spring 后置处理器BeanFactoryPostProcessor和BeanPostProcessor的用法和区别

主要区别就是：BeanFactoryPostProcessor(BeanFactory的后置处理器)可以修改BEAN的配置信息而BeanPostProcessor(Bean的后置处理器)不能:

package com.springdemo.postProcessor;  
  
public class PostProcessorBean {  
    private String username;  
      
    private String password;  
  
    public String getPassword() {  
        return password;  
    }  
  
    public void setPassword(String password) {  
        this.password = password;  
    }  
  
    public String getUsername() {  
        return username;  
    }  
  
    public void setUsername(String username) {  
        this.username = username;  
    }  
}

MyBeanPostProcessor类，实现了BeanPostProcessor接口:

package com.springdemo.postProcessor;  
  
import org.springframework.beans.BeansException;  
import org.springframework.beans.factory.config.BeanPostProcessor;  
  
import com.springdemo.form.LoginForm;  
  
public class MyBeanPostProcessor implements BeanPostProcessor {  
  
      
      
    public Object postProcessAfterInitialization(Object bean, String beanName)  
            throws BeansException {  
        //如果是PostProcessorBean则username信息  
        if(bean instanceof PostProcessorBean)  
        {  
            System.out.println("PostProcessorBean Bean initialized");  
            PostProcessorBean pb = (PostProcessorBean)bean;  
              
            System.out.println("username:"+pb.getUsername());  
        }  
        return bean;  
    }  
  
    public Object postProcessBeforeInitialization(Object bean, String beanName)  
            throws BeansException {  
         if(bean instanceof PostProcessorBean)  
        {  
            System.out.println("PostProcessorBean Bean initializing");  
            PostProcessorBean pb = (PostProcessorBean)bean;  
              
            System.out.println("username:"+pb.getUsername());  
        }  
        return bean;  
    }  
  
}

MyBeanFactoryPostProcessor实现了BeanFactoryPostProcessor接口:

package com.springdemo.postProcessor;  
  
import org.springframework.beans.BeansException;  
import org.springframework.beans.MutablePropertyValues;  
import org.springframework.beans.factory.config.BeanDefinition;  
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;  
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;  
  
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {  
  
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)  
            throws BeansException {  
        
        //BeanFactoryPostProcessor可以修改BEAN的配置信息而BeanPostProcessor不能  
        //在这里修改postProcessorBean的username注入属性  
        BeanDefinition bd = beanFactory.getBeanDefinition("postProcessorBean");  
        MutablePropertyValues pv =  bd.getPropertyValues();  
        if(pv.contains("username"))  
        {  
            pv.addPropertyValue("username", "xiaojun");  
        }  
          
    }  
  
}

编写测试用例：

package com.springdemo.test;  
  
  
import org.springframework.context.ApplicationContext;  
import org.springframework.context.support.ClassPathXmlApplicationContext;  
  
import com.springdemo.factory.ApplicationContextFactory;  
  
import com.springdemo.postProcessor.PostProcessorBean;  
  
import junit.framework.TestCase;  
  
public class BeanPostPorcessorTest extends TestCase {  
    private ApplicationContext context;  
    protected void setUp() throws Exception {  
        super.setUp();  
        String[] paths = {"classpath*:/spring/applicationContext-*.xml"};  
  
        context = new ClassPathXmlApplicationContext(paths);  
          
    }  
  
    protected void tearDown() throws Exception {  
        super.tearDown();  
    }  
      
    public void testBeanPostProcessor()  
    {  
          
    }  
    public void testBeanFactoryPostProcessor()  
    {  
        PostProcessorBean bean =(PostProcessorBean)context.getBean("postProcessorBean");  
        System.out.println("---------------testBeanFactoryPostProcessor----------------");  
        System.out.println("username:"+bean.getUsername());  
        System.out.println("password:"+bean.getPassword());    
    }  
}

spring配置文件如下（先不启用MyBeanFactoryPostProcessor）：

<?xml version="1.0" encoding="UTF-8"?>  
<beans xmlns="http://www.springframework.org/schema/beans"  
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd">  
      
    <bean class="com.springdemo.postProcessor.MyBeanPostProcessor"></bean>  
    <!--我们先把BeanFactoryPostProcessor注释掉，不启用,然后查看测试输出结果    
    <bean class="com.springdemo.postProcessor.MyBeanFactoryPostProcessor"></bean>  
    -->  
    <bean id="postProcessorBean" class="com.springdemo.postProcessor.PostProcessorBean" >  
        <property name="username" value="test"></property>  
        <property name="password" value="test"></property>  
    </bean>  
</beans>

测试输出结果如下：

PostProcessorBean Bean initializing
username:test
PostProcessorBean Bean initialized
username:test
---------------testBeanFactoryPostProcessor----------------
username:test
password:test

然后我们取消注释启用MyBeanFactoryPostProcessor，测试结果如下：

PostProcessorBean Bean initializing
username:xiaojun
PostProcessorBean Bean initialized
username:xiaojun
---------------testBeanFactoryPostProcessor----------------
username:xiaojun
password:test

从结果可以看出：BeanFactoryPostProcessor的回调比BeanPostProcessor要早，因为BeanPostProcess中输出的username已经变成了xiaojun,而不是test.还有就是BeanFactoryPostProcessor确实有能力改变初始化BEAN的内容.

BeanPostProcessor也能改变bean的值。但值得奇怪的是，如果在BeanFactoryPostProcessor里面调用factory.getBean()，则会对bean进行初始化，但是这个初始化过程不会回调BeanPostProcessor的两个回调方法。