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Spring Framework example source code file (AbstractFactoryBean.java)

This example Spring Framework source code file (AbstractFactoryBean.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Spring Framework tags/keywords

abstractfactorybean, beanfactory, beanfactory, class, class, configurablebeanfactory, disposablebean, exception, exception, illegalstateexception, initializingbean, invocationhandler, object, object, reflection

The Spring Framework AbstractFactoryBean.java source code

/*
 * Copyright 2002-2007 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.config;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.SimpleTypeConverter;
import org.springframework.beans.TypeConverter;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.FactoryBeanNotInitializedException;
import org.springframework.beans.factory.InitializingBean;

/**
 * Simple template superclass for {@link FactoryBean} implementations that
 * creates a singleton or a prototype object, depending on a flag.
 *
 * <p>If the "singleton" flag is true (the default),
 * this class will create the object that it creates exactly once
 * on initialization and subsequently return said singleton instance
 * on all calls to the {@link #getObject()} method.
 * 
 * <p>Else, this class will create a new instance every time the
 * {@link #getObject()} method is invoked. Subclasses are responsible
 * for implementing the abstract {@link #createInstance()} template
 * method to actually create the object(s) to expose.
 *
 * @author Juergen Hoeller
 * @author Keith Donald
 * @since 1.0.2
 * @see #setSingleton(boolean)
 * @see #createInstance()
 */
public abstract class AbstractFactoryBean
		implements FactoryBean, BeanFactoryAware, InitializingBean, DisposableBean {

	/** Logger available to subclasses */
	protected final Log logger = LogFactory.getLog(getClass());

	private boolean singleton = true;

	private BeanFactory beanFactory;

	private boolean initialized = false;

	private Object singletonInstance;

	private Object earlySingletonInstance;


	/**
	 * Set if a singleton should be created, or a new object
	 * on each request else. Default is <code>true  (a singleton).
	 */
	public void setSingleton(boolean singleton) {
		this.singleton = singleton;
	}

	public boolean isSingleton() {
		return this.singleton;
	}

	public void setBeanFactory(BeanFactory beanFactory) {
		this.beanFactory = beanFactory;
	}

	/**
	 * Return the BeanFactory that this bean runs in.
	 */
	protected BeanFactory getBeanFactory() {
		return this.beanFactory;
	}

	/**
	 * Obtain a bean type converter from the BeanFactory that this bean
	 * runs in. This is typically a fresh instance for each call,
	 * since TypeConverters are usually <i>not thread-safe.
	 * <p>Falls back to a SimpleTypeConverter when not running in a BeanFactory.
	 * @see ConfigurableBeanFactory#getTypeConverter()
	 * @see org.springframework.beans.SimpleTypeConverter
	 */
	protected TypeConverter getBeanTypeConverter() {
		BeanFactory beanFactory = getBeanFactory();
		if (beanFactory instanceof ConfigurableBeanFactory) {
			return ((ConfigurableBeanFactory) beanFactory).getTypeConverter();
		}
		else {
			return new SimpleTypeConverter();
		}
	}

	/**
	 * Eagerly create the singleton instance, if necessary.
	 */
	public void afterPropertiesSet() throws Exception {
		if (isSingleton()) {
			this.initialized = true;
			this.singletonInstance = createInstance();
			this.earlySingletonInstance = null;
		}
	}


	/**
	 * Expose the singleton instance or create a new prototype instance.
	 * @see #createInstance()
	 * @see #getEarlySingletonInterfaces()
	 */
	public final Object getObject() throws Exception {
		if (isSingleton()) {
			return (this.initialized ? this.singletonInstance : getEarlySingletonInstance());
		}
		else {
			return createInstance();
		}
	}

	/**
	 * Determine an 'eager singleton' instance, exposed in case of a
	 * circular reference. Not called in a non-circular scenario.
	 */
	private Object getEarlySingletonInstance() throws Exception {
		Class[] ifcs = getEarlySingletonInterfaces();
		if (ifcs == null) {
			throw new FactoryBeanNotInitializedException(
					getClass().getName() + " does not support circular references");
		}
		if (this.earlySingletonInstance == null) {
			this.earlySingletonInstance = Proxy.newProxyInstance(getClass().getClassLoader(), ifcs,
				new InvocationHandler() {
					public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
						try {
							return method.invoke(getSingletonInstance(), args);
						}
						catch (InvocationTargetException ex) {
							throw ex.getTargetException();
						}
					}
				});
		}
		return this.earlySingletonInstance;
	}

	/**
	 * Expose the singleton instance (for access through the 'early singleton' proxy).
	 * @return the singleton instance that this FactoryBean holds
	 * @throws IllegalStateException if the singleton instance is not initialized
	 */
	private Object getSingletonInstance() throws IllegalStateException {
		if (!this.initialized) {
			throw new IllegalStateException("Singleton instance not initialized yet");
		}
		return this.singletonInstance;
	}

	/**
	 * Destroy the singleton instance, if any.
	 * @see #destroyInstance(Object)
	 */
	public void destroy() throws Exception {
		if (isSingleton()) {
			destroyInstance(this.singletonInstance);
		}
	}


	/**
	 * This abstract method declaration mirrors the method in the FactoryBean
	 * interface, for a consistent offering of abstract template methods.
	 * @see org.springframework.beans.factory.FactoryBean#getObjectType()
	 */
	public abstract Class getObjectType();

	/**
	 * Template method that subclasses must override to construct
	 * the object returned by this factory.
	 * <p>Invoked on initialization of this FactoryBean in case of
	 * a singleton; else, on each {@link #getObject()} call.
	 * @return the object returned by this factory
	 * @throws Exception if an exception occured during object creation
	 * @see #getObject()
	 */
	protected abstract Object createInstance() throws Exception;

	/**
	 * Return an array of interfaces that a singleton object exposed by this
	 * FactoryBean is supposed to implement, for use with an 'early singleton
	 * proxy' that will be exposed in case of a circular reference.
	 * <p>The default implementation returns this FactoryBean's object type,
	 * provided that it is an interface, or <code>null else. The latter
	 * indicates that early singleton access is not supported by this FactoryBean.
	 * This will lead to a FactoryBeanNotInitializedException getting thrown.
	 * @return the interfaces to use for 'early singletons',
	 * or <code>null to indicate a FactoryBeanNotInitializedException
	 * @see org.springframework.beans.factory.FactoryBeanNotInitializedException
	 */
	protected Class[] getEarlySingletonInterfaces() {
		Class type = getObjectType();
		return (type != null && type.isInterface() ? new Class[] {type} : null);
	}

	/**
	 * Callback for destroying a singleton instance. Subclasses may
	 * override this to destroy the previously created instance.
	 * <p>The default implementation is empty.
	 * @param instance the singleton instance, as returned by
	 * {@link #createInstance()}
	 * @throws Exception in case of shutdown errors
	 * @see #createInstance()
	 */
	protected void destroyInstance(Object instance) throws Exception {
	}

}

Other Spring Framework examples (source code examples)

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