Java Doc for Interceptor.java in  » J2EE » webwork-2.2.6 » com » opensymphony » xwork » interceptor » Java Source Code / Java DocumentationJava Source Code and Java Documentation

Interceptors are objects that dynamically intercept Action invocations. They provide the developer with the opportunity to define code that can be executed before and/or after the execution of an action. They also have the ability to prevent an action from executing. Interceptors provide developers a way to encapulate common functionality in a re-usable form that can be applied to one or more Actions.

Interceptors must be stateless and not assume that a new instance will be created for each request or Action. Interceptors may choose to either short-circuit the ActionInvocation execution and return a return code (such as com.opensymphony.xwork.Action.SUCCESS ), or it may choose to do some processing before and/or after delegating the rest of the procesing using ActionInvocation.invoke .

Interceptor's parameter could be overriden through the following ways :-

Method 1:

 <action name="myAction" class="myActionClass">
 <interceptor-ref name="exception"/>
 <interceptor-ref name="alias"/>
 <interceptor-ref name="params"/>
 <interceptor-ref name="servlet-config"/>
 <interceptor-ref name="prepare"/>
 <interceptor-ref name="i18n"/>
 <interceptor-ref name="chain"/>
 <interceptor-ref name="model-driven"/>
 <interceptor-ref name="fileUpload"/>
 <interceptor-ref name="static-params"/>
 <interceptor-ref name="params"/>
 <interceptor-ref name="conversionError"/>
 <interceptor-ref name="validation">
 <param name="excludeMethods">myValidationExcudeMethod</param>
 </interceptor-ref>
 <interceptor-ref name="workflow">
 <param name="excludeMethods">myWorkflowExcludeMethod</param>
 </interceptor-ref>
 </action>
 

 <action name="myAction" class="myActionClass">
 <interceptor-ref name="defaultStack">
 <param name="validation.excludeMethods">myValidationExcludeMethod</param>
 <param name="workflow.excludeMethods">myWorkflowExcludeMethod</param>
 </interceptor-ref>
 </action>
 

In the first method, the whole default stack is copied and the parameter then changed accordingly.

In the second method, the refer to an existing interceptor-stack, namely default-stack in this example, and override the validator and workflow interceptor excludeMethods typically in this case. Note that in the tag, the name attribute contains a dot (.) the word before the dot(.) specifies the interceptor name whose parameter is to be overriden and the word after the dot (.) specifies the parameter itself. Essetially it is as follows :-

 <interceptor-name>.<parameter-name>
 

 <interceptor name="interceptor1" class="foo.bar.Interceptor1" />
 <interceptor name="interceptor2" class="foo.bar.Interceptor2" />
 <interceptor name="interceptor3" class="foo.bar.Interceptor3" />
 <interceptor name="interceptor4" class="foo.bar.Interceptor4" />
 <interceptor-stack name="stack1">
 <interceptor-ref name="interceptor1" />
 </interceptor-stack>
 <interceptor-stack name="stack2">
 <interceptor-ref name="intercetor2" />
 <interceptor-ref name="stack1" />
 </interceptor-stack>
 <interceptor-stack name="stack3">
 <interceptor-ref name="interceptor3" />
 <interceptor-ref name="stack2" />
 </interceptor-stack>
 <interceptor-stack name="stack4">
 <interceptor-ref name="interceptor4" />
 <interceptor-ref name="stack3" />
 </interceptor-stack>
 

 <action ... >
 <!-- to override parameters of interceptor located directly in the stack  -->
 <interceptor-ref name="stack4">
 <param name="interceptor4.param4"> ... </param>
 </interceptor-ref>
 </action>
 <action ... >
 <!-- to override parameters of interceptor located under nested stack -->
 <interceptor-ref name="stack4">
 <param name="stack3.interceptor3.param3"> ... </param>
 <param name="stack3.stack2.interceptor2.param2"> ... </param>
 <param name="stack3.stack2.stack1.interceptor1.param1"> ... </param>
 </interceptor-ref>
 </action>