src/site/apt/tutorial/advanced/preparer.apt

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         Tiles View Preparers
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View Preparers

  Sometimes a definition, before it is rendered, needs to be "prepared". For
  example when showing a menu, the menu structure must be created and stored
  in the request scope.

  For this reason, a <<View Preparer>> can be used: it is called <<before>> the
  definition is rendered, so all the things needed to render correctly the
  definition can be prepared.

* Creating a view preparer

  A View Preparer is simply a class that implement the <<<ViewPreparer>>>
  interface. The <<<execute>>> method allows to execute code <<before>> a
  definition is rendered. You can extend the <<<ViewPreparerSupport>>> class to
  avoid compiling problems in the case the <<<ViewPreparer>>> interface changes.

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package my.package;

import org.apache.tiles.preparer.PreparerException;
import org.apache.tiles.preparer.ViewPreparer;
import org.apache.tiles.request.Request;
import org.apache.tiles.AttributeContext;
import org.apache.tiles.Attribute;

public class TestViewPreparer implements ViewPreparer {

    public void execute(Request tilesRequest, AttributeContext attributeContext)
    throws PreparerException {
        attributeContext.putAttribute(
            "body",
            new Attribute("This is the value added by the ViewPreparer"));
    }
}
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* Associating a preparer

  To associate a preparer to a definition, put its complete path name to the
  <<<preparer>>> attribute of the <<<\<definition\>>>> element:

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<definition name="preparer.definition" preparer="org.apache.tiles.test.preparer.TestViewPreparer">
  <put-attribute name="foo" value="/bar/foo.jsp" />
</definition>
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