一.再看BeanPostProcessor

BeanPostProcessor是一个接口,用于bean初始化的增强.

1591939521.jpg

我们从图中可以看出,spring工厂通过JDK动态代理,对UserService进行了加工,从而,导致我们在获取getBean获取的时候,其实拿到的是Spring工厂生成的代理对象proxy.

二.编码:

2.1 UserService接口

package com.baizhiedu.factory;

import com.baizhiedu.proxy.User;

public interface UserService {

    void login(String name,int age);

    void register(User user);
}

2.2 UserServiceImpl实现

package com.baizhiedu.factory;


import com.baizhiedu.proxy.User;

/**
 * 原始对象
 */
public class UserServiceImpl implements UserService{


    public void login(String name, int age) {
        System.out.println("UserServiceImpl.login");
    }

    public void register(User user) {
        System.out.println("UserServiceImpl.register");
    }
}

2.3 基于BeanPostProcessor接口+jdk动态代理,生成的具有额外功能的代理对象

package com.baizhiedu.factory;


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

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

/**
 * 增强bean
 */
public class ProxyBeanPostProcessor implements BeanPostProcessor {

    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    public Object postProcessAfterInitialization(final Object bean, String beanName) throws BeansException {
        /**
         * 基于JDK动态代理实现bean的增强
         * 类加载器:借一个
         * interfaces: bean代表了原始类,在原始类中获取
         * invocationHandler: 额外功能+原始类的原始方法运行
         */
        Object o = Proxy.newProxyInstance(ProxyBeanPostProcessor.class.getClassLoader(), bean.getClass().getInterfaces(), new InvocationHandler() {
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                System.out.println("~~~~~额外功能~~~~~");
                Object ret = method.invoke(bean, args);
                return ret;
            }
        });
        //最终返回基于接口,实现的动态代理对象
        return o;
    }
}

2.4 applicationContext.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:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">


    <bean id="userService" class="com.baizhiedu.factory.UserServiceImpl"></bean>

    <bean class="com.baizhiedu.factory.ProxyBeanPostProcessor" id="beanPostProcessor"></bean>

</beans>

2.5 Test测试类:

package com.baizhiedu.factory;

import com.baizhiedu.proxy.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
  public static void main(String[] args) {

      ApplicationContext ctx=new ClassPathXmlApplicationContext("applicationContext6.xml");
      UserService userService = (UserService) ctx.getBean("userService");
      userService.login("Nisy",20);
      userService.register(new User());
  }
}

2.7 测试结果:

.ClassPathXmlApplicationContext@6d9c638
2020-06-12 13:18:31 DEBUG XmlBeanDefinitionReader:395 - Loaded 2 bean definitions from class path resource [applicationContext6.xml]
2020-06-12 13:18:31 DEBUG DefaultListableBeanFactory:213 - Creating shared instance of singleton bean 'beanPostProcessor'
2020-06-12 13:18:31 DEBUG DefaultListableBeanFactory:213 - Creating shared instance of singleton bean 'userService'
~~~~~额外功能~~~~~
UserServiceImpl.login
~~~~~额外功能~~~~~
UserServiceImpl.register