Pointcuts are specified using the org.aspectj.lang.annotation.Pointcut annotation on a method declaration. The method should have a void return type. The parameters of the method correspond to the parameters of the pointcut. The modifiers of the method correspond to the modifiers of the pointcut.

As a general rule, the @Pointcut annotated method must have an empty method body and must not have any throws clause. If formal are bound (using args(), target(), this(), @args(), @target(), @this(), @annotation()) in the pointcut, then they must appear in the method signature.

The if() pointcut is treated specially and is discussed in a later section.

Here is a simple example of a pointcut declaration in both code and @AspectJ styles:

     @Pointcut("call(* *.*(..))")
     void anyCall() {}
         

is equivalent to...

     pointcut anyCall() : call(* *.*(..));
             

When binding arguments, simply declare the arguments as normal in the annotated method:

     @Pointcut("call(* *.*(int)) && args(i) && target(callee)")
     void someCall(int i, Foo callee) {}
         

is equivalent to...

     pointcut anyCall(int i, Foo callee) : call(* *.*(int)) && args(i) && target(callee);
             

An example with modifiers (Remember that Java 5 annotations are not inherited, so the @Pointcut annotation must be present on the extending aspect's pointcut declaration too):

     @Pointcut("")
     protected abstract void anyCall();
         

is equivalent to...

     protected abstract pointcut anyCall();
             

     package org.aspectprogrammer.examples;

     import java.util.List;

     public aspect Foo {

       pointcut listOperation() : call(* List.*(..));

       pointcut anyUtilityCall() : call(* java.util..*(..));

     }
             

     package org.aspectprogrammer.examples;

     import java.util.List; // redundant but harmless

     @Aspect
     public class Foo {

       @Pointcut("call(* java.util.List.*(..))") // must qualify
       void listOperation() {}

       @Pointcut("call(* java.util..*(..))")
       void anyUtilityCall() {}

     }
             

     @Pointcut("call(* *.*(int)) && args(i) && if()")
     public static boolean someCallWithIfTest(int i) {
        return i > 0;
     }
         

     pointcut someCallWithIfTest(int i) : call(* *.*(int)) && args(i) && if(i > 0);
             

     static int COUNT = 0;

     @Pointcut("call(* *.*(int)) && args(i) && if()")
     public static boolean someCallWithIfTest(int i, JoinPoint jp, JoinPoint.EnclosingStaticPart esjp) {
        // any legal Java expression...
        return i > 0
               && jp.getSignature().getName.startsWith("doo")
               && esjp.getSignature().getName().startsWith("test")
               && COUNT++ < 10;
     }

     @Before("someCallWithIfTest(anInt, jp, enc)") 
     public void beforeAdviceWithRuntimeTest(int anInt, JoinPoint jp, JoinPoint.EnclosingStaticPart enc) {
        //...
     }

     // Note that the following is NOT valid
     /*
     @Before("call(* *.*(int)) && args(i) && if()")
     public void advice(int i) {
        // so you were writing an advice or an if body ?
     }
     */
             

In this section we first discuss the use of annotations for simple advice declarations. Then we show how thisJoinPoint and its siblings are handled in the body of advice and discuss the treatment of proceed in around advice.

Using the annotation style, an advice declaration is written as a regular Java method with one of the Before, After, AfterReturning, AfterThrowing, or Around annotations. Except in the case of around advice, the method should return void. The method should be declared public.

A method that has an advice annotation is treated exactly as an advice declaration by AspectJ's weaver. This includes the join points that arise when the advice is executed (an adviceexecution join point, not a method execution join point).

The following example shows a simple before advice declaration in both styles:

     @Before("call(* org.aspectprogrammer..*(..)) && this(Foo)")
     public void callFromFoo() {
       System.out.println("Call from Foo");
     }
             

is equivalent to...

     before() : call(* org.aspectprogrammer..*(..)) && this(Foo) {
       System.out.println("Call from Foo");
     }
         

If the advice body needs to know which particular Foo instance is making the call, just add a parameter to the advice declaration.

     before(Foo foo) : call(* org.aspectprogrammer..*(..)) && this(foo) {
       System.out.println("Call from Foo: " + foo);
     }
             

can be written as:

     @Before("call(* org.aspectprogrammer..*(..)) && this(foo)")
     public void callFromFoo(Foo foo) {
       System.out.println("Call from Foo: " + foo);
     }
             

If the advice body needs access to thisJoinPoint , thisJoinPointStaticPart , thisEnclosingJoinPointStaticPart then these need to be declared as additional method parameters when using the annotation style.

