Getting a return value or exception from AspectJ?

Question

I am able to get the signature and arguments from advised method calls, but I cannot figure out how to get the return values or exceptions. I'm kind of assuming that it can be done in some way using around and proceed.

Answer 1

You can use after() returning and after() throwing advices as in beginning of the following document. If you're using @AspectJ syntax please refer to @AfterReturning and @AfterThrowing annotations (you can find samples here).

Answer 2

You can also get return value using after returing advice.

package com.eos.poc.test;   

public class AOPDemo {
            public static void main(String[] args) {
                AOPDemo demo = new AOPDemo();
                String result= demo.append("Eclipse", " aspectJ");
           }
            public String append(String s1, String s2) {
                System.out.println("Executing append method..");
                return s1 + s2;
          }

}

The defined aspect for getting return value:

public aspect DemoAspect {
    pointcut callDemoAspectPointCut():
        call(* com.eos.poc.test.AOPDemo.append(*,*));

    after() returning(Object r) :callDemoAspectPointCut(){
        System.out.println("Return value: "+r.toString()); // getting return value

    }

Answer 3

Using an around() advice, you can get the return value of the intercepted method call by using proceed(). You can even change the value returned by the method if you want to.

For instance, suppose you have a method m() inside class MyClass:

public class MyClass {
  int m() {
    return 2;
  }
}

Suppose you have the following aspect in its own .aj file:

public aspect mAspect {
   pointcut mexec() : execution(* m(..));

   int around() : mexec() {    
     // use proceed() to do the computation of the original method
     int original_return_value = proceed();

     // change the return value of m()
     return original_return_value * 100;
   }
}