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spring高级源码50讲-1-8(spring容器与bean)

news 文章来源：https://blog.csdn.net/kuangzeng/article/details/132627890 2025/2/10 7:59:14

文章目录

- 容器与 bean
- - 1) 容器接口
  - - 演示1 - BeanFactory 与 ApplicationContext 的区别
    - - 关键代码参考
    - 收获💡
    - 演示2 - 国际化
  - 2) 容器实现
  - - 演示1 - DefaultListableBeanFactory
    - - 代码参考
    - 收获💡
    - 演示2 - 常见 ApplicationContext 实现
    - - 代码参考
    - 收获💡
  - 3) Bean 的生命周期
  - - 演示1 - bean 生命周期
    - - 代码参考
    - 收获💡
    - 演示2 - 模板方法设计模式
    - - 关键代码
    - 演示3 - bean 后处理器排序
    - - 代码参考
    - 收获💡
  - 4) Bean 后处理器
  - - 演示1 - 后处理器作用
    - - 代码参考
    - 收获💡
    - 演示2 - @Autowired bean 后处理器运行分析
    - - 代码参考
    - 收获💡
  - 5) BeanFactory 后处理器
  - - 演示1 - BeanFactory 后处理器的作用
    - - 代码参考
    - 收获💡
    - 演示2 - 模拟解析 @ComponentScan
    - - 代码参考
    - 收获💡
    - 演示3 - 模拟解析 @Bean
    - - 代码参考
    - 收获💡
    - 演示4 - 模拟解析 Mapper 接口
    - - 代码参考
    - 收获💡
  - 6) Aware 接口
  - - 演示 - Aware 接口及 InitializingBean 接口
    - - 代码参考
    - 收获💡
    - 配置类 @Autowired 失效分析
  - 7) 初始化与销毁
  - - 演示 - 初始化销毁顺序
    - - 代码参考
    - 收获💡
  - 8) Scope
  - - 演示1 - request, session, application 作用域
    - - 代码参考
    - 收获💡
    - 分析 - singleton 注入其它 scope 失效
    - 演示2 - 4种解决方法
    - - 代码参考
    - 收获💡

容器与 bean

1) 容器接口

BeanFactory 接口，典型功能有：
- getBean
ApplicationContext 接口，是 BeanFactory 的子接口。它扩展了 BeanFactory 接口的功能，如：
- 国际化
- 通配符方式获取一组 Resource 资源
- 整合 Environment 环境（能通过它获取各种来源的配置信息）
- 事件发布与监听，实现组件之间的解耦

可以看到，我们课上讲的，都是 BeanFactory 提供的基本功能，ApplicationContext 中的扩展功能都没有用到。

演示1 - BeanFactory 与 ApplicationContext 的区别

关键代码参考

package com.itheima.a01;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.DefaultSingletonBeanRegistry;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.io.Resource;import java.io.IOException;
import java.lang.reflect.Field;
import java.util.Locale;
import java.util.Map;/*BeanFactory 与 ApplicationContext 的区别*/
@SpringBootApplication
public class A01 {private static final Logger log = LoggerFactory.getLogger(A01.class);public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException, IOException {ConfigurableApplicationContext context = SpringApplication.run(A01.class, args);/*1. 到底什么是 BeanFactory- 它是 ApplicationContext 的父接口- 它才是 Spring 的核心容器, 主要的 ApplicationContext 实现都【组合】了它的功能*/System.out.println(context);/*2. BeanFactory 能干点啥- 表面上只有 getBean- 实际上控制反转、基本的依赖注入、直至 Bean 的生命周期的各种功能, 都由它的实现类提供*/Field singletonObjects = DefaultSingletonBeanRegistry.class.getDeclaredField("singletonObjects");singletonObjects.setAccessible(true);ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();Map<String, Object> map = (Map<String, Object>) singletonObjects.get(beanFactory);map.entrySet().stream().filter(e -> e.getKey().startsWith("component")).forEach(e -> {System.out.println(e.getKey() + "=" + e.getValue());});/*3. ApplicationContext 比 BeanFactory 多点啥*/System.out.println(context.getMessage("hi", null, Locale.CHINA));System.out.println(context.getMessage("hi", null, Locale.ENGLISH));System.out.println(context.getMessage("hi", null, Locale.JAPANESE));Resource[] resources = context.getResources("classpath*:META-INF/spring.factories");for (Resource resource : resources) {System.out.println(resource);}System.out.println(context.getEnvironment().getProperty("java_home"));System.out.println(context.getEnvironment().getProperty("server.port"));//        context.publishEvent(new UserRegisteredEvent(context));context.getBean(Component1.class).register();/*4. 学到了什么a. BeanFactory 与 ApplicationContext 并不仅仅是简单接口继承的关系, ApplicationContext 组合并扩展了 BeanFactory 的功能b. 又新学一种代码之间解耦途径练习：完成用户注册与发送短信之间的解耦, 用事件方式、和 AOP 方式分别实现*/}
}

