|Apache Struts 2 Documentation > Home > Guides > Plugin Developers Guide > Portlet Plugin|
|The Portlet Plugin is used for developing JSR168 portlets using Struts 2.|
To use the Struts 2 Portlet framework, use org.apache.struts2.portlet.dispatcher.Jsr168Dispatcher as the portlet class in your portlet.xml file:
Below is the init-param elements that you can set up in portlet.xml for configuring the portlet mode -> xwork namespace mappings for the portlet. Basically, you can think of the different portlet modes as different sub-applications, so it can be useful to set up the struts.xml configuration with different namespaces for the different portlets and modes:
|portletNamespace||The namespace for the portlet in the action configuration. This namespace is prepended to all action lookups, and makes it possible to host multiple portlets in the same portlet application. If this parameter is set, the complete namespace will be /portletNamespace/modeNamespace/actionName||The default namespace.|
|viewNamespace||The namespace in the xwork config for the view portlet mode.||The default namespace.|
|editNamespace||The namespace in the xwork config for the edit portlet mode.||The default namespace.|
|helpNamespace||The namespace in the xwork config for the help portlet mode.||The default namespace.|
|defaultViewAction||Name of the action to use as default for the view portlet mode, when no action name is present.||default|
|defaultEditAction||Name of the action to use as default for the edit portlet mode, when no action name is present.||default|
|defaultHelpAction||Name of the action to use as default for the help portlet mode, when no action name is present.||default|
This snippet from portlet.xml will set up the portlet with a namespace of /portletA/. This means that all requests to this portlet will get the namespace prepended when looking up the action. In addition, the _view portlet mode will map to the /view namespace, so a request for action myAction will resolve to the namespace and action /portletA/view/myAction. It also means that if no action is requested, the default action of index will be used for the request.
If you want to access to expose the value stack through request attributes (e.g. if you want to use regular JSTL tags to access values in the stack), you have to configure the dispatcher servlet in your web application descriptor:
|If you're only using Struts 2 tags, configuring the dispatcher servlet is optional|
The portlet specification describes that a portlet request cycle can consist of two phases, an event phase and a render phase. In case of an event in the portlet, it will always execute before the render phase. The event phase is typically for changing the state of the application. In a portlet, this is typically when a form is submitted. The render phase will then prepare and dispatch to the view. It's recommended that you set up the result from an action that is executed in the event phase to point to another action that is executed in the render phase, which again is responsible for dispatching to the actual view.
The struts-portlet-default package defines a special default Result Type, which is responsible for performing the result logic of an Action execution. Typically, this involves including a JSP for rendering, or preparing a render action if one is configured for the current event action.
This result type has three main modes of execution.
The action executed in event mode can pass render parameters to the next action to execute in render mode through parameters using the redirectAction result type:
This will set up a render parameter called userId with the value of the userId property on the value stack.
You can also use the portletMode parameter to change to a different portlet mode.
URLs in a portlet is handled quite different than for a regular web application. There's no such thing as "extension", there's simply an action name and a namespace, and they have to be specified using the respective tag attributes. URLs using the value attribute will be encoded as a resource URL and is only suitable for additional resources such as images and style sheets.
|<s:url value="hello.action"/>||<s:url action="hello"/>|
|<s:url value="style.css"/>||<s:url value="style.css"/>|
In addition, there are some additional tag attributes that are portlet specific. These are:
|portletMode||The resulting portlet mode of the url|
|windowState||The resulting window state of the url|
|portletUrlType||Specifies if this is a render or an action url|
Typical usage for the portletUrlType is if you have a delete link that removes something from a database. To ensure this is done in the event phase, as recommended by the portlet specification (since it is a change of state), the url can use this attribute, e.g. <s:url action="deleteEntry" portletUrlType="action"/>