/*
* Copyright 2002-2010 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.BeanClassLoaderAware;
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;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.util.ReflectionUtils;
/**
* 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 <code>true</code> (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
* @see #createInstance()
*/
public abstract class AbstractFactoryBean<T>
implements FactoryBean<T>, BeanClassLoaderAware, BeanFactoryAware, InitializingBean, DisposableBean {
/** Logger available to subclasses */
protected final Log logger = LogFactory.getLog(getClass());
private boolean singleton = true;
private ClassLoader beanClassLoader = ClassUtils.getDefaultClassLoader();
private BeanFactory beanFactory;
private boolean initialized = false;
private T singletonInstance;
private T earlySingletonInstance;
/**
* Set if a singleton should be created, or a new object on each request
* otherwise. Default is <code>true</code> (a singleton).
*/
public void setSingleton(boolean singleton) {
this.singleton = singleton;
}
public boolean isSingleton() {
return this.singleton;
}
public void setBeanClassLoader(ClassLoader classLoader) {
this.beanClassLoader = classLoader;
}
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</i> 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 T 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.
*/
@SuppressWarnings("unchecked")
private T 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 = (T) Proxy.newProxyInstance(
this.beanClassLoader, ifcs, new EarlySingletonInvocationHandler());
}
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 T 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 T 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</code> 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</code> 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(T instance) throws Exception {
}
/**
* Reflective InvocationHandler for lazy access to the actual singleton object.
*/
private class EarlySingletonInvocationHandler implements InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (ReflectionUtils.isEqualsMethod(method)) {
// Only consider equal when proxies are identical.
return (proxy == args[0]);
}
else if (ReflectionUtils.isHashCodeMethod(method)) {
// Use hashCode of reference proxy.
return System.identityHashCode(proxy);
}
else if (!initialized && ReflectionUtils.isToStringMethod(method)) {
return "Early singleton proxy for interfaces " +
ObjectUtils.nullSafeToString(getEarlySingletonInterfaces());
}
try {
return method.invoke(getSingletonInstance(), args);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}
}
}