs-tbl">
          <title>Table of macro definitions</title>

          <tgroup cols="3">
            <colspec align="left" />

            <thead>
              <row>
                <entry align="center">macro</entry>

                <entry align="center">VTL definition</entry>

                <entry align="center">FTL definition</entry>
              </row>
            </thead>

            <tbody>
              <row>
                <entry><emphasis role="bold">message</emphasis> (output a
                string from a resource bundle based on the code
                parameter)</entry>

                <entry><literal>#springMessage($code)</literal></entry>

                <entry><literal>&lt;@spring.message
                code/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">messageText</emphasis> (output a
                string from a resource bundle based on the code parameter,
                falling back to the value of the default parameter)</entry>

                <entry><literal>#springMessageText($code
                $text)</literal></entry>

                <entry><literal>&lt;@spring.messageText code,
                text/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">url</emphasis> (prefix a relative
                URL with the application's context root)</entry>

                <entry><literal>#springUrl($relativeUrl)</literal></entry>

                <entry><literal>&lt;@spring.url
                relativeUrl/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">formInput</emphasis> (standard
                input field for gathering user input)</entry>

                <entry><literal>#springFormInput($path
                $attributes)</literal></entry>

                <entry><literal>&lt;@spring.formInput path, attributes,
                fieldType/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">formHiddenInput *</emphasis>
                (hidden input field for submitting non-user input)</entry>

                <entry><literal>#springFormHiddenInput($path
                $attributes)</literal></entry>

                <entry><literal>&lt;@spring.formHiddenInput path,
                attributes/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">formPasswordInput</emphasis> *
                (standard input field for gathering passwords. Note that no
                value will ever be populated in fields of this type)</entry>

                <entry><literal>#springFormPasswordInput($path
                $attributes)</literal></entry>

                <entry><literal>&lt;@spring.formPasswordInput path,
                attributes/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">formTextarea</emphasis> (large
                text field for gathering long, freeform text input)</entry>

                <entry><literal>#springFormTextarea($path
                $attributes)</literal></entry>

                <entry><literal>&lt;@spring.formTextarea path,
                attributes/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">formSingleSelect</emphasis> (drop
                down box of options allowing a single required value to be
                selected)</entry>

                <entry><literal>#springFormSingleSelect( $path $options
                $attributes)</literal></entry>

                <entry><literal>&lt;@spring.formSingleSelect path, options,
                attributes/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">formMultiSelect</emphasis> (a
                list box of options allowing the user to select 0 or more
                values)</entry>

                <entry><literal>#springFormMultiSelect($path $options
                $attributes)</literal></entry>

                <entry><literal>&lt;@spring.formMultiSelect path, options,
                attributes/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">formRadioButtons</emphasis> (a
                set of radio buttons allowing a single selection to be made
                from the available choices)</entry>

                <entry><literal>#springFormRadioButtons($path $options
                $separator $attributes)</literal></entry>

                <entry><literal>&lt;@spring.formRadioButtons path, options
                separator, attributes/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">formCheckboxes</emphasis> (a set
                of checkboxes allowing 0 or more values to be
                selected)</entry>

                <entry><literal>#springFormCheckboxes($path $options
                $separator $attributes)</literal></entry>

                <entry><literal>&lt;@spring.formCheckboxes path, options,
                separator, attributes/&gt;</literal></entry>
              </row>

              <row>
                <entry><emphasis role="bold">showErrors</emphasis> (simplify
                display of validation errors for the bound field)</entry>

                <entry><literal>#springShowErrors($separator
                $classOrStyle)</literal></entry>

                <entry><literal>&lt;@spring.showErrors separator,
                classOrStyle/&gt;</literal></entry>
              </row>
            </tbody>
          </tgroup>
        </table>

        <para>* In FTL (FreeMarker), these two macros are not actually
        required as you can use the normal <literal>formInput</literal> macro,
        specifying '<literal>hidden</literal>' or
        '<literal>password</literal>' as the value for the
        <literal>fieldType</literal> parameter.</para>

        <para>The parameters to any of the above macros have consistent
        meanings:</para>

        <itemizedlist>
          <listitem>
            <para>path: the name of the field to bind to (ie
            "command.name")</para>
          </listitem>

          <listitem>
            <para>options: a Map of all the available values that can be
            selected from in the input field. The keys to the map represent
            the values that will be POSTed back from the form and bound to the
            command object. Map objects stored against the keys are the labels
            displayed on the form to the user and may be different from the
            corresponding values posted back by the form. Usually such a map
            is supplied as reference data by the controller. Any Map
            implementation can be used depending on required behavior. For
            strictly sorted maps, a <literal>SortedMap</literal> such as a
            <literal>TreeMap</literal> with a suitable Comparator may be used
            and for arbitrary Maps that should return values in insertion
            order, use a <literal>LinkedHashMap</literal> or a
            <literal>LinkedMap</literal> from commons-collections.</para>
          </listitem>

          <listitem>
            <para>separator: where multiple options are available as discreet
            elements (radio buttons or checkboxes), the sequence of characters
            used to separate each one in the list (ie "&lt;br&gt;").</para>
          </listitem>

          <listitem>
            <para>attributes: an additional string of arbitrary tags or text
            to be included within the HTML tag itself. This string is echoed
            literally by the macro. For example, in a textarea field you may
            supply attributes as 'rows="5" cols="60"' or you could pass style
            information such as 'style="border:1px solid silver"'.</para>
          </listitem>

