MindSpace

Enum value matching using AspectJ

I wrote an Aspect to advise a particular constant-specific method.

What is a constant-specific method ?

The J2SE 5 documentation explains it.

“You can declare the method abstract in the enum type and override it with a concrete method in each constant. Such methods are known as constant-specific methods.”

There is an example here.

The enum is

package com.test.generics;

import java.util.Collection;
import java.util.List;
import java.util.Set;

public enum TestEnum {
    Value1{
        public &lt;T> List<T> getValue(){ return null; }
        public <T> List<T> getSameValue(){ return null; }
   },
   Value2{
        public <T> Set <T>getValue(){ return null; }
        public <T> List<T> getSameValue(){ return null; }
   };

   abstract <T> Collection<T> getValue();

   abstract <T> Collection<T> getSameValue();

	public static void main(String[] args) {
		System.out.println( Value1.getSameValue() );
		System.out.println( Value2.getSameValue() );
	}

}

package com.test;

import java.util.List;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import com.test.generics.TestEnum;

@Aspect()
public class EnumAspect {

              /*
                  Matches a particular method of all enum values
               */             
	@Pointcut(
	"execution(List<T> getValue())" )
	public void testPointcut(){};

	@Before("testPointcut()")
	public void test() {
		System.out.println( "Generics aspect" );
	}

                /*
                  Matches a method of a particular enum values
               */   

	@Pointcut(
	"execution(List<T> getSameValue()) && target(testEnum) && if()")
	public static boolean testPointcut1( TestEnum testEnum ){
		return testEnum == TestEnum.Value2;
	}

	@Before("testPointcut1(testEnum)")
	public void test1( TestEnum testEnum ) {
		System.out.println( "Generics aspect [" + testEnum.ordinal() + "]" );
	}

}

The if() pointcut expression with an empty body is used and the testPointcut1 method tests for the value of the enum. There does not seem to be a JoinPoint matching pattern to pick out certain enum values automatically. It looks like a pattern would be useful.

Update : Raised an enhancement request.

Update : 26 Oct 2020

One of the contributors who has commented here pointed out that this aspect works. I am not sure if this would have worked 12 years back when I raised the request. At that time I thought it was a missing feature.

@Aspect
public class EnumAspect {
@Pointcut("execution(java.util.Collection+ getValue()) && target(testEnum) && if()")
public static boolean testPointcut1(TestEnum testEnum) {
return testEnum == TestEnum.Value1;
}

@Before("testPointcut1(testEnum)")
public void test1(JoinPoint joinPoint, TestEnum testEnum) {
System.out.println(joinPoint + " -> " + testEnum);
}

@Pointcut("execution(java.util.Collection+ getValue()) && target(testEnum) && if()")
public static boolean testPointcut2(TestEnum testEnum) {
return testEnum == TestEnum.Value2;
}

@Before("testPointcut2(testEnum)")
public void test2(JoinPoint joinPoint, TestEnum testEnum) {
System.out.println(joinPoint + " -> " + testEnum);
}

}