BeanFactory和FactoryBean

 

1、 BeanFactory

    BeanFactory定义了 IOC 容器的最基本形式，并提供了 IOC 容器应遵守的的最基本的接口，也就是 Spring IOC所遵守的最底层和最基本的编程规范。在  Spring 代码中， BeanFactory 只是个接口，并不是 IOC 容器的具体实现，但是 Spring 容器给出了很多种实现，如 DefaultListableBeanFactory 、 XmlBeanFactory 、ApplicationContext 等，都是附加了某种功能的实现。

 

 

2、 FactoryBean

FactoryBean接口是插入到Spring IoC容器用来定制实例化逻辑的一个接口点。如果你有一些复杂的初始化代码用Java可以更好来表示，而不是用(可能)冗长的XML，那么你就可以创建你自己的FactoryBean，并在那个类中写入复杂的初始化动作，然后把你定制的FactoryBean插入容器中。 

FactoryBean接口对于 Spring 框架来说占用重要的地位， Spring 自身就提供了 70 多个 FactoryBean 的实现。它们隐藏了实例化一些复杂 Bean 的细节，给上层应用带来了便利。从 Spring 3.0 开始， FactoryBean 开始支持泛型，即接口声明改为 FactoryBean<T> 的形式：

 

在该接口中还定义了以下3 个方法：

T getObject()：返回由 FactoryBean 创建的 Bean 实例，如果 isSingleton() 返回 true ，则该实例会放到Spring 容器中单实例缓存池中；

boolean isSingleton()：返回由 FactoryBean 创建的 Bean 实例的作用域是 singleton 还是 prototype ；

Class<T> getObjectType()：返回 FactoryBean 创建的 Bean 类型。

 

当配置文件中<bean> 的 class 属性配置的实现类是 FactoryBean 时，通过 getBean() 方法返回的不是FactoryBean 本身，而是 FactoryBean#getObject() 方法所返回的对象，相当于 FactoryBean#getObject() 代理了 getBean() 方法。如果希望获取 FactoryBean 的实例，则需要在使用 getBean(beanName) 方法时在 beanName 前显示的加上 "&" 前缀：如 getBean("&beanName");

 

AbstractBeanFactory的getBean方法如下

 

public Object getBean(String name) throws BeansException {
		return getBean(name, null, null);
	}

public Object getBean(String name, Class requiredType, Object[] args) throws BeansException {
		return doGetBean(name, requiredType, args, false);
	}

protected Object doGetBean(
			final String name, final Class requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException {

		final String beanName = transformedBeanName(name);
		Object bean = null;

		// Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = getSingleton(beanName);
		if (sharedInstance != null && args == null) {
			if (logger.isDebugEnabled()) {
				if (isSingletonCurrentlyInCreation(beanName)) {
					logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
							"' that is not fully initialized yet - a consequence of a circular reference");
				}
				else {
					logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
				}
			}
			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		}

		else {
			// Fail if we're already creating this bean instance:
			// We're assumably within a circular reference.
			if (isPrototypeCurrentlyInCreation(beanName)) {
				throw new BeanCurrentlyInCreationException(beanName);
			}

			// Check if bean definition exists in this factory.
			BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// Not found -> check parent.
				String nameToLookup = originalBeanName(name);
				if (args != null) {
					// Delegation to parent with explicit args.
					return parentBeanFactory.getBean(nameToLookup, args);
				}
				else {
					// No args -> delegate to standard getBean method.
					return parentBeanFactory.getBean(nameToLookup, requiredType);
				}
			}

			if (!typeCheckOnly) {
				markBeanAsCreated(beanName);
			}

			final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
			checkMergedBeanDefinition(mbd, beanName, args);

			// Guarantee initialization of beans that the current bean depends on.
			String[] dependsOn = mbd.getDependsOn();
			if (dependsOn != null) {
				for (int i = 0; i < dependsOn.length; i++) {
					String dependsOnBean = dependsOn[i];
					getBean(dependsOnBean);
					registerDependentBean(dependsOnBean, beanName);
				}
			}

			// Create bean instance.
			if (mbd.isSingleton()) {
				sharedInstance = getSingleton(beanName, new ObjectFactory() {
					public Object getObject() throws BeansException {
						try {
							return createBean(beanName, mbd, args);
						}
						catch (BeansException ex) {
							// Explicitly remove instance from singleton cache: It might have been put there
							// eagerly by the creation process, to allow for circular reference resolution.
							// Also remove any beans that received a temporary reference to the bean.
							destroySingleton(beanName);
							throw ex;
						}
					}
				});
				bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
			}

			else if (mbd.isPrototype()) {
				// It's a prototype -> create a new instance.
				Object prototypeInstance = null;
				try {
					beforePrototypeCreation(beanName);
					prototypeInstance = createBean(beanName, mbd, args);
				}
				finally {
					afterPrototypeCreation(beanName);
				}
				bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
			}

			else {
				String scopeName = mbd.getScope();
				final Scope scope = (Scope) this.scopes.get(scopeName);
				if (scope == null) {
					throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
				}
				try {
					Object scopedInstance = scope.get(beanName, new ObjectFactory() {
						public Object getObject() throws BeansException {
							beforePrototypeCreation(beanName);
							try {
								return createBean(beanName, mbd, args);
							}
							finally {
								afterPrototypeCreation(beanName);
							}
						}
					});
					bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
				}
				catch (IllegalStateException ex) {
					throw new BeanCreationException(beanName,
							"Scope '" + scopeName + "' is not active for the current thread; " +
							"consider defining a scoped proxy for this bean if you intend to refer to it from a singleton",
							ex);
				}
			}
		}

		// Check if required type matches the type of the actual bean instance.
		if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
			throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
		}
		return bean;
	}

