Difference between @target and @within (Spring AOP)

Question

Spring manual says:

any join point (method execution only in Spring AOP) where the target object has an @Transactional annotation: @target(org.spring

Answer 1

The informations you have quoted are correct, however only @target pointcut designators require annotations with RUNTIME retention, while @within only requires CLASS retention.

Let's consider the following two simple annotations:

ClassRetAnnotation.java

package mypackage;

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

@Retention(RetentionPolicy.CLASS)
public @interface ClassRetAnnotation {}

RuntimeRetAnnotation.java

package mypackage;

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

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

Now, if you define an aspect like the following one, there will be no exception at runtime:

@Component
@Aspect
public class MyAspect {

    @Before("@within(mypackage.ClassRetAnnotation)")
    public void within() { System.out.println("within"); }

    @Before("@target(mypackage.RuntimeRetAnnotation)")
    public void target() { System.out.println("target"); }
}

I hope this example helped to clarify the subtle difference you pointed.

Spring reference: https://docs.spring.io/spring/docs/5.0.x/spring-framework-reference/core.html#aop-pointcuts