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         -----------
         Expression Language (EL) support
         -----------

Expression Language (EL) support

  With Tiles it is possible to use EL not only in JSP pages, but also in XML
  definition files.

* Configuration

  To enable EL support in XML definition files, you have to configure the class of the
  {{{../../apidocs/org/apache/tiles/evaluator/AttributeEvaluator.html} AttributeEvaluator}}.

  If you are using declarative configuration in <<<web.xml>>> file, you have to use the
  {{{../../config-reference.html#org.apache.tiles.evaluator.AttributeEvaluator} org.apache.tiles.evaluator.AttributeEvaluator}}
  parameter. In the case of <<<TilesServlet>>>:

------------------------------------
<servlet>
    <servlet-name>tiles-init</servlet-name>
    <servlet-class>org.apache.tiles.web.startup.TilesServlet</servlet-class>
    <init-param>
        <param-name>org.apache.tiles.evaluator.AttributeEvaluator</param-name>
        <param-value>org.apache.tiles.evaluator.el.ELAttributeEvaluatr</param-value>
    </init-param>
</servlet>
------------------------------------

  If you are using programmatic configuration via Java, override the
  {{{../../apidocs/org/apache/tiles/factory/BasicTilesContainerFactory.html#createEvaluator(java.lang.Object,%20org.apache.tiles.TilesApplicationContext,%20org.apache.tiles.context.TilesRequestContextFactory,%20org.apache.tiles.locale.LocaleResolver)} createEvaluator}}
  method, providing <<only the creation>> of the instance of the
  <<<AttributeEvaluator>>>.
  
  If you are using Servlet 2.5 or above, you can leverage your container EL support.

------------------------------------
    /** {@inheritDoc} */
    @Override
    protected AttributeEvaluator createEvaluator(Object context,
            TilesApplicationContext applicationContext,
            TilesRequestContextFactory contextFactory, LocaleResolver resolver) {
        ELAttributeEvaluator evaluator = new ELAttributeEvaluator();
        evaluator.setApplicationContext(applicationContext);
        MultiversionExpressionFactoryFactory efFactory = new JspExpressionFactoryFactory();
        efFactory.setApplicationContext(applicationContext);
        evaluator.setExpressionFactory(efFactory.getExpressionFactory());
        ELResolver elResolver = new CompositeELResolver() {
            {
                add(new TilesContextELResolver());
                add(new TilesContextBeanELResolver());
                add(new ArrayELResolver(false));
                add(new ListELResolver(false));
                add(new MapELResolver(false));
                add(new ResourceBundleELResolver());
            }
        };
        evaluator.setResolver(elResolver);

        return evaluator;
    }
------------------------------------

  If you are using Servlet 2.4, you still can use Tiles EL support but:
  
  * You have to put <<<jasper-el-6.0.16.jar>>> (or newer version) in your classpath.

  * Use <<<TomcatExpressionFactoryFactory>>> instead of
  <<<JspExpressionFactoryFactory>>>.

* Usage

  Let's use this example:
  
------------------------------------
  <definition name="test.composite.el.definition" templateExpression="${layout}"
        preparer="org.apache.tiles.test.preparer.RequestSettingViewPreparer">
      <put-attribute name="title"  value="This is a configured composite definition."/>
      <put-attribute name="header" value="/header.jsp"/>
      <put-attribute name="body"   expression="${requestScope.body}"/>
  </definition>
------------------------------------

  Before rendering the definition:
 
  * The template name will be taken from the "layout" attribute, searched in every scope.

  * The body will be taken from the "body" attribute in request scope.