          <listitem>
            <para>classOrStyle: for the showErrors macro, the name of the CSS
            class that the span tag wrapping each error will use. If no
            information is supplied (or the value is empty) then the errors
            will be wrapped in &lt;b&gt;&lt;/b&gt; tags.</para>
          </listitem>
        </itemizedlist>

        <para>Examples of the macros are outlined below some in FTL and some
        in VTL. Where usage differences exist between the two languages, they
        are explained in the notes.</para>

        <section id="views-form-macros-input">
          <title>Input Fields</title>

          <para><programlisting language="xml">&lt;!-- the Name field example from above using form macros in VTL --&gt;
...
    Name:
    #springFormInput("command.name" "")&lt;br&gt;
    #springShowErrors("&lt;br&gt;" "")&lt;br&gt;</programlisting></para>

          <para>The formInput macro takes the path parameter (command.name)
          and an additional attributes parameter which is empty in the example
          above. The macro, along with all other form generation macros,
          performs an implicit spring bind on the path parameter. The binding
          remains valid until a new bind occurs so the showErrors macro
          doesn't need to pass the path parameter again - it simply operates
          on whichever field a bind was last created for.</para>

          <para>The showErrors macro takes a separator parameter (the
          characters that will be used to separate multiple errors on a given
          field) and also accepts a second parameter, this time a class name
          or style attribute. Note that FreeMarker is able to specify default
          values for the attributes parameter, unlike Velocity, and the two
          macro calls above could be expressed as follows in FTL:</para>

          <programlisting language="xml">&lt;@spring.formInput "command.name"/&gt;
&lt;@spring.showErrors "&lt;br&gt;"/&gt;</programlisting>

          <para>Output is shown below of the form fragment generating the name
          field, and displaying a validation error after the form was
          submitted with no value in the field. Validation occurs through
          Spring's Validation framework.</para>

          <para>The generated HTML looks like this:</para>

          <programlisting>Name:
  &lt;input type="text" name="name" value=""     
&gt;
&lt;br&gt;
  &lt;b&gt;required&lt;/b&gt;
&lt;br&gt;
&lt;br&gt;</programlisting>

          <para>The formTextarea macro works the same way as the formInput
          macro and accepts the same parameter list. Commonly, the second
          parameter (attributes) will be used to pass style information or
          rows and cols attributes for the textarea.</para>
        </section>

        <section id="views-form-macros-select">
          <title>Selection Fields</title>

          <para>Four selection field macros can be used to generate common UI
          value selection inputs in your HTML forms.</para>

          <itemizedlist>
            <listitem>
              <para>formSingleSelect</para>
            </listitem>

            <listitem>
              <para>formMultiSelect</para>
            </listitem>

            <listitem>
              <para>formRadioButtons</para>
            </listitem>

            <listitem>
              <para>formCheckboxes</para>
            </listitem>
          </itemizedlist>

          <para>Each of the four macros accepts a Map of options containing
          the value for the form field, and the label corresponding to that
          value. The value and the label can be the same.</para>

          <para>An example of radio buttons in FTL is below. The form backing
          object specifies a default value of 'London' for this field and so
          no validation is necessary. When the form is rendered, the entire
          list of cities to choose from is supplied as reference data in the
          model under the name 'cityMap'.</para>

          <programlisting>...
  Town:
  &lt;@spring.formRadioButtons "command.address.town", cityMap, "" /&gt;&lt;br&gt;&lt;br&gt;</programlisting>

          <para>This renders a line of radio buttons, one for each value in
          <literal>cityMap</literal> using the separator "". No additional
          attributes are supplied (the last parameter to the macro is
          missing). The cityMap uses the same String for each key-value pair
          in the map. The map's keys are what the form actually submits as
          POSTed request parameters, map values are the labels that the user
          sees. In the example above, given a list of three well known cities
          and a default value in the form backing object, the HTML would
          be</para>

          <programlisting>Town:
&lt;input type="radio" name="address.town" value="London"
   
&gt;
London
&lt;input type="radio" name="address.town" value="Paris"
  checked="checked" 
&gt;
Paris
&lt;input type="radio" name="address.town" value="New York"
   
&gt;
New York</programlisting>

          <para>If your application expects to handle cities by internal codes
          for example, the map of codes would be created with suitable keys
          like the example below.</para>

          <programlisting language="java">protected Map referenceData(HttpServletRequest request) throws Exception {
  Map cityMap = new LinkedHashMap();
  cityMap.put("LDN", "London");
  cityMap.put("PRS", "Paris");
  cityMap.put("NYC", "New York");
  
  Map m = new HashMap();
  m.put("cityMap", cityMap);
  return m;
}</programlisting>

          <para>The code would now produce output where the radio values are
          the relevant codes but the user still sees the more user friendly
          city names.</para>

          <programlisting>Town:
&lt;input type="radio" name="address.town" value="LDN"
   
&gt;
London
&lt;input type="radio" name="address.town" value="PRS"
  checked="checked" 
&gt;
Paris
&lt;input type="radio" name="address.town" value="NYC"
   
&gt;
New York</programlisting>
        </section>
      </section>

      <section id="views-form-macros-html-escaping">
        <title>HTML escaping and XHTML compliance</title>

        <para>Default usage of the form macros above will result in HTML tags
        that are HTML 4.01 compliant and that use the default value for HTML
        escaping defined in your web.xml as used by Spring's bind support. In
        order to make the tags XHTML compliant or to override the default HTML
        escaping value, you can specify two variables in your template (or in
        your model where they will be visible to your templates). The
        advantage of specifying them in the templates is that they can be
        changed to different values later in the template processing to
        provide different behavior for different fields in your form.</para>

