【Spring】对象后期处理，BeanPostProcessor

当我们使用Spring容器管理对象时，需要对对象进行一些后期处理时，比如数据处理、数据预加载，可以使用BeanPostProcessor接口。

简单演示它的用法。

定义扫描包，显示定义BeanPostProcessor的实现类：

<?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:context="http://www.springframework.org/schema/context" 
    xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/context 
           http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <!-- scan the component from the base package -->
    <context:component-scan base-package="com.nicchagil.springapplication.No004BeanPostProcessor" />
    
    <bean id="myBeanPostProcessor" class="com.nicchagil.springapplication.No004BeanPostProcessor.MyBeanPostProcessor" />
    
</beans>

实现BeanPostProcessor：

package com.nicchagil.springapplication.No004BeanPostProcessor;

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

public class MyBeanPostProcessor implements BeanPostProcessor {
    
    public Object postProcessBeforeInitialization(Object obj, String arg1)
            throws BeansException {
        if (obj != null) {
            System.out.println("postProcessBeforeInitialization : " + obj.getClass().getName());
        }
        
        if (obj instanceof UserService) {
            System.out.println("some operation in this point.");
        }
        
        return obj;
    }

    public Object postProcessAfterInitialization(Object obj, String arg1)
            throws BeansException {
        if (obj != null) {
            System.out.println("postProcessAfterInitialization : " + obj.getClass().getName());
        }
        
        if (obj instanceof UserService) {
            System.out.println("some operation in this point.");
        }
        
        return obj;
    }

}

被操作的bean：

package com.nicchagil.springapplication.No004BeanPostProcessor;

import org.springframework.stereotype.Service;

@Service
public class UserService {
    
    public void queryUser() {
        System.out.println("query user method.");
    }

}

用于测试的入口类：

package com.nicchagil.springapplication.No004BeanPostProcessor;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class HowToUse {

    public static void main(String[] args) {
        ApplicationContext context =
                new ClassPathXmlApplicationContext("spring.xml");
        UserService us = context.getBean("userService", UserService.class);
        us.queryUser();
    }

}

日志：

七月 11, 2016 10:31:13 下午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@427a39ea: startup date [Mon Jul 11 22:31:13 CST 2016]; root of context hierarchy
七月 11, 2016 10:31:13 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [spring.xml]
七月 11, 2016 10:31:13 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
信息: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@6371be16: defining beans [userService,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,myBeanPostProcessor,org.springframework.context.annotation.ConfigurationClassPostProcessor.importAwareProcessor]; root of factory hierarchy
postProcessBeforeInitialization : com.nicchagil.springapplication.No004BeanPostProcessor.UserService
some operation in this point.
postProcessAfterInitialization : com.nicchagil.springapplication.No004BeanPostProcessor.UserService
some operation in this point.
query user method.