Deregister @Configuration CGLIB callbacks

CGLIB-enhanced @Configuration subclasses now implement DisposableBean
such that Enhancer.registerStaticCallbacks(subclass, null) is invoked
on container shutdown. This ensures that garbage collection can work
properly and avoids memory consumption issues for applications that
create and destroy many application contexts within the same JVM.

Issue: SPR-7901

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

@@ -31,6 +31,7 @@ import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.springframework.aop.scope.ScopedProxyFactoryBean;
 import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.FactoryBean;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.core.annotation.AnnotationUtils;
@@ -64,6 +65,7 @@ class ConfigurationClassEnhancer {
 		Assert.notNull(beanFactory, "BeanFactory must not be null");
 
 		this.callbackInstances.add(new BeanMethodInterceptor(beanFactory));
+		this.callbackInstances.add(new DisposableBeanMethodInterceptor());
 		this.callbackInstances.add(NoOp.INSTANCE);
 
 		for (Callback callback : this.callbackInstances) {
@@ -74,7 +76,13 @@ class ConfigurationClassEnhancer {
 		// handling a @Bean-annotated method; otherwise, return index of the NoOp callback.
 		callbackFilter = new CallbackFilter() {
 			public int accept(Method candidateMethod) {
-				return (BeanAnnotationHelper.isBeanAnnotated(candidateMethod) ? 0 : 1);
+				if (BeanAnnotationHelper.isBeanAnnotated(candidateMethod)) {
+					return 0;
+				}
+				if (DisposableBeanMethodInterceptor.isDestroyMethod(candidateMethod)) {
+					return 1;
+				}
+				return 2;
 			}
 		};
 	}
@@ -104,6 +112,7 @@ class ConfigurationClassEnhancer {
 		// any performance problem.
 		enhancer.setUseCache(false);
 		enhancer.setSuperclass(superclass);
+		enhancer.setInterfaces(new Class[] {DisposableBean.class});
 		enhancer.setUseFactory(false);
 		enhancer.setCallbackFilter(this.callbackFilter);
 		enhancer.setCallbackTypes(this.callbackTypes.toArray(new Class[this.callbackTypes.size()]));
@@ -145,6 +154,29 @@ class ConfigurationClassEnhancer {
 	}
 
 
+	/**
+	 * 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.
+	 */
+	private static class DisposableBeanMethodInterceptor implements MethodInterceptor {
+
+		public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
+			Enhancer.registerStaticCallbacks(obj.getClass(), null);
+			if (DisposableBean.class.isAssignableFrom(obj.getClass().getSuperclass())) {
+				return proxy.invokeSuper(obj, args);
+			}
+			return null;
+		}
+
+		public static boolean isDestroyMethod(Method candidateMethod) {
+			return candidateMethod.getName().equals("destroy") &&
+				candidateMethod.getParameterTypes().length == 0 &&
+				DisposableBean.class.isAssignableFrom(candidateMethod.getDeclaringClass());
+		}
+	}
+
+
 	/**
 	 * Intercepts the invocation of any {@link Bean}-annotated methods in order to ensure proper
 	 * handling of bean semantics such as scoping and AOP proxying.

org.springframework.context/src/test/java/org/springframework/context/annotation/configuration/ConfigurationClassCglibCallbackDeregistrationTests.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright 2002-2011 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.context.annotation.configuration;
+
+import static org.hamcrest.CoreMatchers.instanceOf;
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import org.junit.Test;
+import org.springframework.beans.factory.DisposableBean;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Tests ensuring that @Configuration-related CGLIB callbacks are de-registered
+ * at container shutdown time, allowing for proper garbage collection. See SPR-7901.
+ *
+ * @author Chris Beams
+ */
+public class ConfigurationClassCglibCallbackDeregistrationTests {
+
+	/**
+	 * asserting that the actual callback is deregistered is difficult,
+	 * but we can at least assert that the @Configuration class is enhanced
+	 * to implement DisposableBean. The enhanced implementation of destroy()
+	 * will do the de-registration work.
+	 */
+	@Test
+	public void destroyContext() {
+		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(Config.class);
+		Config config = ctx.getBean(Config.class);
+		assertThat(config, instanceOf(DisposableBean.class));
+		ctx.destroy();
+	}
+
+	/**
+	 * The DisposableBeanMethodInterceptor in ConfigurationClassEnhancer
+	 * should be careful to invoke any explicit super-implementation of
+	 * DisposableBean#destroy().
+	 */
+	@Test
+	public void destroyExplicitDisposableBeanConfig() {
+		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(DisposableConfig.class);
+		DisposableConfig config = ctx.getBean(DisposableConfig.class);
+		assertThat(config.destroyed, is(false));
+		ctx.destroy();
+		assertThat("DisposableConfig.destroy() was not invoked", config.destroyed, is(true));
+	}
+
+
+	@Configuration
+	static class Config {
+	}
+
+
+	@Configuration
+	static class DisposableConfig implements DisposableBean {
+		boolean destroyed = false;
+		public void destroy() throws Exception {
+			this.destroyed = true;
+		}
+	}
+}