public static void main(String[] args){         ClassPathResource resource = new ClassPathResource("SpringContextConfig.xml");        DefaultListableBeanFactory factory = new DefaultListableBeanFactory();        XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);        reader.loadBeanDefinitions(resource);        MyFactoryBean beanA = (MyFactoryBean)factory.getBean("&fb");        TestFb beanB = (TestFb)factory.getBean("fb");        TestFb beanC =beanA.getObject();        System.out.print(beanB==beanC);        System.out.print(beanA);    }

 /**专门缓存从FactoryBeans中生成的对象的；除了第一次要getObject()，后面直接从这个mao中取就行了  Cache of singleton objects created by FactoryBeans: FactoryBean name --> object */ private final Map<String, Object> factoryBeanObjectCache = new ConcurrentHashMap<String, Object>(16);

protected Object getObjectForBeanInstance(   Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {
  // 如果name 是&开头的，但是beanInstance又不是FactoryBean类型的就抛出异常  if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {   throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());  }
    //如果不是FactoryBean 例如name=fb；直接返回  //如果name是&开头并且FactoryBean类型的例如name=&fb,fb也是FactoryBean类型； 直接返回  if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {   return beanInstance;  } // beanInstance是FactoryBean类型的并且name不是是以&开头的;例如name=fb 就要走下面的流程 //beanInstance不是FactoryBean类型并且name  Object object = null;  if (mbd == null) {  //检查之前是否已经生成放入缓存了，如果有 直接返回   object = getCachedObjectForFactoryBean(beanName);  }  if (object == null) {   // Return bean instance from factory.   FactoryBean<?> factory = (FactoryBean<?>) beanInstance;   // 获取合并之后的BeanDefinition   if (mbd == null && containsBeanDefinition(beanName)) {    mbd = getMergedLocalBeanDefinition(beanName);   }   //TODO....暂时不知道这里是怎么设置的，回头分析   boolean synthetic = (mbd != null && mbd.isSynthetic());   /**   *1.返回FactoryBean.getObject()对象   *2.执行后置处理器接口的方法BeanPostProcessor中的   *postProcessAfterInitialization(result, beanName);方法；   */   object = getObjectFromFactoryBean(factory, beanName, !synthetic);  }  return object; }

public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanRegistry{
 /**  * 从FactoryBean中获取Bean  * @param factory the FactoryBean instance  * @param beanName the name of the bean  * @param shouldPostProcess whether the bean is subject to 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) { //判断factory是单例的并且beanName已经被创建  if (factory.isSingleton() && containsSingleton(beanName)) {   synchronized (getSingletonMutex()) {   //如果已经创建过直接返回    Object object = this.factoryBeanObjectCache.get(beanName);    if (object == null) {     object = doGetObjectFromFactoryBean(factory, beanName);     // Only post-process and store if not put there already during getObject() call above     // (e.g. because of circular reference processing triggered by custom getBean calls)     //TODO....这里回头分析...     Object alreadyThere = this.factoryBeanObjectCache.get(beanName);     if (alreadyThere != null) {      object = alreadyThere;     }     else {      if (object != null && shouldPostProcess) {       try {       //执行所有后置处理器接口的方法BeanPostProcessor中的postProcessAfterInitialization(result, beanName);方法；       //这里单独写一篇文章将后置处理器BeanPostProcessor        object = postProcessObjectFromFactoryBean(object, beanName);       }       catch (Throwable ex) {        throw new BeanCreationException(beanName,          "Post-processing of FactoryBean's singleton object failed", ex);       }      } //将通过factoryBean.getObject方法得到的对象存到 factoryBeanObjectCache中   this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));     }    }    return (object != NULL_OBJECT ? object : null);   }  }  else {//如果不是单例对象  //调用FactoryBean的getObject方法返回实例，也就是从水球里面取出水；   Object object = doGetObjectFromFactoryBean(factory, beanName);   if (object != null && shouldPostProcess) {    try {    //执行后置处理器     object = postProcessObjectFromFactoryBean(object, beanName);    }    catch (Throwable ex) {     throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);    }   }   return object;  } }  //调用FactoryBean的getObject放法 private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)   throws BeanCreationException {
  Object object;  try {   if (System.getSecurityManager() != null) {    AccessControlContext acc = getAccessControlContext();    try {     object = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {      @Override      public Object run() throws Exception {        return factory.getObject();       }      }, acc);    }    catch (PrivilegedActionException pae) {     throw pae.getException();    }   }   else {    //可以看到最终调用了getObject方法；这是需要实现类自己实现    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");  }  return object; }