        <para>To switch to XHTML compliance for your tags, specify a value of
        'true' for a model/context variable named xhtmlCompliant:</para>

        <programlisting>## for Velocity..
#set($springXhtmlCompliant = true)

&lt;#-- for FreeMarker --&gt;
&lt;#assign xhtmlCompliant = true in spring&gt;</programlisting>

        <para>Any tags generated by the Spring macros will now be XHTML
        compliant after processing this directive.</para>

        <para>In similar fashion, HTML escaping can be specified per
        field:</para>

        <programlisting language="xml">&lt;#-- until this point, default HTML escaping is used --&gt;

&lt;#assign htmlEscape = true in spring&gt;
&lt;#-- next field will use HTML escaping --&gt;
&lt;@spring.formInput "command.name" /&gt;

&lt;#assign htmlEscape = false in spring&gt;
&lt;#-- all future fields will be bound with HTML escaping off --&gt;</programlisting>
      </section>
    </section>
  </section>

  <section id="view-xslt">
    <title>XSLT</title>

    <para>XSLT is a transformation language for XML and is popular as a view
    technology within web applications. XSLT can be a good choice as a view
    technology if your application naturally deals with XML, or if your model
    can easily be converted to XML. The following section shows how to produce
    an XML document as model data and have it transformed with XSLT in a
    Spring Web MVC application.</para>

    <section id="view-xslt-firstwords">
      <title>My First Words</title>

      <para>This example is a trivial Spring application that creates a list
      of words in the <interfacename>Controller</interfacename> and adds them
      to the model map. The map is returned along with the view name of our
      XSLT view. See <xref linkend="mvc-controller" /> for details of Spring Web MVC's
      <interfacename>Controller</interfacename> interface. The XSLT view will
      turn the list of words into a simple XML document ready for
      transformation.</para>

      <section id="view-xslt-beandefs">
        <title>Bean definitions</title>

        <para>Configuration is standard for a simple Spring application. The
        dispatcher servlet config file contains a reference to a
        <interfacename>ViewResolver</interfacename>, URL mappings and a single
        controller bean...</para>

        <programlisting language="xml">&lt;bean id="homeController"class="xslt.HomeController"/&gt;</programlisting>

        <para>... that encapsulates our word generation logic.</para>
      </section>

      <section id="view-xslt-controllercode">
        <title>Standard MVC controller code</title>

        <para>The controller logic is encapsulated in a subclass of
        <classname>AbstractController</classname>, with the handler method
        being defined like so...</para>

        <programlisting language="java">protected ModelAndView handleRequestInternal(
    HttpServletRequest request,
    HttpServletResponse response) throws Exception {
        
    Map map = new HashMap();
    List wordList = new ArrayList();
        
    wordList.add("hello");
    wordList.add("world");
       
    map.put("wordList", wordList);
      
    return new ModelAndView("home", map);
}</programlisting>

        <para>So far we've done nothing that's XSLT specific. The model data
        has been created in the same way as you would for any other Spring MVC
        application. Depending on the configuration of the application now,
        that list of words could be rendered by JSP/JSTL by having them added
        as request attributes, or they could be handled by Velocity by adding
        the object to the <classname>VelocityContext</classname>. In order to
        have XSLT render them, they of course have to be converted into an XML
        document somehow. There are software packages available that will
        automatically 'domify' an object graph, but within Spring, you have
        complete flexibility to create the DOM from your model in any way you
        choose. This prevents the transformation of XML playing too great a
        part in the structure of your model data which is a danger when using
        tools to manage the domification process.</para>
      </section>

      <section id="view-xslt-subclassing">
        <title>Convert the model data to XML</title>

        <para>In order to create a DOM document from our list of words or any
        other model data, we must subclass the (provided)
        <classname>org.springframework.web.servlet.view.xslt.AbstractXsltView</classname>
        class. In doing so, we must also typically implement the abstract
        method <methodname>createXsltSource(..)</methodname> method. The first
        parameter passed to this method is our model map. Here's the complete
        listing of the <classname>HomePage</classname> class in our trivial
        word application:</para>

        <programlisting language="java">
package xslt;

<lineannotation>// imports omitted for brevity</lineannotation>

public class HomePage extends AbstractXsltView {

    protected Source createXsltSource(Map model, String rootName, HttpServletRequest
        request, HttpServletResponse response) throws Exception {

        Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
        Element root = document.createElement(rootName);

        List words = (List) model.get("wordList");
        for (Iterator it = words.iterator(); it.hasNext();) {
            String nextWord = (String) it.next();
            Element wordNode = document.createElement("word");
            Text textNode = document.createTextNode(nextWord);
            wordNode.appendChild(textNode);
            root.appendChild(wordNode);
        }
        return new DOMSource(root);
    }

}</programlisting>

        <para>A series of parameter name/value pairs can optionally be defined
        by your subclass which will be added to the transformation object. The
        parameter names must match those defined in your XSLT template
        declared with <literal>&lt;xsl:param
        name="myParam"&gt;defaultValue&lt;/xsl:param&gt;</literal>. To specify
        the parameters, override the <methodname>getParameters()</methodname>
        method of the <classname>AbstractXsltView</classname> class and return
        a <interfacename>Map</interfacename> of the name/value pairs. If your
        parameters need to derive information from the current request, you
        can override the <methodname>getParameters(HttpServletRequest
        request)</methodname> method instead.</para>
      </section>

      <section id="view-xslt-viewdefinitions">
        <title>Defining the view properties</title>

