Spring中的后置处理器BeanPostProcessor讲解

Posted 2022-06-14 deityjian

BeanPostProcessor接口作用：

     如果我们想在Spring容器中完成bean实例化、配置以及其他初始化方法前后要添加一些自己逻辑处理。我们需要定义一个或多个BeanPostProcessor接口实现类，然后注册到Spring IoC容器中。

package com.test.spring;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
/**
 * bean后置处理器
 * @author zss
 *
 */
public class PostProcessor implements BeanPostProcessor 

    @Override
    public Object postProcessBeforeInitialization(Object bean,
            String beanName) throws BeansException 
        if ("narCodeService".equals(beanName)) //过滤掉bean实例ID为narCodeService
            return bean;
        
        System.out.println("后置处理器处理bean=【"+beanName+"】开始");
        try 
            Thread.sleep(1000);
         catch (InterruptedException e) 
            e.printStackTrace();
        
        return bean;
    

    @Override
    public Object postProcessAfterInitialization(Object bean,
            String beanName) throws BeansException 
        if ("narCodeService".equals(beanName)) 
            return bean;
        
        System.out.println("后置处理器处理bean=【"+beanName+"】完毕!");
        try 
            Thread.sleep(1000);
         catch (InterruptedException e) 
            e.printStackTrace();
        
        return bean;
    

注意:接口中两个方法不能返回null，如果返回null那么在后续初始化方法将报空指针异常或者通过getBean()方法获取不到bena实例对象，因为后置处理器从Spring IoC容器中取出bean实例对象没有再次放回IoC容器中！

将Spring的后置处理器PostProcessor配置到Spring配置文件中

<?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.xsd">

    <!-- 定义一个bean -->
     <bean id="narCodeService" class="com.test.service.impl.NarCodeServiceImpl">
     </bean>
    <bean id="beanLifecycle" class="com.test.spring.BeanLifecycle" init-method="init" destroy-method="close">
        <property name="name" value="张三"></property>
        <property name="sex" value="男"></property>
    </bean>

    <!-- Spring后置处理器 -->
    <bean id="postProcessor" class="com.test.spring.PostProcessor"/>
</beans>

BeanPostProcessor API：

public interface BeanPostProcessor   
  
    //实例化、依赖注入完毕，在调用显示的初始化之前完成一些定制的初始化任务  
    Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;  
  
     
    //实例化、依赖注入、初始化完毕时执行  
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;  
  

由API可以看出:
1：后置处理器的postProcessorBeforeInitailization方法是在bean实例化，依赖注入之后及自定义初始化方法(例如：配置文件中bean标签添加init-method属性指定Java类中初始化方法、
@PostConstruct注解指定初始化方法，Java类实现InitailztingBean接口)之前调用
2：后置处理器的postProcessorAfterInitailization方法是在bean实例化、依赖注入及自定义初始化方法之后调用

注意：
   1.BeanFactory和ApplicationContext两个容器对待bean的后置处理器稍微有些不同。ApplicationContext容器会自动检测Spring配置文件中那些bean所对应的Java类实现了BeanPostProcessor
接口，并自动把它们注册为后置处理器。在创建bean过程中调用它们，所以部署一个后置处理器跟普通的bean没有什么太大区别。

      2.BeanFactory容器注册bean后置处理器时必须通过代码显示的注册，在IoC容器继承体系中的ConfigurableBeanFactory接口中定义了注册方法

   void addBeanPostProcessor(BeanPostProcessor beanPostProcessor);

 Spring如何调用多个BeanPostProcessor实现类：

    我们可以在Spring配置文件中添加多个BeanPostProcessor(后置处理器)接口实现类，在默认情况下Spring容器会根据后置处理器的定义顺序来依次调用。

Spring配置文件：

<?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.xsd">
    <!-- bean定义 -->    
    <bean id="narCodeService" class="com.test.service.impl.NarCodeServiceImpl">
    </bean>
    <bean id="postProcessor" class="com.test.spring.PostProcessor"/>
    <bean id="postProcessorB" class="com.test.spring.PostProcessorB"/>
</beans>

BeanPostProcessor实现类：

package com.test.spring;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
/**
 * bean后置处理器
 * @author zss
 *
 */
public class PostProcessor implements BeanPostProcessor 

    @Override
    public Object postProcessBeforeInitialization(Object bean,
            String beanName) throws BeansException 
        System.out.println("后置处理器处理bean=【"+beanName+"】开始");
        try 
            Thread.sleep(1000);
         catch (InterruptedException e) 
            e.printStackTrace();
        
        return bean;
    

    @Override
    public Object postProcessAfterInitialization(Object bean,
            String beanName) throws BeansException 
        System.out.println("后置处理器处理bean=【"+beanName+"】完毕!");
        try 
            Thread.sleep(1000);
         catch (InterruptedException e) 
            e.printStackTrace();
        
        return bean;
    

----------------------------------------------------------------------------------------------------------------------------------------
package com.test.spring;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

public class PostProcessorB implements BeanPostProcessor 

    @Override
    public Object postProcessBeforeInitialization(Object bean,
            String beanName) throws BeansException 
        System.out.println("后置处理器开始调用了");
        try 
            Thread.sleep(1000);
         catch (InterruptedException e) 
            e.printStackTrace();
        
        return bean;
    

    @Override
    public Object postProcessAfterInitialization(Object bean,
            String beanName) throws BeansException 
        System.out.println("后置处理器调用结束了");
        try 
            Thread.sleep(1000);
         catch (InterruptedException e) 
            e.printStackTrace();
        
        return bean;
    

Test case:

package com.test.spring;

import org.junit.Before;
import org.junit.Test;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class T 
    AbstractApplicationContext applicationcontext=null;
    @Before
    public void before() 
        System.out.println("》》》Spring ApplicationContext容器开始初始化了......");
        applicationcontext= new ClassPathXmlApplicationContext(new String[]"test1-service.xml");
        System.out.println("》》》Spring ApplicationContext容器初始化完毕了......");
    
    @Test
    public void  test() 
        applicationcontext.registerShutdownHook();   
    

测试结果：

》》》Spring ApplicationContext容器开始初始化了......
2017-03-19 10:50:29  INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@18c92ff9: startup date [Sun Mar 19 10:50:29 CST 2017]; root of context hierarchy
2017-03-19 10:50:29  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
后置处理器处理bean=【narCodeService】开始
后置处理器开始调用了
后置处理器处理bean=【narCodeService】完毕!
后置处理器调用结束了
》》》Spring ApplicationContext容器初始化完毕了......
2017-03-19 10:50:34  INFO:ClassPathXmlApplicationContext-Closing org.springframework.context.support.ClassPathXmlApplicationContext@18c92ff9: startup date [Sun Mar 19 10:50:29 CST 2017]; root of context hierarchy

在Spring机制中可以指定后置处理器调用顺序，通过让BeanPostProcessor接口实现类实现Ordered接口getOrder方法，该方法返回一整数，默认值为 0，优先级最高，值越大优先级越低