8.3. Starting conversations with GET requests
JSF does not define any action listener triggered when a page is accessed via a non-Faces request (a HTTP GET request, for example). This can occur when a user bookmarks the page, or navigates to the page via an
<h:outputLink>.
Sometimes we want a conversation to begin immediately the page is accessed. Since there is no JSF action method, we cannot annotate the action with
@Begin.
Further problems arise when the page requires state to be fetched into a context variable. We have already seen two methods of solving this problem. If the state is held in a Seam component, we can fetch the state in a
@Create method. If not, we can define a @Factory method for the context variable.
If neither option works for you, Seam lets you define a page action in the
pages.xml file.
<pages>
<page view-id="/messageList.jsp" action="#{messageManager.list}"/>
...
</pages>
This action method is called at the beginning of the render response phase — that is, any time the page is about to be rendered. If a page action returns a non-null outcome, Seam will process any appropriate JSF and Seam navigation rules. This can result in a completely different page rendering.
If beginning a conversation is all you want to do before rendering the page, you can use a built-in action method:
<pages>
<page view-id="/messageList.jsp" action="#{conversation.begin}"/>
...
</pages>
You can also call this built-in action from a JSF control, and that
#{conversation.end} similarly ends conversations.
The
<begin-conversation> element can be used as follows for further control over joining existing conversations, or beginning a nested converstion, a pageflow, or an atomic conversation.
<pages>
<page view-id="/messageList.jsp">
<begin-conversation nested="true" pageflow="AddItem"/>
<page>
...
</pages>
There is also an
<end-conversation> element.
<pages>
<page view-id="/home.jsp">
<end-conversation/>
<page>
...
</pages>
We now have five options to begin a conversation immediately the page is accessed:
- Annotate the
@Createmethod with@Begin - Annotate the
@Factorymethod with@Begin - Annotate the Seam page action method with
@Begin - Use
<begin-conversation>inpages.xml. - Use
#{conversation.begin}as the Seam page action method
