Spring的BeanFactoryPostProcessor和BeanPostProcessor

PostProcessor：后处理器； 
BeanPostProcessor：Bean的后置处理器（处理的对象是Bean）； 
BeanFactoryPostProcessor：BeanFactory的后置处理器（处理的对象是BeanFactory）

（1）看一下BeanFactoryPostProcessor接口的源码：

@FunctionalInterface public interface BeanFactoryPostProcessor { /** * Modify the application context's internal bean factory after its standard * initialization. All bean definitions will have been loaded, but no beans * will have been instantiated yet. This allows for overriding or adding * properties even to eager-initializing beans. * @param beanFactory the bean factory used by the application context * @throws org.springframework.beans.BeansException in case of errors */ void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException; } 

 

①方法postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)的做用是什么？ 
源码中是这样说明的：

//Modify the application context's internal bean factory after its standard initialization.

bean factory已经经历了standard initialization； 
方法的入参ConfigurableListableBeanFactory beanFactory便是standard initialization后的bean factory； 
把standard initialization后的bean factory交给咱们处理，咱们能够对其进行修改。 
②何时调用postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)？ 
源码中是这样说明的：

// All bean definitions will have been loaded, but no beans will have been instantiated yet.

 

bean factory已经经历了standard initialization，全部的bean definitions也已经被加载到bean factory之中，可是尚未建立（实例化）任何的Bean。 
③方法的入参beanFactory 
方法的入参ConfigurableListableBeanFactory beanFactory便是咱们须要处理的对象；beanFactory已经经历了standard initialization，全部的bean definitions也已经被加载到beanFactory之中。 
④如何操做（处理）beanFactory呢？ 
操做beanFactory的常见方式： 
对加载到beanFactory中的bean definitions进行修改。

经过参数beanFactory，能够获取相关Bean的bean definition，并修改bean definition。

（2）代码示例： 
User类：

public class User { private String username; private int age; public void setUsername(String username) { System.out.println("setUsername()"); this.username = username; } public void setAge(int age) { System.out.println("setAge()"); this.age = age; } public User(){ System.out.println("Constructor()"); } @Override public String toString() { return "User [username=" + username + ", age=" + age + "]"; } }

BeanFactoryPostProcessor处理器：

public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor { public MyBeanFactoryPostProcessor(){ System.out.println("BeanFactoryPostProcessor实现类的构造器"); } @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { System.out.println("BeanFactoryPostProcessor.postProcessBeanFactory()"); //获取指定的BeanDefinition BeanDefinition bd = beanFactory.getBeanDefinition("user1"); //根据BeanDefinition获取MutablePropertyValues MutablePropertyValues pvs = bd.getPropertyValues(); //增长 pvs.add("age", 20); //覆盖 pvs.add("username", "Richard"); } } 

 

Bean配置文件：

<bean id="user1" class="com.User"> <!-- 这里只为属性username赋值，属性age没有赋值 --> <property name="username" value="Jack"></property> </bean> <bean class="com.MyBeanFactoryPostProcessor"></bean>

 

测试类：

public static void main(String[] args) { ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml"); User user1=(User)context.getBean("user1"); System.out.println(user1); } 

运行结果： 

BeanFactoryPostProcessor实现类的构造器 
BeanFactoryPostProcessor.postProcessBeanFactory() 
Constructor() 
setUsername() 
setAge() 
User [username=Richard, age=20]

（3）注意点： 
BeanFactoryPostProcessor接口和BeanPostProcessor接口很是类似，都是spring初始化bean时对外暴露的扩展点。

①BeanFactory的后置处理器：Spring提供的一种特殊的Bean 
②BeanFactory的后置处理器，须要实现BeanFactoryPostProcessor接口 
③须要在Bean的配置文件中，注册BeanFactory的后置处理器，但不须要设置id属性。IOC容器会自动识别这是个BeanFactory的后置处理器，自动的使用它。

<bean class="com.MyBeanFactoryPostProcessor"></bean>

 

④实例化BeanFactoryPostProcessor实现类，并调用BeanFactoryPostProcessor的postProcessBeanFactory()方法； 这2步会很早进行，在Bean实例被建立以前进行。 ⑤Bean的后置处理器，操做的对象是Bean，会对容器中的全部Bean进行处理，每一个Bean都要通过2个处理方法postProcessBeforeInitialization()和postProcessAfterInitialization()； BeanFactory的后置处理器，操做的对象是BeanFactory，所以只会有一次处理过程（很早进行，在Bean实例被建立以前进行），即只调用处理方法postProcessBeanFactory()一次。