package com.itheima.a01;import org.springframework.context.ApplicationEvent;public class UserRegisteredEvent extends ApplicationEvent {public UserRegisteredEvent(Object source) {super(source);}
}

package com.itheima.a01;import org.aspectj.lang.annotation.Aspect;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.stereotype.Component;@Component
public class Component1 {private static final Logger log = LoggerFactory.getLogger(Component1.class);@Autowiredprivate ApplicationEventPublisher context;public void register() {log.debug("用户注册");context.publishEvent(new UserRegisteredEvent(this));}}

package com.itheima.a01;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.event.EventListener;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;@Component
public class Component2 {private static final Logger log = LoggerFactory.getLogger(Component2.class);@EventListenerpublic void aaa(UserRegisteredEvent event) {log.debug("{}", event);log.debug("发送短信");}
}

收获💡

通过这个示例结合 debug 查看 ApplicationContext 对象的内部结构，学到：

到底什么是 BeanFactory
- 它是 ApplicationContext 的父接口
- 它才是 Spring 的核心容器, 主要的 ApplicationContext 实现都【组合】了它的功能，【组合】是指 ApplicationContext 的一个重要成员变量就是 BeanFactory
BeanFactory 能干点啥
- 表面上只有 getBean
- 实际上控制反转、基本的依赖注入、直至 Bean 的生命周期的各种功能，都由它的实现类提供
- 例子中通过反射查看了它的成员变量 singletonObjects，内部包含了所有的单例 bean
ApplicationContext 比 BeanFactory 多点啥
- ApplicationContext 组合并扩展了 BeanFactory 的功能
- 国际化、通配符方式获取一组 Resource 资源、整合 Environment 环境、事件发布与监听
- 新学一种代码之间解耦途径，事件解耦

建议练习：完成用户注册与发送短信之间的解耦，用事件方式、和 AOP 方式分别实现

注意

如果 jdk > 8, 运行时请添加 --add-opens java.base/java.lang=ALL-UNNAMED，这是因为这些版本的 jdk 默认不允许跨 module 反射
事件发布还可以异步，这个视频中没有展示，请自行查阅 @EnableAsync，@Async 的用法

演示2 - 国际化

public class TestMessageSource {public static void main(String[] args) {GenericApplicationContext context = new GenericApplicationContext();context.registerBean("messageSource", MessageSource.class, () -> {ResourceBundleMessageSource ms = new ResourceBundleMessageSource();ms.setDefaultEncoding("utf-8");ms.setBasename("messages");return ms;});context.refresh();System.out.println(context.getMessage("hi", null, Locale.ENGLISH));System.out.println(context.getMessage("hi", null, Locale.CHINESE));System.out.println(context.getMessage("hi", null, Locale.JAPANESE));}
}

