Inheritance

Since our previous definition is abstract, we need to extend it to get a concrete panel definition:

<panel name="/base.page" template="/WEB-INF/jsp/layout/page.jsp">
  <panel name="header" template="/WEB-INF/jsp/layout/header.jsp"/>
  <panel name="menu" template="/WEB-INF/jsp/layout/menu.jsp"/>
  <panel name="content"/>
  <panel name="footer" template="/WEB-INF/jsp/layout/footer.jsp"/>
</panel>

<panel name="/derived.page" super="/base.page">
  <panel name="content" template="/WEB-INF/jsp/content/foo.jsp"/>
</panel>

The super attribute is used to specify a toplevel panel as a base panel definition. In the above example, the /derived.page panel associates a template with the content subpanel, making it concrete.

Let us examine a slightly more complex example:

<panel name="/base">
  <panel name="nested">
    <param name="param1" value="p1"/>
    <param name="param2" value="p2"/>
    <panel name="nested1nested"/>
  </param>
</panel>

<panel name="/derived" super="/base" template="/WEB-INF/derived.jsp">
  <panel name="nested" template="/WEB-INF/nested1.jsp">
    <param name="param1" value="p1"/>
    <param name="param2" value="override p2"/>
    <param name="param3" value="add p3"/>
  </param>
  <panel name="nested2" template="/WEB-INF/nested2.jsp"/>
</panel>

<panel name="/concrete" template="/WEB-INF/derived2.jsp">
  <panel name="foo" super="/derived">
    <panel name="nested">
      <panel name="nested1nested" template="/WEB-INF/bar.jsp"/>
      <param name="param3" value="override p3"/>
    </panel>
  </panel>
</panel>

Don't run away! It looks harder than it is... Let's work out what happens here:

• Toplevel panel /base defines an abstract subpanel nested. It is abstract, because it does not specify a template attribute and also, because it has an abstract subpanel nested1nested.
• Panel /derived extends /base and assigns a template value to nested, assigns a value to nested's param1, overrides the param2 parameter and adds the param3 parameter. Finally, it adds nested2, another nested panel. However, /derived is still abstract, because it inherits the abstract nested1nested panel.
• The /concrete panel definition takes a foo subpanel, which is derived from /derived. The foo panel overrides param3. Since it assigns a template attribute to nested1nested, foo is concrete and thus /concrete is concrete.

Got it?