Spring基础学习（七）——对bean初始化的加工（BeanPostProcessor）

向右看齐 2022-05-31 02:22 116阅读 0赞

spring提供了很多扩展接口，其中就包括有BeanPostProcessor,其作用是——当我们在Spring容器中完成bean的实例化、配置以及其他初始化方法前后要添加一些自己的事务处理逻辑时，我们需要定义一个或者多个BeanPosrtProcessor接口实现类，然后注册到Spring容器中。

首先，BeanPostProcessor的说明如下：

public interface BeanPostProcessor {  
      
        /** 
         * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean 
         * initialization callbacks (like InitializingBean's {@code afterPropertiesSet} 
         * or a custom init-method). The bean will already be populated with property values.    
         */  
        //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;  
      
          
        /** 
         * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean 
         * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}   
         * or a custom init-method). The bean will already be populated with property values.       
         */  
        //实例化、依赖注入、初始化完毕时执行  
        Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;  
      
    }

可以看出，对bean初始化的加工逻辑很简单，只需要定义一个 BeanPostProcessor的实现类，如果我们需要在bean的实例化前添加事务逻辑，则需要在postProcessBeforeInitialization（）方法中写逻辑操作，如果我们需要在bean的实例化完成后添加事务逻辑，则需要在postProcessAfterInitialization（）方法中写逻辑操作。

具体例子如下：

UserService层代码：

public class UserServiceImpl implements UserService {
    
    	@Override
    	public void addUser() {
    		// TODO Auto-generated method stub
    		System.out.println("添加用户");
    		
    	}
    
    	@Override
    	public User queryUserByXX() {
    		// TODO Auto-generated method stub
    		System.out.println("查找用户");
    		return null;
    	}
    
    	@Override
    	public void update() {
    		System.out.println("更新用户");
    		// TODO Auto-generated method stub
    		
    	}
    
    	@Override
    	public void delete() {
    		System.out.println("删除用户");
    		// TODO Auto-generated method stub
    		
    	}
    
    }

MyBeanPostProcessor实现BeanPostProcessor接口，实现对bean实例化的加工

public class MyBeanPostProcessor implements BeanPostProcessor{
    
    	@Override
    	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    		// TODO Auto-generated method stub
    		System.out.println("bean初始化前"+beanName);
    		return bean;
    	}
    
    	@Override
    	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    		// TODO Auto-generated method stub
    		System.out.println("bean初始化后"+beanName);
    		return bean;
    	}
    
    }

注意： MyBeanPostProcessor中的两个方法返回值都不能是null,如果返回null,那么在后续初始化方法中将会报空指针异常或者通过getBean()方法获取不到实例化对象，因为实例化的对象没有放回到SpringIOC容器中。

XML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"
    	xmlns:aop="http://www.springframework.org/schema/aop"
    	xmlns:context="http://www.springframework.org/schema/context"
    	xmlns:tx="http://www.springframework.org/schema/tx"
    	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
    		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd
    		http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.3.xsd
    		http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.3.xsd">
    
    
    <bean id="MyBeanPostProcessor" class="net.seehope.springAOP.MyBeanPostProcessor"></bean>
    <bean id="userServiceImpl" class="net.seehope.springAOP.UserServiceImpl"></bean>
    
    </beans>

测试代码：

public class PostTest {
    	
    	@Test
    	public void test(){
    		ApplicationContext context = new ClassPathXmlApplicationContext("spring/applicationContext.xml");
    		UserServiceImpl userService = (UserServiceImpl) context.getBean("userServiceImpl");
    		userService.queryUserByXX();
    	}

测试结果： ![SouthEast][]

结果显示说明我们在调用bean之前，bean已经实现了初始化前和初始后的逻辑。

那么，如何实现调用多个BeanPostProcessor，具体例子如下：

首先，实现类应该同时实现BeanPostProcessor和Ordered,实现Ordered接口的getOrder方法，该方法返回一整数，返回值越小，优先级越高，默认为0；

如果不实现Ordered接口，则按照applicationContext.xml（spring配置文件）中声明的先后顺序执行

实现类MyBeanPostProcessor代码：

import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    import org.springframework.core.Ordered;
    
    public class MyBeanPostProcessor implements BeanPostProcessor,Ordered{
    
    	@Override
    	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    		// TODO Auto-generated method stub
    		System.out.println("bean初始化前"+beanName+"0");
    		return bean;
    	}
    
    	@Override
    	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    		// TODO Auto-generated method stub
    		System.out.println("bean初始化后"+beanName+"0");
    		return bean;
    	}
    
    	@Override
    	public int getOrder() {
    		// TODO Auto-generated method stub
    		return 0;
    	}
    
    }

实现类MyBeanPostProcessor2代码：

import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    import org.springframework.core.Ordered;
    
    public class MyBeanPostProcessor2 implements BeanPostProcessor,Ordered{
    
    	@Override
    	public int getOrder() {
    		// TODO Auto-generated method stub
    		return 1;
    	}
    
    	@Override
    	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    		System.out.println("初始化方法前"+beanName+"1");
    		return bean;
    	}
    
    	@Override
    	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    		// TODO Auto-generated method stub
    		System.out.println("初始化方法后"+beanName+"1");
    		return bean;
    	}
    
    }

XML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"
    	xmlns:aop="http://www.springframework.org/schema/aop"
    	xmlns:context="http://www.springframework.org/schema/context"
    	xmlns:tx="http://www.springframework.org/schema/tx"
    	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
    		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd
    		http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.3.xsd
    		http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.3.xsd">
    
    
    
    <bean id="MyBeanPostProcessor" class="net.seehope.springAOP.MyBeanPostProcessor"></bean>
    <bean id="MyBeanPostProcessor2" class="net.seehope.springAOP.MyBeanPostProcessor2"></bean>
    <bean id="userServiceImpl" class="net.seehope.springAOP.UserServiceImpl"></bean>
    
    </beans>

其余代码相同，不再显示，测试结果如下：

![SouthEast 1][]

有结果可见，bean的实例化加工顺序按设定的优先级执行

[SouthEast]: /images/20220531/16007aa041b74ca69601b004bf2363f5.png
[SouthEast 1]: /images/20220531/5dca801bcc9448549001752a04f0c0e2.png