        <para>The views.properties file (or equivalent xml definition if
        you're using an XML based view resolver as we did in the Velocity
        examples above) looks like this for the one-view application that is
        'My First Words':</para>

        <programlisting>home.class=xslt.HomePage
home.stylesheetLocation=/WEB-INF/xsl/home.xslt
home.root=words</programlisting>

        <para>Here, you can see how the view is tied in with the
        <classname>HomePage</classname> class just written which handles the
        model domification in the first property <literal>'.class'</literal>.
        The <literal>'stylesheetLocation'</literal> property points to the
        XSLT file which will handle the XML transformation into HTML for us
        and the final property <literal>'.root'</literal> is the name that
        will be used as the root of the XML document. This gets passed to the
        <classname>HomePage</classname> class above in the second parameter to
        the <methodname>createXsltSource(..)</methodname> method(s).</para>
      </section>

      <section id="view-xslt-transforming">
        <title>Document transformation</title>

        <para>Finally, we have the XSLT code used for transforming the above
        document. As shown in the above
        <filename>'views.properties'</filename> file, the stylesheet is called
        <filename>'home.xslt'</filename> and it lives in the war file in the
        <filename class="directory">'WEB-INF/xsl'</filename> directory.</para>

        <programlisting language="xml">&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"&gt;

    &lt;xsl:output method="html" omit-xml-declaration="yes"/&gt;

    &lt;xsl:template match="/"&gt;
        &lt;html&gt;
            &lt;head&gt;&lt;title&gt;Hello!&lt;/title&gt;&lt;/head&gt;
            &lt;body&gt;
                &lt;h1&gt;My First Words&lt;/h1&gt;
                &lt;xsl:apply-templates/&gt;
            &lt;/body&gt;
        &lt;/html&gt;
    &lt;/xsl:template&gt;

    &lt;xsl:template match="word"&gt;
        &lt;xsl:value-of select="."/&gt;&lt;br/&gt;
    &lt;/xsl:template&gt;

&lt;/xsl:stylesheet&gt;</programlisting>
      </section>
    </section>

    <section id="view-xslt-summary">
      <title>Summary</title>

      <para>A summary of the files discussed and their location in the WAR
      file is shown in the simplified WAR structure below.</para>

      <programlisting>ProjectRoot
  |
  +- WebContent
      |
      +- WEB-INF
          |
          +- classes
          |    |
          |    +- xslt
          |    |   |
          |    |   +- HomePageController.class 
          |    |   +- HomePage.class
          |    |
          |    +- views.properties
          |
          +- lib
          |   |
          |   +- spring.jar
          |
          +- xsl
          |   |
          |   +- home.xslt
          |
          +- frontcontroller-servlet.xml</programlisting>

      <para>You will also need to ensure that an XML parser and an XSLT engine
      are available on the classpath. JDK 1.4 provides them by default, and
      most Java EE containers will also make them available by default, but it's
      a possible source of errors to be aware of.</para>
    </section>
  </section>

  <section id="view-document">
    <title>Document views (PDF/Excel)</title>

    <section id="view-document-intro">
      <title>Introduction</title>

      <para>Returning an HTML page isn't always the best way for the user to
      view the model output, and Spring makes it simple to generate a PDF
      document or an Excel spreadsheet dynamically from the model data. The
      document is the view and will be streamed from the server with the
      correct content type to (hopefully) enable the client PC to run their
      spreadsheet or PDF viewer application in response.</para>

      <para>In order to use Excel views, you need to add the 'poi' library to
      your classpath, and for PDF generation, the iText.jar. Both are included
      in the main Spring distribution.</para>
    </section>

    <section id="view-document-config">
      <title>Configuration and setup</title>

      <para>Document based views are handled in an almost identical fashion to
      XSLT views, and the following sections build upon the previous one by
      demonstrating how the same controller used in the XSLT example is
      invoked to render the same model as both a PDF document and an Excel
      spreadsheet (which can also be viewed or manipulated in Open
      Office).</para>

      <section id="view-document-configviews">
        <title>Document view definitions</title>

        <para>Firstly, let's amend the views.properties file (or xml
        equivalent) and add a simple view definition for both document types.
        The entire file now looks like this with the XSLT view shown from
        earlier.. <programlisting>home.class=xslt.HomePage
home.stylesheetLocation=/WEB-INF/xsl/home.xslt
home.root=words

xl.class=excel.HomePage

pdf.class=pdf.HomePage</programlisting> <emphasis>If you want to start with a
        template spreadsheet to add your model data to, specify the location
        as the 'url' property in the view definition</emphasis></para>
      </section>

      <section id="view-document-configcontroller">
        <title>Controller code</title>

        <para>The controller code we'll use remains exactly the same from the
        XSLT example earlier other than to change the name of the view to use.
        Of course, you could be clever and have this selected based on a URL
        parameter or some other logic - proof that Spring really is very good
        at decoupling the views from the controllers!</para>
      </section>

      <section id="view-document-configsubclasses">
        <title>Subclassing for Excel views</title>

        <para>Exactly as we did for the XSLT example, we'll subclass suitable
        abstract classes in order to implement custom behavior in generating
        our output documents. For Excel, this involves writing a subclass of
        <literal>org.springframework.web.servlet.view.document.AbstractExcelView</literal>
        (for Excel files generated by POI) or
        <literal>org.springframework.web.servlet.view.document.AbstractJExcelView</literal>
        (for JExcelApi-generated Excel files). and implementing the
        <literal>buildExcelDocument</literal></para>

        <para>Here's the complete listing for our POI Excel view which
        displays the word list from the model map in consecutive rows of the
        first column of a new spreadsheet.. <programlisting language="java">package excel;

