src/site/apt/tutorial/advanced/el-support.apt

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

Expression Language support

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

  Currently supported languages are Unified EL (as in javax.el), i.e. the language used in JSP code,
  {{{http://mvel.codehaus.org/}MVEL}} and {{{http://commons.apache.org/ognl/}OGNL}}.

* Configuration

  By default, Tiles does not use an expression language, attribute values are simply used as they are.
  
  <<<CompleteAutoloadTilesContainerFactory>>> enables support of Unified EL, MVEL and OGNL as follows:
  
  - an attribute expression starting with "MVEL:" or "OGNL:" is interpreted in one of those languages.
  - otherwise, the parts of the expression between the braces in <<<$\{...\}>>> are interpreted in Unified EL.  

* Unified EL support

  The EL language is supported since Tiles 2.1.

  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.

* {MVEL Support}

  Let's use this example:

------------------------------------
  <definition name="test.composite.mvel.definition" templateExpression="MVEL: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="MVEL: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.

* {OGNL Support}

  Let's use this example:

------------------------------------
  <definition name="test.composite.mvel.definition" templateExpression="OGNL: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="OGNL: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.