Spring源码分析-IOC之FactoryBeanRegistrySupport

       上一篇Spring源码分析-IOC之FactoryBean我们介绍了FactoryBean的使用,以及在ioc中的实现原理,其中实现原理中我们可以发现最终是调用的FactoryBeanRegistrySupport的getObjectFromFactoryBean和doGetObjectFromFactoryBean这个方法。

        FactoryBeanRegistrySupport主要是在DefaultSingletonBeanRegistry基础上增加了对FactoryBean的特殊处理功能,下面我们来看下具体的源码:

public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanRegistry {

	//缓存factoryBeans创建的singletong对象
	private final Map<String, Object> factoryBeanObjectCache = new ConcurrentHashMap<String, Object>(16);


	//获取指定factoryBean中实例化对象的类型
	protected Class<?> getTypeForFactoryBean(final FactoryBean<?> factoryBean) {
		try {
            //此处是JDK的权限控制,主要是操作系统层面的权限
            //我们开发中很少用到
			if (System.getSecurityManager() != null) {
				return AccessController.doPrivileged(new PrivilegedAction<Class<?>>() {
					@Override
					public Class<?> run() {
						return factoryBean.getObjectType();
					}
				}, getAccessControlContext());
			}
			else {
				return factoryBean.getObjectType();
			}
		}
		catch (Throwable ex) {
			return null;
		}
	}

	//从缓存中获取指定的beanName的对象如果是NULL_OBJECT则返回null
	protected Object getCachedObjectForFactoryBean(String beanName) {
		Object object = this.factoryBeanObjectCache.get(beanName);
		return (object != NULL_OBJECT ? object : null);
	}

	//从指定的FactoryBean中获得给定beanName的实例对象
	protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
           //判断工厂是否是单例,以及单例缓存中是否有beanName
		if (factory.isSingleton() && containsSingleton(beanName)) {
            //单例缓存加上同步快防止并发
			synchronized (getSingletonMutex()) {
                //判断factoryBean中是否有指定的beanName
				Object object = this.factoryBeanObjectCache.get(beanName);
				if (object == null) {
                    //如果缓存中没有,通过factoryBean获取对象
					object = doGetObjectFromFactoryBean(factory, beanName);
					//再次从缓存中获取对象
                    //如果存在则赋值给object对象
					Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
					if (alreadyThere != null) {
						object = alreadyThere;
					}
                    //不存在的话则获取,并存放到缓存池中
					else {
						if (object != null && shouldPostProcess) {
							try {
                                //此获取对象的方法一般有子类实现
								object = postProcessObjectFromFactoryBean(object, beanName);
							}
							catch (Throwable ex) {
								throw new BeanCreationException(beanName,
										"Post-processing of FactoryBean's singleton object failed", ex);
							}
						}
                           //将对象存放到缓存中
						this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
					}
				}
                //返回对象,如果是空对象的话则返回null
				return (object != NULL_OBJECT ? object : null);
			}
		}
		else {
            //通过factoryBean获取对象
			Object object = doGetObjectFromFactoryBean(factory, beanName);
			if (object != null && shouldPostProcess) {
				try {
                     //此获取对象的方法一般有子类实现
					object = postProcessObjectFromFactoryBean(object, beanName);
				}
				catch (Throwable ex) {
					throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
				}
			}
            //返回对象
			return object;
		}
	}

	//通过factoryBean获取对象
	private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)
			throws BeanCreationException {

		Object object;
		try {
               //此处是JDK的权限控制,主要是操作系统层面的权限
            //我们开发中很少用到
			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 {
                //factoryBean直接获取对象,上一篇我们可以看到具体入口,怎么一步步进来
				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);
		}

		// 不允许对象为空,或者正在创建
		if (object == null && isSingletonCurrentlyInCreation(beanName)) {
			throw new BeanCurrentlyInCreationException(
					beanName, "FactoryBean which is currently in creation returned null from getObject");
		}
		return object;
	}

	//此方法一般由子类重写
	protected Object postProcessObjectFromFactoryBean(Object object, String beanName) throws BeansException {
		return object;
	}

	//获取指定名称的factoryBean,如果该实例是factoryBean的话,否则报错
	protected FactoryBean<?> getFactoryBean(String beanName, Object beanInstance) throws BeansException {
		if (!(beanInstance instanceof FactoryBean)) {
			throw new BeanCreationException(beanName,
					"Bean instance of type [" + beanInstance.getClass() + "] is not a FactoryBean");
		}
		return (FactoryBean<?>) beanInstance;
	}

	//移除指定的单例对象
	@Override
	protected void removeSingleton(String beanName) {
		super.removeSingleton(beanName);
		this.factoryBeanObjectCache.remove(beanName);
	}

	//权限管理,系统层面
	protected AccessControlContext getAccessControlContext() {
		return AccessController.getContext();
	}

}

以上就是FactoryBeanRegistrySupport的源代码,大家可以根据源码以及上一篇的例子分析,有什么问题可以给我留言.