spring SqlSessionFactoryBean创建SqlSessionFactory

原文地址：http://blog.youkuaiyun.com/wdyr321/article/details/11763979

Application.xml

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1. <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">  
2.   <property name="dataSource" ref="dataSource" />  
3.   <property name="configLocation" value="classpath:SQL_MAP_SERVICE_CONFIG.xml" />  
4. </bean>  

创建SqlSessionFactory

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1. ApplicationContext ctx = new ClassPathXmlApplicationContext("APPLICATION.xml");  
2. SqlSessionFactory sqlSessionFactory=(SqlSessionFactory) ctx.getBean("sqlSessionFactory");  

为什么返回的是SqlSessionFactory对象而不是SqlSessionFactoryBean
首先spring在初始化的时候会将所有创建的单例以Map<K,V>的形式放入singletonObjects，同时调用FactoryBean的getObject()将返回的对象以Map<K,V>的形式放入factoryBeanObjectCache

如{sqlSessionFactory=org.apache.ibatis.session.defaults.DefaultSqlSessionFactory@d997f9}

然后getBean的时候，spring利用getSingleton从singletonObjects获取单例(这里是SqlSessionFactoryBean对象)，判断是否实现了FactoryBean接口，若实现了就从factoryBeanObjectCache利用beanname(这里是sqlSessionFactory)重新获取，若未实现则返回getSingleton获取的单例

初始化的源码有些复杂，理不清，下面仅仅是getBean的源码：

1、首先调用的是ClassPathXmlApplicationContext父类AbstractRefreshableApplicationContext的父类AbstractApplicationContext的getBean()。

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1. public Object getBean(String name) throws BeansException {  
2.     return getBeanFactory().getBean(name);  
3. }  

2、调用AbstractRefreshableApplicationContext的getBeanFactory()返回ConfigurableListableBeanFactory接口实现类DefaultListableBeanFactory

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1.       
2. @Override(重写了AbstractApplicationContext的getBeanFactory抽象方法)  
3.     public final ConfigurableListableBeanFactory getBeanFactory() {  
4.         synchronized (this.beanFactoryMonitor) {  
5.             if (this.beanFactory == null) {  
6.                 throw new IllegalStateException("BeanFactory not initialized or already closed - " +  
7.                         "call 'refresh' before accessing beans via the ApplicationContext");  
8.             }  
9.             return this.beanFactory;  
10.         }  
11.     }  

3、调用DefaultListableBeanFactory的父类AbstractBeanFactory的geBean()

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1.       
2. public Object getBean(String name) throws BeansException {  
3.         return doGetBean(name, null, null, false);  
4.     }  

4、调用AbstractBeanFactory的doGetBean()

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1.       
2. protected  T doGetBean(  
3.             final String name, final Class requiredType, final Object[] args, boolean typeCheckOnly)  
4.             throws BeansException {  
5.   
6.         final String beanName = transformedBeanName(name);  
7.         Object bean;  
8.   
9.         // Eagerly check singleton cache for manually registered singletons.  
10.         Object sharedInstance = getSingleton(beanName);//根据bean路径获取单例  
11.         if (sharedInstance != null && args == null) {  
12.             if (logger.isDebugEnabled()) {  
13.                 if (isSingletonCurrentlyInCreation(beanName)) {  
14.                     logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +  
15.                             "' that is not fully initialized yet - a consequence of a circular reference");  
16.                 }  
17.                 else {  
18.                     logger.debug("Returning cached instance of singleton bean '" + beanName + "'");  
19.                 }  
20.             }  
21.             bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);  
22.         }  

5、调用AbstractBeanFactory的getObjectForBeanInstance()，判断是否实现FactoryBean接口，若未实现则返回上一步创建的单例

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1.       
2. protected Object getObjectForBeanInstance(  
3.             Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {  
4.   
5.         // Don't let calling code try to dereference the factory if the bean isn't a factory.  
6.         if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {  
7.             throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());  
8.         }  
9.   
10.         // Now we have the bean instance, which may be a normal bean or a FactoryBean.  
11.         // If it's a FactoryBean, we use it to create a bean instance, unless the  
12.         // caller actually wants a reference to the factory.  
13.         if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {  
14.             return beanInstance;  
15.         }//判断是否实现FactoryBean接口  
16.   
17.         Object object = null;  
18.         if (mbd == null) {  
19.             object = getCachedObjectForFactoryBean(beanName);//从factoryBeanObjectCache中取出FactoryBean创建的对象  
20.         }  
21.         if (object == null) {  
22.             // Return bean instance from factory.  
23.             FactoryBean factory = (FactoryBean) beanInstance;  
24.             // Caches object obtained from FactoryBean if it is a singleton.  
25.             if (mbd == null && containsBeanDefinition(beanName)) {  
26.                 mbd = getMergedLocalBeanDefinition(beanName);  
27.             }  
28.             boolean synthetic = (mbd != null && mbd.isSynthetic());  
29.             object = getObjectFromFactoryBean(factory, beanName, !synthetic);  
30.         }  
31.         return object;  
32.     }