国际化文件均在 src/resources 目录下

messages.properties（空）

messages_en.properties

hi=Hello

messages_ja.properties

hi=こんにちは

messages_zh.properties

hi=你好

注意

ApplicationContext 中 MessageSource bean 的名字固定为 messageSource
使用 SpringBoot 时，国际化文件名固定为 messages
空的 messages.properties 也必须存在

2) 容器实现

Spring 的发展历史较为悠久，因此很多资料还在讲解它较旧的实现，这里出于怀旧的原因，把它们都列出来，供大家参考

DefaultListableBeanFactory，是 BeanFactory 最重要的实现，像控制反转和依赖注入功能，都是它来实现
ClassPathXmlApplicationContext，从类路径查找 XML 配置文件，创建容器（旧）
FileSystemXmlApplicationContext，从磁盘路径查找 XML 配置文件，创建容器（旧）
XmlWebApplicationContext，传统 SSM 整合时，基于 XML 配置文件的容器（旧）
AnnotationConfigWebApplicationContext，传统 SSM 整合时，基于 java 配置类的容器（旧）
AnnotationConfigApplicationContext，Spring boot 中非 web 环境容器（新）
AnnotationConfigServletWebServerApplicationContext，Spring boot 中 servlet web 环境容器（新）
AnnotationConfigReactiveWebServerApplicationContext，Spring boot 中 reactive web 环境容器（新）

另外要注意的是，后面这些带有 ApplicationContext 的类都是 ApplicationContext 接口的实现，但它们是组合了 DefaultListableBeanFactory 的功能，并非继承而来

演示1 - DefaultListableBeanFactory

代码参考

package com.itheima.a02;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
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 org.springframework.core.Ordered;import javax.annotation.Resource;public class TestBeanFactory {public static void main(String[] args) {DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();// bean 的定义（class, scope, 初始化, 销毁）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 定义beanFactory.getBeansOfType(BeanFactoryPostProcessor.class).values().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().stream().sorted(beanFactory.getDependencyComparator()).forEach(beanPostProcessor -> {System.out.println(">>>>" + beanPostProcessor);beanFactory.addBeanPostProcessor(beanPostProcessor);});for (String name : beanFactory.getBeanDefinitionNames()) {System.out.println(name);}beanFactory.preInstantiateSingletons(); // 准备好所有单例System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> ");
//        System.out.println(beanFactory.getBean(Bean1.class).getBean2());System.out.println(beanFactory.getBean(Bean1.class).getInter());/*学到了什么:a. beanFactory 不会做的事1. 不会主动调用 BeanFactory 后处理器2. 不会主动添加 Bean 后处理器3. 不会主动初始化单例4. 不会解析beanFactory 还不会解析 ${ } 与 #{ }b. bean 后处理器会有排序的逻辑*/System.out.println("Common:" + (Ordered.LOWEST_PRECEDENCE - 3));System.out.println("Autowired:" + (Ordered.LOWEST_PRECEDENCE - 2));}@Configurationstatic class Config {@Beanpublic Bean1 bean1() {return new Bean1();}@Beanpublic Bean2 bean2() {return new Bean2();}@Beanpublic Bean3 bean3() {return new Bean3();}@Beanpublic Bean4 bean4() {return new Bean4();}}interface Inter {}static class Bean3 implements Inter {}static class Bean4 implements Inter {}static class Bean1 {private static final Logger log = LoggerFactory.getLogger(Bean1.class);public Bean1() {log.debug("构造 Bean1()");}@Autowiredprivate Bean2 bean2;public Bean2 getBean2() {return bean2;}@Autowired@Resource(name = "bean4")private Inter bean3;public Inter getInter() {return bean3;}}static class Bean2 {private static final Logger log = LoggerFactory.getLogger(Bean2.class);public Bean2() {log.debug("构造 Bean2()");}}
}