// imports omitted for brevity

public class HomePage extends AbstractExcelView {

    protected void buildExcelDocument(
        Map model,
        HSSFWorkbook wb,
        HttpServletRequest req,
        HttpServletResponse resp)
        throws Exception {
    
        HSSFSheet sheet;
        HSSFRow sheetRow;
        HSSFCell cell;

        // Go to the first sheet
        // getSheetAt: only if wb is created from an existing document
        //sheet = wb.getSheetAt( 0 );
        sheet = wb.createSheet("Spring");
        sheet.setDefaultColumnWidth((short)12);

        // write a text at A1
        cell = getCell( sheet, 0, 0 );
        setText(cell,"Spring-Excel test");

        List words = (List ) model.get("wordList");
        for (int i=0; i &lt; words.size(); i++) {
            cell = getCell( sheet, 2+i, 0 );
            setText(cell, (String) words.get(i));

        }
    }
}</programlisting></para>

        <para>And this a view generating the same Excel file, now using
        JExcelApi: <programlisting language="java">package excel;
			
// imports omitted for brevity

public class HomePage extends AbstractExcelView {

    protected void buildExcelDocument(Map model,
        WritableWorkbook wb,
        HttpServletRequest request,
        HttpServletResponse response)
    throws Exception {
			
        WritableSheet sheet = wb.createSheet("Spring");

        sheet.addCell(new Label(0, 0, "Spring-Excel test");
		
        List words  = (List)model.get("wordList");
        for (int i = -; i &lt; words.size(); i++) {
            sheet.addCell(new Label(2+i, 0, (String)words.get(i));
        }
    }
}
</programlisting></para>

        <para>Note the differences between the APIs. We've found that the
        JExcelApi is somewhat more intuitive and furthermore, JExcelApi has a
        bit better image-handling capabilities. There have been memory
        problems with large Excel file when using JExcelApi however.</para>

        <para>If you now amend the controller such that it returns
        <literal>xl</literal> as the name of the view (<literal>return new
        ModelAndView("xl", map);</literal>) and run your application again,
        you should find that the Excel spreadsheet is created and downloaded
        automatically when you request the same page as before.</para>
      </section>

      <section id="view-document-configsubclasspdf">
        <title>Subclassing for PDF views</title>

        <para>The PDF version of the word list is even simpler. This time, the
        class extends
        <literal>org.springframework.web.servlet.view.document.AbstractPdfView</literal>
        and implements the <literal>buildPdfDocument()</literal> method as
        follows.. <programlisting language="java">package pdf;

// imports omitted for brevity

public class PDFPage extends AbstractPdfView {

    protected void buildPdfDocument(
        Map model,
        Document doc,
        PdfWriter writer,
        HttpServletRequest req,
        HttpServletResponse resp)
        throws Exception {
        
        List words = (List) model.get("wordList");
        
        for (int i=0; i&lt;words.size(); i++)
            doc.add( new Paragraph((String) words.get(i)));
    
    }
}</programlisting> Once again, amend the controller to return the
        <literal>pdf</literal> view with a <literal>return new
        ModelAndView("pdf", map);</literal> and reload the URL in your
        application. This time a PDF document should appear listing each of
        the words in the model map.</para>
      </section>
    </section>
  </section>

  <section id="view-jasper-reports">
    <title>JasperReports</title>

    <para>JasperReports (<ulink
    url="http://jasperreports.sourceforge.net"></ulink>) is a powerful
    open-source reporting engine that supports the creation of report designs
    using an easily understood XML file format. JasperReports is capable of
    rendering reports output into four different formats: CSV, Excel, HTML and
    PDF.</para>

    <section id="view-jasper-reports-dependencies">
      <title>Dependencies</title>

      <para>Your application will need to include the latest release of
      JasperReports, which at the time of writing was 0.6.1. JasperReports
      itself depends on the following projects:</para>

      <itemizedlist mark="bullet">
        <listitem>
          <para>BeanShell</para>
        </listitem>

        <listitem>
          <para>Commons BeanUtils</para>
        </listitem>

        <listitem>
          <para>Commons Collections</para>
        </listitem>

        <listitem>
          <para>Commons Digester</para>
        </listitem>

        <listitem>
          <para>Commons Logging</para>
        </listitem>

        <listitem>
          <para>iText</para>
        </listitem>

        <listitem>
          <para>POI</para>
        </listitem>
      </itemizedlist>

      <para>JasperReports also requires a JAXP compliant XML parser.</para>
    </section>

    <section id="view-jasper-reports-configuration">
      <title>Configuration</title>

      <para>To configure JasperReports views in your Spring container
      configuration you need to define a
      <interfacename>ViewResolver</interfacename> to map view names to the
      appropriate view class depending on which format you want your report
      rendered in.</para>

      <section id="view-jasper-reports-configuration-resolver">
        <title>Configuring the
        <interfacename>ViewResolver</interfacename></title>

        <para>Typically, you will use the
        <classname>ResourceBundleViewResolver</classname> to map view names to
        view classes and files in a properties file.</para>

        <programlisting language="xml">&lt;bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"&gt;
    &lt;property name="basename" value="views"/&gt;
&lt;/bean&gt;</programlisting>

        <para>Here we've configured an instance of the
        <classname>ResourceBundleViewResolver</classname> class that will look
        for view mappings in the resource bundle with base name
        <literal>views</literal>. (The content of this file is described in
        the next section.)</para>
      </section>

      <section id="view-jasper-reports-configuration-views">
        <title>Configuring the <literal>View</literal>s</title>