     @Before("call(* org.aspectprogrammer..*(..)) && this(foo)")
     public void callFromFoo(JoinPoint thisJoinPoint, Foo foo) {
       System.out.println("Call from Foo: " + foo + " at "
                          + thisJoinPoint);
     }
             

is equivalent to...

     before(Foo foo) : call(* org.aspectprogrammer..*(..)) && this(foo) {
       System.out.println("Call from Foo: " + foo + " at "
                          + thisJoinPoint);
     }
            

Advice that needs all three variables would be declared:

     @Before("call(* org.aspectprogrammer..*(..)) && this(Foo)")
     public void callFromFoo(JoinPoint thisJoinPoint,
                             JoinPoint.StaticPart thisJoinPointStaticPart,
                             JoinPoint.EnclosingStaticPart thisEnclosingJoinPointStaticPart) {
         // ...
     }
             

JoinPoint.EnclosingStaticPart is a new (empty) sub-interface of JoinPoint.StaticPart which allows the AspectJ weaver to distinguish based on type which of thisJoinPointStaticPart and thisEnclosingJoinPointStaticPart should be passed in a given parameter position.

After advice declarations take exactly the same form as Before , as do the forms of AfterReturning and AfterThrowing that do not expose the return type or thrown exception respectively.

To expose a return value with after returning advice simply declare the returning parameter as a parameter in the method body and bind it with the "returning" attribute:

      @AfterReturning("criticalOperation()")
      public void phew() {
        System.out.println("phew");
      }

      @AfterReturning(pointcut="call(Foo+.new(..))",returning="f")
      public void itsAFoo(Foo f) {
        System.out.println("It's a Foo: " + f);
      }
            

is equivalent to...

      after() returning : criticalOperation() {
        System.out.println("phew");
      }

      after() returning(Foo f) : call(Foo+.new(..)) {
        System.out.println("It's a Foo: " + f);
      }
            

(Note the use of the "pointcut=" prefix in front of the pointcut expression in the returning case).

After throwing advice works in a similar fashion, using the throwing attribute when needing to expose a thrown exception.

For around advice, we have to tackle the problem of proceed . One of the design goals for the annotation style is that a large class of AspectJ applications should be compilable with a standard Java 5 compiler. A straight call to proceed inside a method body:

     @Around("call(* org.aspectprogrammer..*(..))")
     public Object doNothing() {
       return proceed(); // CE on this line
     }
             

will result in a "No such method" compilation error. For this reason AspectJ 5 defines a new sub-interface of JoinPoint , ProceedingJoinPoint .

     public interface ProceedingJoinPoint extends JoinPoint {
       public Object proceed(Object[] args);
     }
             

The around advice given above can now be written as:

     @Around("call(* org.aspectprogrammer..*(..))")
     public Object doNothing(ProceedingJoinPoint thisJoinPoint) {
       return thisJoinPoint.proceed();
     }
             

Here's an example that uses parameters for the proceed call:

     @Aspect
     public class ProceedAspect {

       @Pointcut("call(* setAge(..)) && args(i)")
       void setAge(int i) {}

       @Around("setAge(i)")
       public Object twiceAsOld(ProceedingJoinPoint thisJoinPoint, int i) {
         return thisJoinPoint.proceed(new Object[]{i*2}); //using Java 5 autoboxing
       }

     }

             

is equivalent to:

     public aspect ProceedAspect {
       pointcut setAge(int i): call(* setAge(..)) && args(i);

       Object around(int i): setAge(i) {
         return proceed(i*2);
       }
     }
            

Note that the ProceedingJoinPoint does not need to be passed to the proceed(..) arguments.

In code style, the proceed method has the same signature as the advice, any reordering of actual arguments to the joinpoint that is done in the advice signature must be respected. Annotation style is different. The proceed(..) call takes, in this order:

Since proceed(..) in this case takes an Object array, AspectJ cannot do as much compile time checking as it can for code style. If the rules above aren't obeyed then it will unfortunately manifest as a runtime error.