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。