AspectJ - meta/nested annotation parameter binding

Question

I have defined a meta annotation and a number of concrete annotations annotated with the meta. I am currently trying to implement an aspect that would weave methods annotated with these concrete annotations based on the meta annotation. I was able to use this pointcut to achieve the advice invocation.

"execution(@(@my.meta.Annotation *) * *(..))"

However, I would like to make use of parameter binding because the meta annotation defines a field whose value I am interested in. Unfortunatelly, I was not able to find a correct expression to achieve that.

Is it possible to use parameter binding when using a nested annotation pointcut or do I need to get the annotation from JoinPoint?

Answer 1

Annotation binding via @annotation(), @within() needs an exact class, but you want a generic solution. Therefore, you do need to fetch the annotation from the method via reflection, i.e. you need to take the route:

joinpoint → signature → method → annotation → meta annotation

package de.scrum_master.stackoverflow.q75834894.app;

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

@Retention(RUNTIME)
public @interface Meta {
  String id();
}

package de.scrum_master.stackoverflow.q75834894.app;

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

@Retention(RUNTIME)
@Meta(id = "indirect")
public @interface Marker {}

package de.scrum_master.stackoverflow.q75834894.app;

public class Application {
  public static void main(String[] args) {
    Application application = new Application();
    application.notAnnotated();
    application.metaAnnotated();
    application.markerAnnotated();
  }

  public void notAnnotated() {}
  @Meta(id = "direct") public void metaAnnotated() {}
  @Marker public void markerAnnotated() {}
}

package de.scrum_master.stackoverflow.q75834894.aspect;

import java.lang.annotation.Annotation;
import org.aspectj.lang.reflect.MethodSignature;
import de.scrum_master.stackoverflow.q75834894.app.Meta;

public aspect MyAspect {
  before(Meta meta) : @annotation(meta) && execution(* *(..)) {
    System.out.println(thisJoinPoint);
    System.out.println("  " + meta.id());
  }

  before() : execution(@(@de.scrum_master.stackoverflow.q75834894.app.Meta *) * *(..)) {
    System.out.println(thisJoinPoint);
    for (Annotation annotation : ((MethodSignature) thisJoinPoint.getSignature()).getMethod().getAnnotations()) {
      Meta meta = annotation.annotationType().getAnnotation(Meta.class);
      if (meta != null)
        System.out.println("  " + meta.id());
    }
  }
}

I guess you know how how to convert the native syntax aspect into annotation-based aspect syntax, if you prefer that.

The console log:

execution(void de.scrum_master.stackoverflow.q75834894.app.Application.metaAnnotated())
  direct
execution(void de.scrum_master.stackoverflow.q75834894.app.Application.markerAnnotated())
  indirect