AspectJ pointcut expression match parameter annotations at any position

Question

I'm trying to define a pointcut expression to match methods which contain a parameter annotated with a specific annotation, regardless of what position the parameter is in. In my case I'm looking for the @Constraint annotation. For example:

Matching methods:

public void method1(@Constraint Car car)

public void method2(String id, @Constraint Plane plane)

public void method3(Wheel wheel, @Constraint List<Train> trains, @Constraint Plane plane)

public void method4(Motor motor, @Constraint Set<Train> trains, Bicycle bike, Wheel wheel)

public void method5(Wing wing, Motorcycle moto, @Constraint Truck truck, Bicycle bike, Wheel wheel)

So far I've tried the following expressions with no luck:

@Before("execution(public * *.*(..)) and @args(com.example.Constraint)") // there can be only one parameter
@Before("execution(public * *.*(..)) and @args(..,com.example.Constraint)") // parameter must be in last position
@Before("execution(public * *.*(..)) and @args(com.example.Constraint,..)") // parameter must be in first position
@Before("execution(public * *.*(..)) and (@args(com.example.Constraint,..) or @args(..,com.example.Constraint))") // parameter must be in first or last position, nothing in between
@Before("execution(public * *.*(..)) and @args(..,com.example.Constraint,..)") // Invalid

Can someone point me to the right solution? is it even possible?

Answer 1

You cannot bind an argument at an arbitrary position via args() in AspectJ because this could lead to ambiguity. Just imagine you have two or more parameters of the same type (or annotated by the same annotation type in this case). Which one of them should be bound to the named args() parameter? So while

execution(public * *(.., @Deprecated (*), ..))

is possible as a stand-alone expression (please note the parentheses around the star), it is not possible in combination with args(). So if you do not just want to intercept the method execution itself, but also find the first or all parameters with the given annotation you need to do just what I showed in the other article. I am kinda repeating myself, but so be it in order for the answer not to be deleted again:

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Retention(RetentionPolicy.RUNTIME)
public @interface Constraint {}

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class Application {
    public void method1(@Constraint int i) {}
    public void method2(String id, @Constraint float f) {}
    public void method3(int i, @Constraint List<String> strings, @Constraint String s) {}
    public void method4(int i, @Constraint Set<Integer> numbers, float f, boolean b) {}
    public void method5(boolean b, String s, @Constraint String s2, float f, int i) {}
    public void notIntercepted(boolean b, String s, String s2, float f, int i) {}

    public static void main(String[] args) {
        List<String> strings = new ArrayList<String>();
        strings.add("foo");
        strings.add("bar");
        Set<Integer> numbers = new HashSet<Integer>();
        numbers.add(11);
        numbers.add(22);
        numbers.add(33);

        Application app = new Application();
        app.method1(1);
        app.method2("foo", 1f);
        app.method3(1, strings, "foo");
        app.method4(1, numbers, 1f, true);
        app.method5(false, "foo", "bar", 1f, 1);
        app.notIntercepted(false, "foo", "bar", 1f, 1);
    }
}

import java.lang.annotation.Annotation;

import org.aspectj.lang.SoftException;
import org.aspectj.lang.reflect.MethodSignature;

public aspect ArgCatcherAspect {
    before() : execution(public * *(.., @Constraint (*), ..)) {
        System.out.println(thisJoinPointStaticPart);
        MethodSignature signature = (MethodSignature) thisJoinPoint.getSignature();
        String methodName = signature.getMethod().getName();
        Class<?>[] parameterTypes = signature.getMethod().getParameterTypes();
        Annotation[][] annotations;
        try {
            annotations = thisJoinPoint.getTarget().getClass().
                getMethod(methodName, parameterTypes).getParameterAnnotations();
        } catch (Exception e) {
            throw new SoftException(e);
        }
        int i = 0;
        for (Object arg : thisJoinPoint.getArgs()) {
            for (Annotation annotation : annotations[i]) {
                if (annotation.annotationType() == Constraint.class)
                    System.out.println("  " + annotation + " -> " + arg);
            }
            i++;
        }
    }
}

As you can see, it is a bit trickier to get the annotations of a given parameter than just its declared type, but basically it works the same way as in my previous post, i.e. by iterating over the list of arguments.