Spring高级-容器实现-BeanFactory后处理器排序（一）

一、开胃菜：入门级面试题：如果一个接口有多个实现类，想取到其中某一个Bean怎么进行一个依赖注入

1、代码

package com.mangoubiubiu.show;

import lombok.extern.slf4j.Slf4j;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigUtils;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.logging.Logger;

public class TestBeanFactory {

    public static void main(String[] args) {

        DefaultListableBeanFactory beanFactory=new DefaultListableBeanFactory();

        //bean 的定义 （class  ,scope , 初始化 ，销毁方法）

        AbstractBeanDefinition beanDefinition
                = BeanDefinitionBuilder.genericBeanDefinition(Config.class).setScope("singleton").getBeanDefinition();
        beanFactory.registerBeanDefinition("config",beanDefinition);

        //给 BeanFactory 添加一些常用的后处理器
        AnnotationConfigUtils.registerAnnotationConfigProcessors(beanFactory);


        //BeanFactory 后处理器主要功能，补充了一些bean的定义
       beanFactory.getBeansOfType(BeanFactoryPostProcessor.class).values().stream().forEach(beanFactoryPostProcessor -> {
           beanFactoryPostProcessor.postProcessBeanFactory(beanFactory);
       });

       //Bean后处理器，针对 bean 的生命周期的各个阶段提供扩展，例如@Autowired @Resource
      //  beanFactory.getBeansOfType(BeanPostProcessor.class).values().forEach(beanFactory::addBeanPostProcessor);
        beanFactory.getBeansOfType(BeanPostProcessor.class).values().forEach(beanPostProcessor -> {
            beanFactory.addBeanPostProcessor(beanPostProcessor);//建立bean工厂与后处理器之间的联系
        });

        for(String name  : beanFactory.getBeanDefinitionNames()){
            System.out.println(name);
        }
        beanFactory.preInstantiateSingletons();//准备好所有的单列对象
        System.out.println("----------------->");

        Bean1 bean = beanFactory.getBean(Bean1.class);
        System.out.println("成功取到Bean2的对象:"+bean.getBean2());

        System.out.println("----------------->");

        System.out.println("成功取到Bean2的对象:"+bean.getInner());
  
    }



    @Configuration
    static class Config{
        @Bean
        public Bean1 bean1(){
            return new Bean1();
        }
        @Bean
        public Bean2 bean2(){
            return new Bean2();
        }
        @Bean
        public Bean3 bean3(){
            return new Bean3();
        }
        @Bean
        public Bean4 bean4(){
            return new Bean4();
        }
    }

    interface Inner{ }

    static class Bean3 implements Inner{}
    static class Bean4 implements Inner{}


    @Slf4j
    static class Bean1 {
        public Bean1(){
            log.info("构造 Bean1");
        }

        @Autowired
        private Bean2 bean2;

        public Bean2 getBean2(){
            return bean2;
        }
        @Autowired
        @Qualifier("bean4")
        private Inner inner;

        public Inner getInner(){
            return inner;
        }

    }


    @Slf4j
    static class Bean2{
        public Bean2(){
            log.info("构造 Bean2");
        }

    }


}