收获💡

beanFactory 可以通过 registerBeanDefinition 注册一个 bean definition 对象
- 我们平时使用的配置类、xml、组件扫描等方式都是生成 bean definition 对象注册到 beanFactory 当中
- bean definition 描述了这个 bean 的创建蓝图：scope 是什么、用构造还是工厂创建、初始化销毁方法是什么，等等
beanFactory 需要手动调用 beanFactory 后处理器对它做增强
- 例如通过解析 @Bean、@ComponentScan 等注解，来补充一些 bean definition
beanFactory 需要手动添加 bean 后处理器，以便对后续 bean 的创建过程提供增强
- 例如 @Autowired，@Resource 等注解的解析都是 bean 后处理器完成的
- bean 后处理的添加顺序会对解析结果有影响，见视频中同时加 @Autowired，@Resource 的例子
beanFactory 需要手动调用方法来初始化单例
beanFactory 需要额外设置才能解析 ${} 与 #{}

演示2 - 常见 ApplicationContext 实现

代码参考

package com.itheima.a02;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.autoconfigure.web.servlet.DispatcherServletRegistrationBean;
import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
import org.springframework.boot.web.servlet.server.ServletWebServerFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.context.support.FileSystemXmlApplicationContext;
import org.springframework.web.servlet.DispatcherServlet;
import org.springframework.web.servlet.mvc.Controller;/*常见 ApplicationContext 实现*/
public class A02 {private static final Logger log = LoggerFactory.getLogger(A02.class);public static void main(String[] args) {testClassPathXmlApplicationContext();
//        testFileSystemXmlApplicationContext();
//        testAnnotationConfigApplicationContext();
//        testAnnotationConfigServletWebServerApplicationContext();/*DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();System.out.println("读取之前...");for (String name : beanFactory.getBeanDefinitionNames()) {System.out.println(name);}System.out.println("读取之后...");XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(beanFactory);reader.loadBeanDefinitions(new FileSystemResource("src\\main\\resources\\a02.xml"));for (String name : beanFactory.getBeanDefinitionNames()) {System.out.println(name);}*//*学到了什么a. 常见的 ApplicationContext 容器实现b. 内嵌容器、DispatcherServlet 的创建方法、作用*/}// ⬇️较为经典的容器, 基于 classpath 下 xml 格式的配置文件来创建private static void testClassPathXmlApplicationContext() {ClassPathXmlApplicationContext context =new ClassPathXmlApplicationContext("a02.xml");for (String name : context.getBeanDefinitionNames()) {System.out.println(name);}System.out.println(context.getBean(Bean2.class).getBean1());}// ⬇️基于磁盘路径下 xml 格式的配置文件来创建private static void testFileSystemXmlApplicationContext() {FileSystemXmlApplicationContext context =new FileSystemXmlApplicationContext("src\\main\\resources\\a02.xml");for (String name : context.getBeanDefinitionNames()) {System.out.println(name);}System.out.println(context.getBean(Bean2.class).getBean1());}// ⬇️较为经典的容器, 基于 java 配置类来创建private static void testAnnotationConfigApplicationContext() {AnnotationConfigApplicationContext context =new AnnotationConfigApplicationContext(Config.class);for (String name : context.getBeanDefinitionNames()) {System.out.println(name);}System.out.println(context.getBean(Bean2.class).getBean1());}// ⬇️较为经典的容器, 基于 java 配置类来创建, 用于 web 环境private static void testAnnotationConfigServletWebServerApplicationContext() {AnnotationConfigServletWebServerApplicationContext context =new AnnotationConfigServletWebServerApplicationContext(WebConfig.class);for (String name : context.getBeanDefinitionNames()) {System.out.println(name);}}@Configurationstatic class WebConfig {@Beanpublic ServletWebServerFactory servletWebServerFactory(){return new TomcatServletWebServerFactory();}@Beanpublic DispatcherServlet dispatcherServlet() {return new DispatcherServlet();}@Beanpublic DispatcherServletRegistrationBean registrationBean(DispatcherServlet dispatcherServlet) {return new DispatcherServletRegistrationBean(dispatcherServlet, "/");}@Bean("/hello")public Controller controller1() {return (request, response) -> {response.getWriter().print("hello");return null;};}}@Configurationstatic class Config {@Beanpublic Bean1 bean1() {return new Bean1();}@Beanpublic Bean2 bean2(Bean1 bean1) {Bean2 bean2 = new Bean2();bean2.setBean1(bean1);return bean2;}}static class Bean1 {}static class Bean2 {private Bean1 bean1;public void setBean1(Bean1 bean1) {this.bean1 = bean1;}public Bean1 getBean1() {return bean1;}}
}

