EJB runtime context, dependency injection, and crosscutting logic - EJB 3 in Action - page 201

In effect, this means that the logMethodEntry() method will be executed whenever
the ActionBazaarLogger interceptor is triggered. As you might gather from this code,
any method designated @AroundInvoke must follow this pattern:
Object <METHOD>(InvocationContext) throws Exception
The InvocationContext interface passed in as the single parameter to the method
provides a number of features that make the AOP mechanism extremely flexible. The
logMethodEntry() method uses just two of the methods included in the interface.
The getMethod().getName() call returns the name of the method being intercep-
ted— "addBid" in this case.
The call to the proceed() method is extremely critical to the functioning of the intercept-
or. This tells the container it should proceed to the next interceptor in the execution chain
or call the intercepted business method. On the other hand, not calling the proceed()
method will bring processing to a halt and prevent the business method (and any other in-
terceptor down the execution chain) from being called.
This feature can be extremely useful for procedures like security validation. For example,
the following interceptor method prevents the intercepted business method from being ex-
ecuted if security validation fails:
@AroundInvoke
public Object validateSecurity(InvocationContext invocationContext)
throws Exception {
if (!validate(...)) {
throw new SecurityException("Security cannot be validated. " +
"The method invocation is being blocked.");
}
return invocationContext.proceed();
}
The InvocationContext interface
The following listing shows that the javax.interceptor.InvocationContext
interface has a number of other useful methods.
Listing 5.11. javax.interceptor.InvocationContext interface
public interface InvocationContext {
public Object getTarget();
public Method getMethod();