Remove DisposableBeanMethodInterceptor

Previously, any @configuration class was enhanced to namely implement
DisposableBean in order to remove static callbacks that were registered
for that class. This leads to problem if an ApplicationContext is created
and destroyed within the lifecycle on another ApplicationContext in the
same class loader.

It turns out that the destruction callback is no longer necessary as the
interceptors are now stateless: the VM is free to reclaim any of those if
necessary.

Issue: SPR-12445

Author: snicoll

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassEnhancer.java

@@ -27,7 +27,6 @@
 import org.springframework.asm.Type;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
-import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.beans.factory.support.SimpleInstantiationStrategy;
@@ -65,9 +64,9 @@
  */
 class ConfigurationClassEnhancer {
 
+	// The callbacks to use. Note that these callbacks must be stateless.
 	private static final Callback[] CALLBACKS = new Callback[] {
 			new BeanMethodInterceptor(),
-			new DisposableBeanMethodInterceptor(),
 			new BeanFactoryAwareMethodInterceptor(),
 			NoOp.INSTANCE
 	};
@@ -139,15 +138,13 @@ private Class<?> createClass(Enhancer enhancer) {
 	 * Facilitates idempotent behavior for {@link ConfigurationClassEnhancer#enhance(Class)}
 	 * through checking to see if candidate classes are already assignable to it, e.g.
 	 * have already been enhanced.
-	 * <p>Also extends {@link DisposableBean} and {@link BeanFactoryAware}, as all
-	 * enhanced {@code @Configuration} classes require access to the {@link BeanFactory}
-	 * that created them and must de-register static CGLIB callbacks on destruction,
-	 * which is handled by the (private) {@code DisposableBeanMethodInterceptor}.
+	 * <p>Also extends {@link BeanFactoryAware}, as all enhanced {@code @Configuration}
+	 * classes require access to the {@link BeanFactory} that created them.
 	 * <p>Note that this interface is intended for framework-internal use only, however
 	 * must remain public in order to allow access to subclasses generated from other
 	 * packages (i.e. user code).
 	 */
-	public interface EnhancedConfiguration extends DisposableBean, BeanFactoryAware {
+	public interface EnhancedConfiguration extends BeanFactoryAware {
 	}
 
 
@@ -403,32 +400,4 @@ public boolean isMatch(Method candidateMethod) {
 		}
 	}
 
-
-	/**
-	 * Intercepts the invocation of any {@link DisposableBean#destroy()} on @Configuration
-	 * class instances for the purpose of de-registering CGLIB callbacks. This helps avoid
-	 * garbage collection issues. See SPR-7901.
-	 * @see EnhancedConfiguration
-	 */
-	private static class DisposableBeanMethodInterceptor implements MethodInterceptor, ConditionalCallback {
-
-		@Override
-		public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
-			Enhancer.registerStaticCallbacks(obj.getClass(), null);
-			// Does the actual (non-CGLIB) superclass actually implement DisposableBean?
-			// If so, call its dispose() method. If not, just exit.
-			if (DisposableBean.class.isAssignableFrom(obj.getClass().getSuperclass())) {
-				return proxy.invokeSuper(obj, args);
-			}
-			return null;
-		}
-
-		@Override
-		public boolean isMatch(Method candidateMethod) {
-			return candidateMethod.getName().equals("destroy") &&
-					candidateMethod.getParameterTypes().length == 0 &&
-					DisposableBean.class.isAssignableFrom(candidateMethod.getDeclaringClass());
-		}
-	}
-
 }