 

AbstractBeanFactory的getObjectForBeanInstance方法如下:

 

protected Object getObjectForBeanInstance(
			Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {

		// Don't let calling code try to dereference the factory if the bean isn't a factory.
		if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
			throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
		}

		// Now we have the bean instance, which may be a normal bean or a FactoryBean.
		// If it's a FactoryBean, we use it to create a bean instance, unless the
		// caller actually wants a reference to the factory.
		if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
			return beanInstance;
		}

		Object object = null;
		if (mbd == null) {
			object = getCachedObjectForFactoryBean(beanName);
		}
		if (object == null) {
			// Return bean instance from factory.
			FactoryBean factory = (FactoryBean) beanInstance;
			// Caches object obtained from FactoryBean if it is a singleton.
			if (mbd == null && containsBeanDefinition(beanName)) {
				mbd = getMergedLocalBeanDefinition(beanName);
			}
			boolean synthetic = (mbd != null && mbd.isSynthetic());
			object = getObjectFromFactoryBean(factory, beanName, !synthetic);
		}
		return object;
	}

 

 其中getObjectFromFactoryBean(factory, beanName, !synthetic)方法如下:

 

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);
		}
	}

 

 其中doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess)方法如下:

 

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);
	}

    由此可见如果spring中的Bean实现了FactoryBean，那么AbstractBeanFactory的getBean方法返回的是FactoryBean的getObject()方法返回的对象。

 

3、 实例

如JndiObjectFactoryBean：public class JndiObjectFactoryBean extends JndiObjectLocator implements FactoryBean, BeanClassLoaderAware {

	private Class[] proxyInterfaces;

	private boolean lookupOnStartup = true;

	private boolean cache = true;

	private boolean exposeAccessContext = false;

	private Object defaultObject;

	private ClassLoader beanClassLoader = ClassUtils.getDefaultClassLoader();

	private Object jndiObject;


....


/**
	 * Return the singleton JNDI object.
	 */
	public Object getObject() {
		return this.jndiObject;
	}

。。。。

public void afterPropertiesSet() throws IllegalArgumentException, NamingException {
		super.afterPropertiesSet();

		if (this.proxyInterfaces != null || !this.lookupOnStartup || !this.cache || this.exposeAccessContext) {
			// We need to create a proxy for this...
			if (this.defaultObject != null) {
				throw new IllegalArgumentException(
						"'defaultObject' is not supported in combination with 'proxyInterface'");
			}
			// We need a proxy and a JndiObjectTargetSource.
			this.jndiObject = JndiObjectProxyFactory.createJndiObjectProxy(this);
		}
		else {
			if (this.defaultObject != null && getExpectedType() != null &&
					!getExpectedType().isInstance(this.defaultObject)) {
				throw new IllegalArgumentException("Default object [" + this.defaultObject +
						"] of type [" + this.defaultObject.getClass().getName() +
						"] is not of expected type [" + getExpectedType().getName() + "]");
			}
			// Locate specified JNDI object.
			this.jndiObject = lookupWithFallback();
		}
	}

 

其中getObect()方法返回

this.jndiObject = JndiObjectProxyFactory.createJndiObjectProxy(this);产生的对象。该法法如下：

private static class JndiObjectProxyFactory {

		private static Object createJndiObjectProxy(JndiObjectFactoryBean jof) throws NamingException {
			// Create a JndiObjectTargetSource that mirrors the JndiObjectFactoryBean's configuration.
			JndiObjectTargetSource targetSource = new JndiObjectTargetSource();
			targetSource.setJndiTemplate(jof.getJndiTemplate());
			targetSource.setJndiName(jof.getJndiName());
			targetSource.setExpectedType(jof.getExpectedType());
			targetSource.setResourceRef(jof.isResourceRef());
			targetSource.setLookupOnStartup(jof.lookupOnStartup);
			targetSource.setCache(jof.cache);
			targetSource.afterPropertiesSet();

			// Create a proxy with JndiObjectFactoryBean's proxy interface and the JndiObjectTargetSource.
			ProxyFactory proxyFactory = new ProxyFactory();
			if (jof.proxyInterfaces != null) {
				proxyFactory.setInterfaces(jof.proxyInterfaces);
			}
			else {
				Class targetClass = targetSource.getTargetClass();
				if (targetClass == null) {
					throw new IllegalStateException(
							"Cannot deactivate 'lookupOnStartup' without specifying a 'proxyInterface' or 'expectedType'");
				}
				proxyFactory.setInterfaces(ClassUtils.getAllInterfacesForClass(targetClass, jof.beanClassLoader));
			}
			if (jof.exposeAccessContext) {
				proxyFactory.addAdvice(new JndiContextExposingInterceptor(jof.getJndiTemplate()));
			}
			proxyFactory.setTargetSource(targetSource);
			return proxyFactory.getProxy(jof.beanClassLoader);
		}
	}

 

对应的sping配置文件如下：

<bean id="dataSource" class="org.springframework.jndi.JndiObjectFactoryBean">
		<property name="jndiName">
			<value>java:LpscmDS</value>
		</property>
		<property name="jndiTemplate">
			<ref local="jndiTemplate" />
		</property>
		<property name="defaultObject">
			<ref local="dbcpDataSource" />
		</property>
	</bean>
	

 

4、 区别

    BeanFactory是个 Factory ，也就是 IOC 容器或对象工厂， FactoryBean 是个 Bean 。在 Spring 中，所有的Bean 都是由 BeanFactory( 也就是 IOC 容器 ) 来进行管理的。但对 FactoryBean 而言，这个 Bean 不是简单的Bean ，而是一个能生产或者修饰对象生成的工厂 Bean, 它的实现与设计模式中的工厂模式和修饰器模式类似。