spring IoC （五）BeanPostProcessor

参考 Spring IoC （二）实例化、初始化

　　BeanPostProcessor是使用IoC容器时经常会遇到的一个特性，这个Bean的后置处理器是一个监听器，它

可以监听容器触发的事件。将它向IoC容器注册后，容器中管理的Bean具备了接受IoC容器事件回调的能力。

BeanPostProcessor接口

 1 public interface BeanPostProcessor {
 2 
 3     /**
 4      * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
 5      * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
 6      * or a custom init-method). The bean will already be populated with property values.
 7      * The returned bean instance may be a wrapper around the original.
 8      * @param bean the new bean instance
 9      * @param beanName the name of the bean
10      * @return the bean instance to use, either the original or a wrapped one; if
11      * {@code null}, no subsequent BeanPostProcessors will be invoked
12      * @throws org.springframework.beans.BeansException in case of errors
13      * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
14      */
15     Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
16 
17     /**
18      * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
19      * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
20      * or a custom init-method). The bean will already be populated with property values.
21      * The returned bean instance may be a wrapper around the original.
22      * <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
23      * instance and the objects created by the FactoryBean (as of Spring 2.0). The
24      * post-processor can decide whether to apply to either the FactoryBean or created
25      * objects or both through corresponding {@code bean instanceof FactoryBean} checks.
26      * <p>This callback will also be invoked after a short-circuiting triggered by a
27      * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
28      * in contrast to all other BeanPostProcessor callbacks.
29      * @param bean the new bean instance
30      * @param beanName the name of the bean
31      * @return the bean instance to use, either the original or a wrapped one; if
32      * {@code null}, no subsequent BeanPostProcessors will be invoked
33      * @throws org.springframework.beans.BeansException in case of errors
34      * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
35      * @see org.springframework.beans.factory.FactoryBean
36      */
37     Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
38 
39 }

流程图

通过populateBean方法和 initializeBean调用