        <para>The Spring Framework contains five different
        <interfacename>View</interfacename> implementations for JasperReports,
        four of which correspond to one of the four output formats supported
        by JasperReports, and one that allows for the format to be determined
        at runtime:</para>

        <table id="view-jasper-reports-configuration-views-classes">
          <title>JasperReports <interfacename>View</interfacename>
          classes</title>

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

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

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

                <entry>Render Format</entry>
              </row>
            </thead>

            <tbody>
              <row>
                <entry><classname>JasperReportsCsvView</classname></entry>

                <entry>CSV</entry>
              </row>

              <row>
                <entry><classname>JasperReportsHtmlView</classname></entry>

                <entry>HTML</entry>
              </row>

              <row>
                <entry><classname>JasperReportsPdfView</classname></entry>

                <entry>PDF</entry>
              </row>

              <row>
                <entry><classname>JasperReportsXlsView</classname></entry>

                <entry>Microsoft Excel</entry>
              </row>

              <row>
                <entry><classname>JasperReportsMultiFormatView</classname></entry>

                <entry>The view is <link
                linkend="view-jasper-reports-configuration-multiformat-view">decided
                upon at runtime</link></entry>
              </row>
            </tbody>
          </tgroup>
        </table>

        <para>Mapping one of these classes to a view name and a report file is
        a matter of adding the appropriate entries into the resource bundle
        configured in the previous section as shown here:</para>

        <programlisting>simpleReport.class=org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView
simpleReport.url=/WEB-INF/reports/DataSourceReport.jasper</programlisting>

        <para>Here you can see that the view with name
        <literal>simpleReport</literal> is mapped to the
        <classname>JasperReportsPdfView</classname> class, causing the output
        of this report to be rendered in PDF format. The
        <literal>url</literal> property of the view is set to the location of
        the underlying report file.</para>
      </section>

      <section id="view-jasper-reports-configuration-report-files">
        <title>About Report Files</title>

        <para>JasperReports has two distinct types of report file: the design
        file, which has a <literal>.jrxml</literal> extension, and the
        compiled report file, which has a <literal>.jasper</literal>
        extension. Typically, you use the JasperReports Ant task to compile
        your <literal>.jrxml</literal> design file into a
        <literal>.jasper</literal> file before deploying it into your
        application. With the Spring Framework you can map either of these
        files to your report file and the framework will take care of
        compiling the <literal>.jrxml</literal> file on the fly for you. You
        should note that after a <literal>.jrxml</literal> file is compiled by
        the Spring Framework, the compiled report is cached for the lifetime
        of the application. To make changes to the file you will need to
        restart your application.</para>
      </section>

      <section id="view-jasper-reports-configuration-multiformat-view">
        <title>Using
        <classname>JasperReportsMultiFormatView</classname></title>

        <para>The <classname>JasperReportsMultiFormatView</classname> allows
        for report format to be specified at runtime. The actual rendering of
        the report is delegated to one of the other JasperReports view classes
        - the <classname>JasperReportsMultiFormatView</classname> class simply
        adds a wrapper layer that allows for the exact implementation to be
        specified at runtime.</para>

        <para>The <classname>JasperReportsMultiFormatView</classname> class
        introduces two concepts: the format key and the discriminator key. The
        <classname>JasperReportsMultiFormatView</classname> class uses the
        mapping key to lookup the actual view implementation class and uses
        the format key to lookup up the mapping key. From a coding perspective
        you add an entry to your model with the formay key as the key and the
        mapping key as the value, for example:</para>

        <programlisting language="java">public ModelAndView handleSimpleReportMulti(HttpServletRequest request,
HttpServletResponse response) throws Exception {

  String uri = request.getRequestURI();
  String format = uri.substring(uri.lastIndexOf(".") + 1);

  Map model = getModel();
  model.put("format", format);

  return new ModelAndView("simpleReportMulti", model);
}</programlisting>

        <para>In this example, the mapping key is determined from the
        extension of the request URI and is added to the model under the
        default format key: <literal>format</literal>. If you wish to use a
        different format key then you can configure this using the
        <literal>formatKey</literal> property of the
        <classname>JasperReportsMultiFormatView</classname> class.</para>

        <para>By default the following mapping key mappings are configured in
        <classname>JasperReportsMultiFormatView</classname>:</para>

        <table id="view-jasper-reports-configuration-multiformat-view-mappings">
          <title><classname>JasperReportsMultiFormatView</classname> Default
          Mapping Key Mappings</title>

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

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

            <thead>
              <row>
                <entry>Mapping Key</entry>

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

            <tbody>
              <row>
                <entry>csv</entry>

                <entry><classname>JasperReportsCsvView</classname></entry>
              </row>

              <row>
                <entry>html</entry>

                <entry><classname>JasperReportsHtmlView</classname></entry>
              </row>

              <row>
                <entry>pdf</entry>

                <entry><classname>JasperReportsPdfView</classname></entry>
              </row>

              <row>
                <entry>xls</entry>

                <entry><classname>JasperReportsXlsView</classname></entry>
              </row>
            </tbody>
          </tgroup>
        </table>

        <para>So in the example above a request to URI /foo/myReport.pdf would
        be mapped to the <literal>JasperReportsPdfView</literal> class. You
        can override the mapping key to view class mappings using the
        <literal>formatMappings</literal> property of
        <classname>JasperReportsMultiFormatView</classname>.</para>
      </section>
    </section>

    <section id="view-jasper-reports-model">
      <title>Populating the <classname>ModelAndView</classname></title>

