See the Interceptors page for an overview of how interceptors work.
Interceptors must implement the com.opensymphony.xwork2.interceptor.Interceptor interface.
The init method is called the interceptor is instantiated and before calling intercept. This is the place to allocate any resources used by the interceptor.
The intercept method is where the interceptor code is written. Just like an action method, intercept returns a result used by Struts to forward the request to another resource. Calling invoke on the parameter of type ActionInvocation will execute the action (if this is the last interceptor on the stack) or another interceptor.
Overwrite destroy to release resources.
The AbstractInterceptor class provides an empty implementation of init and destroy, and can be used if these methods are not going to be implemented.
Assuming there is an action of type "MyAction", with a setDate(Date) method, this simple interceptor will set the date of the action to the current date: