How to write an Aspect pointcut based on an annotated parameter

Question

I'm having a bit of trouble working out how to create a pointcut that will operate on beans that have a specific annotated parameter. My eventual aim is to validate the value of the parameter before it's processed, but for the moment I just need to create the pointcut.

Consider the following annotation

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.PARAMETER })
public @interface MyAnnotation {}

I'd then like to apply this to a number of methods like:

public void method1(@MyAnnotation long i) {}
public void method2(String someThing, @MyAnnotation long i) {}
public void method3(String someThing, @MyAnnotation long i, byte value) {}

So

• I don't care which class (or package) the methods are in
• The position of the annotated argument will vary.
• I do know that annotated value will only apply to a specific type

My pointcut implementation needs to be something along the lines of:

@Before(value = "* *(..) && args(verifyMe)")
public void verifyInvestigationId(long verifyMe) {}

I'm getting a bit confused about exactly what that @Before value needs to be and how to tie in the annotation and its type. At this point it's probably not worth listing the things I've tried!

Update: Based on the advice I've seen in http://stackoverflow.com/questions/3565718/pointcut-matching-methods-with-annotated-parameters/3567170#3567170 (and correcting a couple of misunderstandings and adding space I overlooked) I've got to the point where the following works:

@Before("execution(public * *(.., @full.path.to.MyAnnotation (*), ..))")
public void beforeMethod(JoinPoint joinPoint) {
    System.out.println("At least one of the parameters are annotated with @MyAnnotation");
}

This is almost what I need - all I need to do is pass the value of the annotated argument as an parameter to the method. I can't quite work out the syntax to get Spring to do this (the linked answer does not show this).

Answer 1

Very similar to my answer here which sheltem already pointed to, the solution looks like this (in annotation-style syntax this time because in Spring AOP you cannot use native AspectJ syntax):

Original poster's annotation:

package annotations;

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

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.PARAMETER })
public @interface MyAnnotation {}

Driver Application:

I use the driver application in order to test my AspectJ solution. In Spring the class as well as the aspect need to be Spring beans/components in order for this to work.

package de.scrum_master.app;

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

import annotations.MyAnnotation;

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

Aspect:

package de.scrum_master.aspect;

import java.lang.annotation.Annotation;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.SoftException;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.reflect.MethodSignature;

import annotations.MyAnnotation;

@Aspect
public class ArgCatcherAspect {
    @Before("execution(public * *(.., @MyAnnotation (*), ..))")
    public void interceptMethodsWithAnnotatedParameters(JoinPoint thisJoinPoint) {
        System.out.println(thisJoinPoint);
        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() == MyAnnotation.class) {
                    System.out.println("  " + annotation + " -> " + arg);
                    // Verify 'arg' here or do whatever
                }
            }
            i++;
        }
    }
}

Console log:

execution(void de.scrum_master.app.Application.method1(int))
  @annotations.MyAnnotation() -> 1
execution(void de.scrum_master.app.Application.method2(String, float))
  @annotations.MyAnnotation() -> 1.0
execution(void de.scrum_master.app.Application.method3(int, List, String))
  @annotations.MyAnnotation() -> [foo, bar]
  @annotations.MyAnnotation() -> foo
execution(void de.scrum_master.app.Application.method4(int, Set, float, boolean))
  @annotations.MyAnnotation() -> [33, 22, 11]
execution(void de.scrum_master.app.Application.method5(boolean, String, String, float, int))
  @annotations.MyAnnotation() -> bar

Answer 2

This is what I ended up at after fiddling about with it (imports omitted):

@Aspect
public class VerifyAspect {

    @Before("execution(* *(.., @annotations.MyAnnotation (*), ..)) && args(.., verifyMe)")
    public void verifyInvestigationId(final Object verifyMe) {
        System.out.println("Aspect verifying: " + verifyMe);
    }
}

No need for anything Spring-specific, as AspectJ already provides you with the parameters if so desired.