Spring底层原理学习笔记--第六讲--(Aware与InitializingBean接口及@Autowired失效分析)

1.Aware接口提供了一种【内置】的注入手段，可以注入BeanFactory，ApplicationContext
2.InitiazingBean接口提供了一种【内置】的初始化手段
3.内置的注入和初始化不收扩展功能的影响，总会被执行，因此Spring框架内部的类常用它们
4.实战：@Autowired失效分析

Aware与InitializingBean接口

A06Application.java

package com.lucifer.itheima.a06;

import org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor;
import org.springframework.context.annotation.CommonAnnotationBeanPostProcessor;
import org.springframework.context.support.GenericApplicationContext;

/**
 * Aware接口及InitializingBean接口
 */
public class A06Application {

    public static void main(String[] args) {
        /*
        1.Aware接口用于注入一些与容器相关信息，例如
            a.BeanNameAware 注入bean的名字
            b.BeanFactoryAware 注入BeanFactory容器
            c.ApplicationContextAware注入ApplicationContext容器
            d.EmbeddedValueResolverAware ${}
         */

        // 输出结果为
//        15:56:19.704 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@5bcab519 名字叫：myBean
//        15:56:19.706 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@5bcab519 容器是：org.springframework.context.support.GenericApplicationContext@5aaa6d82, started on Wed Nov 08 15:56:19 CST 2023
//        15:56:19.706 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@5bcab519初始化
        GenericApplicationContext context = new GenericApplicationContext();
        context.registerBean("myBean",MyBean.class);

        //不加这两句
//        context.registerBean(AutowiredAnnotationBeanPostProcessor.class);
//        context.registerBean(CommonAnnotationBeanPostProcessor.class);
        //的输出结果是
//        16:26:47.976 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@5bcab519 名字叫：myBean
//        16:26:47.979 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@5bcab519 容器是：org.springframework.context.support.GenericApplicationContext@5aaa6d82, started on Wed Nov 08 16:26:47 CST 2023
//        16:26:47.979 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@5bcab519初始化

        // 加上那两句（后处理器）的输出结果是
//        16:28:24.501 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@262b2c86 使用！Autowired 容器是:org.springframework.context.support.GenericApplicationContext@5aaa6d82, started on Wed Nov 08 16:28:24 CST 2023
//        16:28:24.501 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@262b2c86 名字叫：myBean
//        16:28:24.501 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@262b2c86 容器是：org.springframework.context.support.GenericApplicationContext@5aaa6d82, started on Wed Nov 08 16:28:24 CST 2023
//        16:28:24.501 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@262b2c86 使用@PostConstruct 初始化
//        16:28:24.501 [main] INFO com.lucifer.itheima.a06.MyBean - 当前bean com.lucifer.itheima.a06.MyBean@262b2c86初始化
        context.registerBean(AutowiredAnnotationBeanPostProcessor.class);
        context.registerBean(CommonAnnotationBeanPostProcessor.class);
        context.refresh();
        context.close();
        /**
         * 2.b、c、d的功能用！Autowired就能实现，为什么还要用Aware接口
         * 简单地说：
         *      a.@Autowired的解析需要用到bean后处理器，属于扩展功能
         *      b.而Aware接口属于内置功能，不加任何扩展，Spring就能识别
         * 某些情况下，扩展功能会实现，而内置功能不会生效
         *
         * 问1：你会发现用Aware注入ApplicationContext成功，而@Autowired注入ApplicaitonContext失效
         */
    }
}

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MyBean.java

package com.lucifer.itheima.a06;

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

import javax.annotation.PostConstruct;

@Slf4j
public class MyBean implements BeanNameAware, ApplicationContextAware, InitializingBean {

    @Override
    public void setBeanName(String name) {
        log.info("当前bean "+ this + " 名字叫：" + name);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        log.info("当前bean " + this + " 容器是：" + applicationContext);
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        log.info("当前bean " + this + "初始化");
    }

    @Autowired
    public void aaa(ApplicationContext applicationContext) {
        log.info("当前bean " + this + " 使用！Autowired 容器是:" + applicationContext);
    }

    @PostConstruct
    public void init() {
        log.info("当前bean " + this + " 使用@PostConstruct 初始化");
    }
}

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@Autowired失效分析

A06Application.java

package com.lucifer.itheima.a06;

import org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor;
import org.springframework.context.annotation.CommonAnnotationBeanPostProcessor;
import org.springframework.context.annotation.ConfigurationClassPostProcessor;
import org.springframework.context.support.GenericApplicationContext;

/**
 * Aware接口及InitializingBean接口
 */
public class A06Application {

    public static void main(String[] args) {
        /*
        1.Aware接口用于注入一些与容器相关信息，例如
            a.BeanNameAware 注入bean的名字
            b.BeanFactoryAware 注入BeanFactory容器
            c.ApplicationContextAware注入ApplicationContext容器
            d.EmbeddedValueResolverAware ${}
         */

        GenericApplicationContext context = new GenericApplicationContext();
//        context.registerBean("myBean",MyBean.class);
//        context.registerBean("myConfig1",MyConfig1.class);
        context.registerBean("myConfig2",MyConfig2.class);


        context.registerBean(AutowiredAnnotationBeanPostProcessor.class);  //能解析@Autowired注解
        context.registerBean(CommonAnnotationBeanPostProcessor.class);     //能解析@PostConstruct注解
        context.registerBean(ConfigurationClassPostProcessor.class);  //能解析@ComponentScan @Bean @Import @ImportResource

        context.refresh();   //1.会到容器中找到所有beanFactory后处理器来执行 2.添加bean后处理器  3.初始化单例
        context.close();
        /**
         * 2.b、c、d的功能用！Autowired就能实现，为什么还要用Aware接口
         * 简单地说：
         *      a.@Autowired的解析需要用到bean后处理器，属于扩展功能
         *      b.而Aware接口属于内置功能，不加任何扩展，Spring就能识别
         * 某些情况下，扩展功能会实现，而内置功能不会生效
         *
         * 问1：你会发现用Aware注入ApplicationContext成功，而@Autowired注入ApplicaitonContext失效
         */

        /**
         *学到了什么
         *     a.Aware接口提供了一种[内置]的注入手段，可以注入BeanFactory，ApplicationContext
         *     b.InitializingBean接口提供了一种【内置】的初始化手段
         *     c.内置的注入和初始化不受扩展功能的影响，总会被执行，因此Spring框架内的类常用它们
         */
    }
}

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MyConfig1.java

package com.lucifer.itheima.a06;

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

@Configuration
@Slf4j
public class MyConfig1 {

    @Autowired
    public void setApplicationContext(ApplicationContext applicationContext) {
        log.info("注入 ApplicationContext");
    }

    @PostConstruct
    public void init() {
        log.info("初始化");
    }

    @Bean // beanFactory后处理器
    public BeanFactoryPostProcessor processor1() {
        return beanFactory -> {
            log.info("执行 processor1");
        };
    }

}

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MyConfig2.java

package com.lucifer.itheima.a06;

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@Slf4j
public class MyConfig2 implements InitializingBean, ApplicationContextAware {
    @Override
    public void afterPropertiesSet() throws Exception {
        log.info("初始化");
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        log.info("注入 ApplicationContext");
    }

    @Bean // beanFactory后处理器
    public BeanFactoryPostProcessor processor1() {
        return beanFactory -> {
            log.info("执行 processor1");
        };
    }
}

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原文地址：https://blog.csdn.net/weixin_42594143/article/details/134293139