What are interceptors in Struts2 ?

Interceptors

• allow custom code into the call stack
• Much of the core functionality of the framework is implemented as Interceptors
• Custom Interceptors are easy to add

Example 1. Logging interceptor

public class LoggingInterceptor implements Interceptor {

   public String intercept(ActionInvocation invocation) 

                 throws Exception {

        logMessage(invocation, START_MESSAGE);

        String result = invocation.invoke();

        logMessage(invocation, FINISH_MESSAGE);

return result;

}

}

Example 2. Timer interceptor

public class TimerInterceptor implements Interceptor {

   public String intercept(ActionInvocation invocation) 

                 throws Exception {

      if (log.isInfoEnabled()) {

         long startTime = System.currentTimeMillis();

         String result = invocation.invoke();

         long executionTime =System.currentTimeMillis() - startTime;

         ...

      } 

   }

}

Other Interceptors

Setting Parameters

• ParameterInterceptor
• StaticParameterInterceptor
• ChainingInterceptor
• ConversionErrorInterceptor
• FileUploadInterceptor

Defining Workflow

• DefaultWorkflowInterceptor
• PrepareInterceptor
• ServletConfigInterceptor
• ExecuteAndWaitInterceptor

Preventing duplicate posts

• Two types of token interceptors