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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>
<pages>
<page view-id="/hello.jsp" action="#{helloWorld.sayHello}"/>
</pages>
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>
<pages>
<page view-id="/hello/*" action="#{helloWorld.sayHello}"/>
</pages>
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:
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.
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:
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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