factorybeanregistrysupport.java

来自「spring framework 2.5.4源代码」· Java 代码 · 共 189 行

/*
 * Copyright 2002-2008 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.support;

import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Map;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanCreationException;
import org.springframework.beans.factory.BeanCurrentlyInCreationException;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.FactoryBeanNotInitializedException;
import org.springframework.core.CollectionFactory;

/**
 * Support base class for singleton registries which need to handle
 * {@link org.springframework.beans.factory.FactoryBean} instances,
 * integrated with {@link DefaultSingletonBeanRegistry}'s singleton management.
 *
 * <p>Serves as base class for {@link AbstractBeanFactory}.
 *
 * @author Juergen Hoeller
 * @since 2.5.1
 */
public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanRegistry {

	/** Cache of singleton objects created by FactoryBeans: FactoryBean name --> object */
	private final Map factoryBeanObjectCache = CollectionFactory.createConcurrentMapIfPossible(16);


	/**
	 * Determine the type for the given FactoryBean.
	 * @param factoryBean the FactoryBean instance to check
	 * @return the FactoryBean's object type,
	 * or <code>null</code> if the type cannot be determined yet
	 */
	protected Class getTypeForFactoryBean(FactoryBean factoryBean) {
		try {
			return factoryBean.getObjectType();
		}
		catch (Throwable ex) {
			// Thrown from the FactoryBean's getObjectType implementation.
			logger.warn("FactoryBean threw exception from getObjectType, despite the contract saying " +
					"that it should return null if the type of its object cannot be determined yet", ex);
			return null;
		}
	}

	/**
	 * Obtain an object to expose from the given FactoryBean, if available
	 * in cached form. Quick check for minimal synchronization.
	 * @param beanName the name of the bean
	 * @return the object obtained from the FactoryBean,
	 * or <code>null</code> if not available
	 */
	protected Object getCachedObjectForFactoryBean(String beanName) {
		Object object = this.factoryBeanObjectCache.get(beanName);
		return (object != NULL_OBJECT ? object : null);
	}

	/**
	 * Obtain an object to expose from the given FactoryBean.
	 * @param factory the FactoryBean instance
	 * @param beanName the name of the bean
	 * @param shouldPostProcess whether the bean is subject for post-processing
	 * @return the object obtained from the FactoryBean
	 * @throws BeanCreationException if FactoryBean object creation failed
	 * @see org.springframework.beans.factory.FactoryBean#getObject()
	 */
	protected Object getObjectFromFactoryBean(FactoryBean factory, String beanName, boolean shouldPostProcess) {
		if (factory.isSingleton() && containsSingleton(beanName)) {
			synchronized (getSingletonMutex()) {
				Object object = this.factoryBeanObjectCache.get(beanName);
				if (object == null) {
					object = doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
					this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
				}
				return (object != NULL_OBJECT ? object : null);
			}
		}
		else {
			return doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
		}
	}

	/**
	 * Obtain an object to expose from the given FactoryBean.
	 * @param factory the FactoryBean instance
	 * @param beanName the name of the bean
	 * @param shouldPostProcess whether the bean is subject for post-processing
	 * @return the object obtained from the FactoryBean
	 * @throws BeanCreationException if FactoryBean object creation failed
	 * @see org.springframework.beans.factory.FactoryBean#getObject()
	 */
	private Object doGetObjectFromFactoryBean(
			final FactoryBean factory, final String beanName, final boolean shouldPostProcess)
			throws BeanCreationException {

		AccessControlContext acc = AccessController.getContext();
		return AccessController.doPrivileged(new PrivilegedAction() {
			public Object run() {
				Object object;

				try {
					object = factory.getObject();
				}
				catch (FactoryBeanNotInitializedException ex) {
					throw new BeanCurrentlyInCreationException(beanName, ex.toString());
				}
				catch (Throwable ex) {
					throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
				}

				// Do not accept a null value for a FactoryBean that's not fully
				// initialized yet: Many FactoryBeans just return null then.
				if (object == null && isSingletonCurrentlyInCreation(beanName)) {
					throw new BeanCurrentlyInCreationException(
							beanName, "FactoryBean which is currently in creation returned null from getObject");
				}

				if (object != null && shouldPostProcess) {
					try {
						object = postProcessObjectFromFactoryBean(object, beanName);
					}
					catch (Throwable ex) {
						throw new BeanCreationException(beanName, "Post-processing of the FactoryBean's object failed", ex);
					}
				}

				return object;
			}
		}, acc);
	}

	/**
	 * Post-process the given object that has been obtained from the FactoryBean.
	 * The resulting object will get exposed for bean references.
	 * <p>The default implementation simply returns the given object as-is.
	 * Subclasses may override this, for example, to apply post-processors.
	 * @param object the object obtained from the FactoryBean.
	 * @param beanName the name of the bean
	 * @return the object to expose
	 * @throws org.springframework.beans.BeansException if any post-processing failed
	 */
	protected Object postProcessObjectFromFactoryBean(Object object, String beanName) throws BeansException {
		return object;
	}

	/**
	 * Get a FactoryBean for the given bean if possible.
	 * @param beanName the name of the bean
	 * @param beanInstance the corresponding bean instance
	 * @return the bean instance as FactoryBean
	 * @throws BeansException if the given bean cannot be exposed as a FactoryBean
	 */
	protected FactoryBean getFactoryBean(String beanName, Object beanInstance) throws BeansException {
		if (!(beanInstance instanceof FactoryBean)) {
			throw new BeanCreationException(beanName,
					"Bean instance of type [" + beanInstance.getClass() + "] is not a FactoryBean");
		}
		return (FactoryBean) beanInstance;
	}

	/**
	 * Overridden to clear the FactoryBean object cache as well.
	 */
	protected void removeSingleton(String beanName) {
		super.removeSingleton(beanName);
		this.factoryBeanObjectCache.remove(beanName);
	}

}