BeanPostProcessor也称为Bean后置处理器，它是Spring中定义的接口，在Spring容器的创建过程中（具体为Bean初始化前后）会回调BeanPostProcessor中定义的两BeanPostProcessor.postProcessBeforeInitialization 以及 BeanPostProcessor.postProcessAfterInitialization

* BeanPostProcessor.postProcessBeforeInitialization
* 初始化：
* 对象创建完成，并赋值好，调用初始化方法。。。
* BeanPostProcessor.postProcessAfterInitialization
* 销毁：
* 单实例：容器关闭的时候
* 多实例：容器不会管理这个bean；容器不会调用销毁方法；
*
* 遍历得到容器中所有的BeanPostProcessor；挨个执行beforeInitialization，
* 一但返回null，跳出for循环，不会执行后面的BeanPostProcessor.postProcessorsBeforeInitialization

* BeanPostProcessor原理
* populateBean(beanName, mbd, instanceWrapper);给bean进行属性赋值
* initializeBean
* {
* applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
* invokeInitMethods(beanName, wrappedBean, mbd);执行自定义初始化
* applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);

/*
后置处理器,初始化前后进行处理工作
将后置处理器加入到容器中*/
public class MyBeanPostProcessor implements BeanPostProcessor {@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.println("postProcessBeforeInitialization.."+bean+".."+beanName);return bean;}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {System.out.println("postProcessAfterInitialization.."+bean+".."+beanName);return bean;}
}

public class App {public static void main(String[] args) {AnnotationConfigApplicationContext context=new AnnotationConfigApplicationContext(Config1.class);String[] beanDefinitionNames = context.getBeanDefinitionNames();for (String n:beanDefinitionNames){System.out.println(n);}context.close();}
}

运行结果：

dog construct......
postProcessBeforeInitialization..com.yuan.beancycle.model.Dog@5f8e8a9d..com.yuan.beancycle.model.Dog
dog init @PostConstruct .....
postProcessAfterInitialization..com.yuan.beancycle.model.Dog@5f8e8a9d..com.yuan.beancycle.model.Dog
16:04:41.709 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'car'
Car Constructor.....
postProcessBeforeInitialization..com.yuan.beancycle.model.Car@79207381..car
Car init .....
postProcessAfterInitialization..com.yuan.beancycle.model.Car@79207381..car
16:04:42.585 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'cat'
Cat 构造方法 。。。。。。
postProcessBeforeInitialization..com.yuan.beancycle.model.Cat@782859e..cat
Cat 初始化方法 。。。。。。
postProcessAfterInitialization..com.yuan.beancycle.model.Cat@782859e..cat
org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
config1
com.yuan.beancycle.model.Dog
com.yuan.beancycle.model.MyBeanPostProcessor
car
cat
16:04:43.236 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@544a2ea6, started on Mon Aug 05 15:52:34 CST 2019
Cat 销毁方法
Car destory .....
dog destory @PreDestroy .....