Allow @Aspect classes to extend concrete @Aspect classes

Closes gh-29830

spring-aop/src/main/java/org/springframework/aop/aspectj/annotation/AbstractAspectJAdvisorFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,7 +20,6 @@ import java.lang.annotation.Annotation;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
-import java.lang.reflect.Modifier;
 import java.util.Map;
 import java.util.StringTokenizer;
 
@@ -52,6 +51,7 @@ import org.springframework.lang.Nullable;
  * @author Rod Johnson
  * @author Adrian Colyer
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 2.0
  */
 public abstract class AbstractAspectJAdvisorFactory implements AspectJAdvisorFactory {
@@ -101,14 +101,6 @@ public abstract class AbstractAspectJAdvisorFactory implements AspectJAdvisorFac
 
 	@Override
 	public void validate(Class<?> aspectClass) throws AopConfigException {
-		// If the parent has the annotation and isn't abstract it's an error
-		Class<?> superclass = aspectClass.getSuperclass();
-		if (superclass.getAnnotation(Aspect.class) != null &&
-				!Modifier.isAbstract(superclass.getModifiers())) {
-			throw new AopConfigException("[" + aspectClass.getName() + "] cannot extend concrete aspect [" +
-					superclass.getName() + "]");
-		}
-
 		AjType<?> ajType = AjTypeSystem.getAjType(aspectClass);
 		if (!ajType.isAspect()) {
 			throw new NotAnAtAspectException(aspectClass);