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7.2. Page actions

A Seam page action is an event occurring immediately before a JSF request is rendered. Declare page actions in WEB-INF/pages.xml. We can define a page action for a particular JSF view ID: 
<pages> 
    <page view-id="/hello.jsp" action="#{helloWorld.sayHello}"/> 
    </pages>
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Or we can use a * wildcard as a suffix to the view-id to specify an action that applies to all view IDs that match that pattern: 
<pages> 
    <page view-id="/hello/*" action="#{helloWorld.sayHello}"/> 
    </pages>
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Note

If the <page> element is defined in a fine-grained page descriptor, the view-id attribute can be omitted, as it is already implied.
If multiple wildcarded page actions match the current view-id, Seam will call all the actions, in order of least-specific to most-specific.
The page action method can return a JSF outcome. If the outcome is not null, Seam uses the defined navigation rules to navigate to a view.
The view ID mentioned in the <page> element need not correspond to a real JSP or Facelets page. This way, we can reproduce the functionality of a traditional action-oriented framework like Struts or WebWork using page actions. This is useful for performing complex actions in response to non-Faces requests like HTTP GET.
Multiple or conditional page actions can be specified with the <action> tag: 
<pages> 
  <page view-id="/hello.jsp">
    <action execute="#{helloWorld.sayHello}" 
            if="#{not validation.failed}"/>
    <action execute="#{hitCount.increment}"/> 
  </page> 
</pages>
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Page actions are executed on both an initial (non-Faces) request and a postback (Faces) request. If you use the page action to load data, it may conflict with the standard JSF actions being executed on a postback. One way to disable the page action is to set up a condition that resolves to true only upon an initial request. 
<pages> 
  <page view-id="/dashboard.xhtml"> 
    <action execute="#{dashboard.loadData}" 
            if="#{not FacesContext.renderKit.responseStateManager
                .isPostback(FacesContext)}"/> 
  </page> 
</pages>
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This condition consults the ResponseStateManager#isPostback(FacesContext) to determine if the request is a postback. The ResponseStateManager is accessed using FacesContext.getCurrentInstance().getRenderKit(). getResponseStateManager().
Seam offers a built-in condition that accomplishes this result less verbosely. You can disable a page action on a postback by setting the on-postback attribute to false: 
<pages> 
    <page view-id="/dashboard.xhtml"> 
    <action execute="#{dashboard.loadData}" on-postback="false"/> 
    </page> 
    </pages>
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The on-postback attribute defaults to true to maintain backwards compatibility. However, you are more likely to use false more often.
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