      <para>In order to render your report correctly in the format you have
      chosen, you must supply Spring with all of the data needed to populate
      your report. For JasperReports this means you must pass in all report
      parameters along with the report datasource. Report parameters are
      simple name/value pairs and can be added be to the
      <interfacename>Map</interfacename> for your model as you would add any
      name/value pair.</para>

      <para>When adding the datasource to the model you have two approaches to
      choose from. The first approach is to add an instance of
      <classname>JRDataSource</classname> or a
      <interfacename>Collection</interfacename> type to the model
      <interfacename>Map</interfacename> under any arbitrary key. Spring will
      then locate this object in the model and treat it as the report
      datasource. For example, you may populate your model like so:</para>

      <programlisting language="java">private Map getModel() {
  Map model = new HashMap();
  Collection beanData = getBeanData();
  model.put("myBeanData", beanData);
  return model;
}</programlisting>

      <para>The second approach is to add the instance of
      <literal>JRDataSource</literal> or <literal>Collection</literal> under a
      specific key and then configure this key using the
      <literal>reportDataKey</literal> property of the view class. In both
      cases Spring will instances of <literal>Collection</literal> in a
      <literal>JRBeanCollectionDataSource</literal> instance. For
      example:</para>

      <programlisting language="java">private Map getModel() {
  Map model = new HashMap();
  Collection beanData = getBeanData();
  Collection someData = getSomeData();
  model.put("myBeanData", beanData);
  model.put("someData", someData);
  return model;
}</programlisting>

      <para>Here you can see that two <literal>Collection</literal> instances
      are being added to the model. To ensure that the correct one is used, we
      simply modify our view configuration as appropriate:</para>

      <programlisting>simpleReport.class=org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView
simpleReport.url=/WEB-INF/reports/DataSourceReport.jasper
simpleReport.reportDataKey=myBeanData</programlisting>

      <para>Be aware that when using the first approach, Spring will use the
      first instance of <literal>JRDataSource</literal> or
      <literal>Collection</literal> that it encounters. If you need to place
      multiple instances of <literal>JRDataSource</literal> or
      <literal>Collection</literal> into the model then you need to use the
      second approach.</para>
    </section>

    <section id="view-jasper-reports-subreports">
      <title>Working with Sub-Reports</title>

      <para>JasperReports provides support for embedded sub-reports within
      your master report files. There are a wide variety of mechanisms for
      including sub-reports in your report files. The easiest way is to hard
      code the report path and the SQL query for the sub report into your
      design files. The drawback of this approach is obvious - the values are
      hard-coded into your report files reducing reusability and making it
      harder to modify and update report designs. To overcome this you can
      configure sub-reports declaratively and you can include additional data
      for these sub-reports directly from your controllers.</para>

      <section id="view-jasper-reports-subreports-config-reports">
        <title>Configuring Sub-Report Files</title>

        <para>To control which sub-report files are included in a master
        report using Spring, your report file must be configured to accept
        sub-reports from an external source. To do this you declare a
        parameter in your report file like so:</para>

        <programlisting language="xml">&lt;parameter name="ProductsSubReport" class="net.sf.jasperreports.engine.JasperReport"/&gt;</programlisting>

        <para>Then, you define your sub-report to use this sub-report
        parameter:</para>

        <programlisting language="xml">&lt;subreport&gt;
    &lt;reportElement isPrintRepeatedValues="false" x="5" y="25" width="325"
        height="20" isRemoveLineWhenBlank="true" backcolor="#ffcc99"/&gt;
    &lt;subreportParameter name="City"&gt;
        &lt;subreportParameterExpression&gt;&lt;![CDATA[$F{city}]]&gt;&lt;/subreportParameterExpression&gt;
    &lt;/subreportParameter&gt;
    &lt;dataSourceExpression&gt;&lt;![CDATA[$P{SubReportData}]]&gt;&lt;/dataSourceExpression&gt;
    &lt;subreportExpression class="net.sf.jasperreports.engine.JasperReport"&gt;
                  &lt;![CDATA[$P{ProductsSubReport}]]&gt;&lt;/subreportExpression&gt;
&lt;/subreport&gt;</programlisting>

        <para>This defines a master report file that expects the sub-report to
        be passed in as an instance of
        <literal>net.sf.jasperreports.engine.JasperReports</literal> under the
        parameter <literal>ProductsSubReport</literal>. When configuring your
        Jasper view class, you can instruct Spring to load a report file and
        pass into the JasperReports engine as a sub-report using the
        <literal>subReportUrls</literal> property:</para>

        <programlisting language="xml">&lt;property name="subReportUrls"&gt;
    &lt;map&gt;
        &lt;entry key="ProductsSubReport" value="/WEB-INF/reports/subReportChild.jrxml"/&gt;
    &lt;/map&gt;
&lt;/property&gt;</programlisting>

        <para>Here, the key of the <interfacename>Map</interfacename>
        corresponds to the name of the sub-report parameter in th report
        design file, and the entry is the URL of the report file. Spring will
        load this report file, compiling it if necessary, and will pass into
        the JasperReports engine under the given key.</para>
      </section>

      <section id="view-jasper-reports-subreports-config-datasources">
        <title>Configuring Sub-Report Data Sources</title>

