Why should the return type of a timeout method interceptor be Object?

[You Peng]

Hi there,

can someone help me with this? Returning an Object from a business method interceptor would make some sense, but since a timeout method always returns void, why?

Thanks,
Y.P.

[Himai Minh]

Timer does not have any client. So, timeout method does not return any value to the client.
Timer is invoked by the container, but not by the client. It is not necessary for a timer to return any value.
Hope this helps.

[You Peng]

Hi Himai,

Thanks for the reply. But since it's the container, not the client, who calls the time out callback, I thought the callback should *never* return an object, which then makes "an interceptor for a timeout method returning an object" unreasonable/useless. Am I wrong with "timeout callbacks should never return an object"? Or is the return value of the interceptor meant for something else?

You

[Himai Minh]

Timeout method does not return anything. The container calls the timeout method when the scheduler time is up.
The client does not invoke the timeout method. So, it is not necessary for timeout method to return any value.

Interceptors (except those lifecycle callback interceptors, @PostConstruct, @PreDestroy....) can return an Object type.
Typically, an interceptor method is like this:

public Object myInterceptor (InvocationContext ic) throws Exception{
   
 //... do something here before intercepting a business method
  //.... code....
    
    //move on to the business method or another interceptor in the chain
    Object obj= ic.proceed();

    //do something after intercepting a business method or after another interceptor in the chain
    //...code .....

   //then returns the value from ic.proceed() back to the client.
   return obj;


}

[You Peng]

I have no problem with these. But my question is: since timeout callbacks don't produce any result by themselves, and their interceptors are called by the container, which probably don't expect any return value from the interceptors anyway, what's the point of declaring such interceptors to return Object? The situation seems pretty much like that with life cycle interceptors, but the life cycle interceptors can only return void. Why?

[Himai Minh]

I see what you are talking about now.
@AroundTimeout method returns object. But those @PostConstruct ... lifecycle callback interceptors return void.
Maybe, there is some business logic inside the @AroundTimeout method and we may need the business logic to return some values.

I am not sure the exact reason neither.

[You Peng]

Thanks anyway!

[Himai Minh]

Hi, You Peng,
I found this API spec :http://docs.oracle.com/javaee/6/api/javax/interceptor/AroundTimeout.html
It says the @AroundTimeout method may return the timer.

InvocationContext.getTimer() allows any AroundTimeout method to retrieve the timer object associated with the timeout.

[You Peng]

Hi Himai, but that's not what the quote was saying. The quote says only the timer object is accessible from within the method annotated with @AroundTimer.

[Himai Minh]

I think the @AroundTimeout
can return the Timer object.
I am not sure about that.