An interceptor is a stateless class that follows the interceptor pattern, as found in {@link javax.servlet.Filter} and in AOP languages.
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 {@link ActionInvocation} execution and return a return code(such as {@link com.opensymphony.xwork2.Action#SUCCESS}), or it may choose to do some processing before and/or after delegating the rest of the procesing using {@link 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="servletConfig"/> <interceptor-ref name="prepare"/> <interceptor-ref name="i18n"/> <interceptor-ref name="chain"/> <interceptor-ref name="modelDriven"/> <interceptor-ref name="fileUpload"/> <interceptor-ref name="staticParams"/> <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>
Method 2: <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 'interceptor-ref' refer to an existing interceptor-stack, namely defaultStack in this example, and override the validator and workflow interceptor excludeMethods typically in this case. Note that in the 'param' tag, the name attribute contains a dot (.) the word before the dot(.) specifies the interceptor name whose parameter is to be overridden and the word after the dot (.) specifies the parameter itself. Essetially it is as follows :-
<interceptor-name>.<parameter-name>
Note also that in this case the 'interceptor-ref' name attribute is used to indicate an interceptor stack which makes sense as if it is referring to the interceptor itself it would be just using Method 1 describe above.
Nested Interceptor param overriding Interceptor stack parameter overriding could be nested into as many level as possible, though it would be advisable not to nest it too deep as to avoid confusion, For example,
<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>
Assuming the interceptor has the following properties
| Interceptor | property |
| Interceptor1 | param1 |
| Interceptor2 | param2 |
| Interceptor3 | param3 |
| Interceptor4 | param4 |
We could override them as follows :-
<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>
@author Jason Carreira
@author tmjee
@version $Date$ $Id$