        <para>This step is entirely optional when using Spring configure your
        sub-reports. If you wish, you can still configure the data source for
        your sub-reports using static queries. However, if you want Spring to
        convert data returned in your <literal>ModelAndView</literal> into
        instances of <literal>JRDataSource</literal> then you need to specify
        which of the parameters in your <literal>ModelAndView</literal> Spring
        should convert. To do this configure the list of parameter names using
        the <literal>subReportDataKeys</literal> property of the your chosen
        view class: <programlisting language="xml">&lt;property name="subReportDataKeys"
    value="SubReportData"/&gt;</programlisting> Here, the key you supply MUST
        correspond to both the key used in your
        <literal>ModelAndView</literal> and the key used in your report design
        file.</para>
      </section>
    </section>

    <section id="view-jasper-reports-exporter-parameters">
      <title>Configuring Exporter Parameters</title>

      <para>If you have special requirements for exporter configuration -
      perhaps you want a specific page size for your PDF report, then you can
      configure these exporter parameters declaratively in your Spring
      configuration file using the <literal>exporterParameters</literal>
      property of the view class. The <literal>exporterParameters</literal>
      property is typed as <interfacename>Map</interfacename> and in your
      configuration the key of an entry should be the fully-qualified name of
      a static field that contains the exporter parameter definition and the
      value of an entry should be the value you want to assign to the
      parameter. An example of this is shown below:</para>

      <programlisting language="xml">&lt;bean id="htmlReport" class="org.springframework.web.servlet.view.jasperreports.JasperReportsHtmlView"&gt;
  &lt;property name="url" value="/WEB-INF/reports/simpleReport.jrxml"/&gt;
  &lt;property name="exporterParameters"&gt;
    &lt;map&gt;
      &lt;entry key="net.sf.jasperreports.engine.export.JRHtmlExporterParameter.HTML_FOOTER"&gt;
        &lt;value&gt;Footer by Spring!
          &amp;lt;/td&amp;gt;&amp;lt;td width="50%"&amp;gt;&amp;amp;nbsp; &amp;lt;/td&amp;gt;&amp;lt;/tr&amp;gt;
          &amp;lt;/table&amp;gt;&amp;lt;/body&amp;gt;&amp;lt;/html&amp;gt;
        &lt;/value&gt;
      &lt;/entry&gt;
    &lt;/map&gt;
  &lt;/property&gt;
&lt;/bean&gt;</programlisting>

      <para>Here you can see that the
      <classname>JasperReportsHtmlView</classname> is being configured with an
      exporter parameter for
      <literal>net.sf.jasperreports.engine.export.JRHtmlExporterParameter.HTML_FOOTER</literal>
      which will output a footer in the resulting HTML.</para>
    </section>
  </section>

  <section id="view-feeds">
    <title>Feed Views</title>

    <para>Both <classname>AbstractAtomFeedView</classname> and
    <classname>AbstractRssFeedView</classname> inherit from the base class
    <classname>AbstractFeedView</classname> and are used to provide Atom and
    RSS Feed views respectfully. They are based on java.net's <ulink
    url="https://rome.dev.java.net">ROME</ulink> project and are located in
    the package
    <literal>org.springframework.web.servlet.view.feed</literal>.</para>

    <para><classname>AbstractAtomFeedView</classname> requires you to
    implement the <methodname>buildFeedEntries</methodname> method and
    optionally override the <methodname>buildFeedMetadata</methodname> method
    (the default implementation is empty), as shown below</para>

    <programlisting language="java">public class SampleContentAtomView extends AbstractAtomFeedView {

  @Override
  protected void buildFeedMetadata(Map&lt;String, Object&gt; model, Feed feed,
                                   HttpServletRequest request) {
      // implementation omitted
  }

  @Override
  protected List&lt;Entry&gt; buildFeedEntries(Map&lt;String, Object&gt; model,
                                         HttpServletRequest request,
                                         HttpServletResponse response) throws Exception {

      // implementation omitted
  }
}</programlisting>

    <para>Similar requirements apply for implementing
    <classname>AbstractRssFeedView</classname>, as shown below</para>

    <programlisting language="java">public class SampleContentAtomView extends AbstractRssFeedView {

  @Override
  protected void buildFeedMetadata(Map&lt;String, Object&gt; model, Channel feed,
                                   HttpServletRequest request) {
    // implementation omitted
  }

  @Override
  protected List&lt;Item&gt; buildFeedItems(Map&lt;String, Object&gt; model,
                                      HttpServletRequest request,
                                      HttpServletResponse response) throws Exception {
    // implementation omitted
  }

}</programlisting>

    <para>The <methodname>buildFeedItems</methodname> and
    <methodname>buildFeedEntires</methodname> pass in the HTTP request in case
    you need to access the Locale. The HTTP response is passed in only for the
    setting of cookies or other HTTP headers. The feed will automatically be
    written to the response object after the method returns.</para>

    <para>For an example of creating a Atom view please refer to Alef
    Arendsen's SpringSource TeamBlog <ulink
    url="http://blog.springsource.com/2009/03/16/adding-an-atom-view-to-an-application-using-springs-rest-support/">entry</ulink>.</para>
  </section>

  <section>
    <title>XML Marshalling View</title>

    <para>The <classname>MarhsallingView</classname> uses a XML
    <interfacename>Marshaller</interfacename> defined in the
    <classname>org.springframework.oxm</classname> package to render the
    response content as XML. The object to be marshalled can be set explicitly
    using <classname>MarhsallingView</classname>'s
    <property>modelKey</property> bean property. Alternatively, the view will
    iterate over all model properties marhsall only those types that are
    supported by the <interfacename>Marshaller</interfacename>. For more
    information on the functionality in the
    <classname>org.springframework.oxm</classname> package refer to the
    chapter <link linkend="oxm">Marshalling XML using O/X
    Mappers</link>.</para>
  </section>
</chapter>
