Spring源码分析(六)FactoryBean 接口解析

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说道FactoryBean,不少人会拿它跟BeanFactory作比较,但是实际上他们没有多大关系;我们简单介绍一下两者

一、BeanFactory和FactoryBean区别

BeanFactory


BeanFactory:这就是一个Factory,是一个IOC容器或者叫对象工厂,它里面存着很多的bean。例如默认的实现方式DefaultListableBeanFactory;我们把IOC容器可以比作一个水桶,IOC容器里面的所有bean就是装的水; ##FactoryBean


FactoryBean:是一个Java Bean,但是它是一个能生产对象的工厂Bean,把IOC容器比作水桶,那么Java Bean就是水桶里面的水,但是这个FactoryBean一种比较特殊的水,可以把它看成是一个水球,这个水球里面也包含了水,我们可以通过IOC取这个水球,但是也可以直接取水球里面的水;(用法就是 用&表示取水球,取水球里的水用正常的获取方式就行了;如果我们用&获取到了水球之后,可以通过这个水球的 getObject方法获取水球里面的水;)

在之前的文章中我们已经分析过BeanFactory的源码了,今天我们单独分析FactoryBean

代码入口


  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);
    }

AbstractBeanFactory

AbstractBeanFactory extends FactoryBeanRegistrySupport

断点进去最后访问到AbstractBeanFactory的getObjectForBeanInstance方法;方法中的几个参数分别表示 beanInstance: 通过Object sharedInstance = getSingleton(beanName);获取到的,这个就是实例化的对象,就算用我们getBean的时候beanName传的是fb,不是&fb,这里返回的就是FactoryBean的实例对象;就是上面比喻的水球; name:就是传进来的name ;没有过滤&字符的; beanName:过滤了&字符的

	/**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;
	}


FactoryBeanRegistrySupport

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;
	}

二、总结

总结一下整个FactoryBean源码的流程 1.判断是否需要调用FactoryBean的getObject方法来获取实例 判断依据是:①.如果name有前缀&,直接返回 ②.如果没有前缀&,调用getObject方法获取实例 2.如果是通过调用GetObject方法获取实例,则还要执行一下后置处理器 执行后置处理器接口的方法BeanPostProcessor中的 postProcessAfterInitialization(result, beanName);方法;

三、分析过程有一些需要单独分析,占个坑


1. mbd.isSynthetic()中的值是什么时候设置的?有什么用?

TODO...

2.BeanPostProcessor后置处理器讲解

BeanPostProcessor解析

3.上面Object alreadyThere = this.factoryBeanObjectCache.get(beanName);这段代码的意思?什么情况下要先查这个?

TODO.....

说明文字

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