MBeanExporter implements newly introduced SmartInitializingSingleton callback interface

Issue: SPR-8045

spring-beans/src/main/java/org/springframework/beans/factory/SmartInitializingSingleton.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2002-2014 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.beans.factory;
+
+/**
+ * Callback interface triggered at the end of the singleton pre-instantiation phase
+ * during {@link BeanFactory} bootstrap. This interface can be implemented by
+ * singleton beans in order to perform some initialization after the regular
+ * singleton instantiation algorithm, avoiding side effects with accidental early
+ * initialization (e.g. from {@link ListableBeanFactory#getBeansOfType} calls).
+ * In that sense, it is an alternative to {@link InitializingBean} which gets
+ * triggered right at the end of a bean's local construction phase.
+ *
+ * <p>This callback variant is somewhat similar to
+ * {@link org.springframework.context.event.ContextRefreshedEvent} but doesn't
+ * require an implementation of {@link org.springframework.context.ApplicationListener},
+ * with no need to filter context references across a context hierarchy etc.
+ * It also implies a more minimal dependency on just the {@code beans} package
+ * and is being honored by standalone {@link ListableBeanFactory} implementations,
+ * not just in an {@link org.springframework.context.ApplicationContext} environment.
+ *
+ * <p><b>NOTE:</b> If you intend to start/manage asynchronous tasks, preferably
+ * implement {@link org.springframework.context.Lifecycle} instead which offers
+ * a richer model for runtime management and allows for phased startup/shutdown.
+ *
+ * @author Juergen Hoeller
+ * @since 4.1
+ * @see org.springframework.beans.factory.config.ConfigurableListableBeanFactory#preInstantiateSingletons()
+ */
+public interface SmartInitializingSingleton {
+
+	/**
+	 * Invoked right at the end of the singleton pre-instantiation phase,
+	 * with a guarantee that all regular singleton beans have been created
+	 * already. {@link ListableBeanFactory#getBeansOfType} calls within
+	 * this method won't trigger accidental side effects during bootstrap.
+	 * <p><b>NOTE:</b> This callback won't be triggered for singleton beans
+	 * lazily initialized on demand after {@link BeanFactory} bootstrap,
+	 * and not for any other bean scope either. Carefully use it for beans
+	 * with the intended bootstrap semantics only.
+	 */
+	void afterSingletonsInstantiated();
+
+}

spring-beans/src/main/java/org/springframework/beans/factory/support/DefaultListableBeanFactory.java

@@ -56,6 +56,7 @@ import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.NoUniqueBeanDefinitionException;
 import org.springframework.beans.factory.ObjectFactory;
 import org.springframework.beans.factory.SmartFactoryBean;
+import org.springframework.beans.factory.SmartInitializingSingleton;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanDefinitionHolder;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
@@ -684,12 +685,15 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 		if (this.logger.isDebugEnabled()) {
 			this.logger.debug("Pre-instantiating singletons in " + this);
 		}
+
 		List<String> beanNames;
 		synchronized (this.beanDefinitionMap) {
 			// Iterate over a copy to allow for init methods which in turn register new bean definitions.
 			// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
 			beanNames = new ArrayList<String>(this.beanDefinitionNames);
 		}
+
+		// Trigger initialization of all non-lazy singleton beans...
 		for (String beanName : beanNames) {
 			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
 			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
@@ -717,6 +721,26 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 				}
 			}
 		}
+
+		// Trigger post-initialization callback for all applicable beans...
+		for (String beanName : beanNames) {
+			Object singletonInstance = getSingleton(beanName);
+			if (singletonInstance instanceof SmartInitializingSingleton) {
+				final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
+				if (System.getSecurityManager() != null) {
+					AccessController.doPrivileged(new PrivilegedAction<Object>() {
+						@Override
+						public Object run() {
+							smartSingleton.afterSingletonsInstantiated();
+							return null;
+						}
+					}, getAccessControlContext());
+				}
+				else {
+					smartSingleton.afterSingletonsInstantiated();
+				}
+			}
+		}
 	}