收获💡

常见的 ApplicationContext 容器实现
内嵌容器、DispatcherServlet 的创建方法、作用

3) Bean 的生命周期

一个受 Spring 管理的 bean，生命周期主要阶段有

创建：根据 bean 的构造方法或者工厂方法来创建 bean 实例对象
依赖注入：根据 @Autowired，@Value 或其它一些手段，为 bean 的成员变量填充值、建立关系
初始化：回调各种 Aware 接口，调用对象的各种初始化方法
销毁：在容器关闭时，会销毁所有单例对象（即调用它们的销毁方法）
- prototype 对象也能够销毁，不过需要容器这边主动调用

一些资料会提到，生命周期中还有一类 bean 后处理器：BeanPostProcessor，会在 bean 的初始化的前后，提供一些扩展逻辑。但这种说法是不完整的，见下面的演示1

演示1 - bean 生命周期

代码参考

package com.itheima.a03;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;/*bean 的生命周期, 以及 bean 后处理器学到了什么a. Spring bean 生命周期各个阶段b. 模板设计模式, 大流程已经固定好了, 通过接口回调(bean 后处理器)扩展*/
@SpringBootApplication
public class A03 {public static void main(String[] args) {ConfigurableApplicationContext context = SpringApplication.run(A03.class, args);context.close();}
}

package com.itheima.a03;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;@Component
public class LifeCycleBean {private static final Logger log = LoggerFactory.getLogger(LifeCycleBean.class);public LifeCycleBean() {log.debug("构造");}@Autowiredpublic void autowire(@Value("${JAVA_HOME}") String home) {log.debug("依赖注入: {}", home);}@PostConstructpublic void init() {log.debug("初始化");}@PreDestroypublic void destroy() {log.debug("销毁");}
}

package com.itheima.a03;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.stereotype.Component;@Component
public class MyBeanPostProcessor implements InstantiationAwareBeanPostProcessor, DestructionAwareBeanPostProcessor {private static final Logger log = LoggerFactory.getLogger(MyBeanPostProcessor.class);@Overridepublic void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {if (beanName.equals("lifeCycleBean"))log.debug("<<<<<< 销毁之前执行, 如 @PreDestroy");}@Overridepublic Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {if (beanName.equals("lifeCycleBean"))log.debug("<<<<<< 实例化之前执行, 这里返回的对象会替换掉原本的 bean");return null;}@Overridepublic boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {if (beanName.equals("lifeCycleBean")) {log.debug("<<<<<< 实例化之后执行, 这里如果返回 false 会跳过依赖注入阶段");
//            return false;}return true;}@Overridepublic PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {if (beanName.equals("lifeCycleBean"))log.debug("<<<<<< 依赖注入阶段执行, 如 @Autowired、@Value、@Resource");return pvs;}@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {if (beanName.equals("lifeCycleBean"))log.debug("<<<<<< 初始化之前执行, 这里返回的对象会替换掉原本的 bean, 如 @PostConstruct、@ConfigurationProperties");return bean;}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {if (beanName.equals("lifeCycleBean"))log.debug("<<<<<< 初始化之后执行, 这里返回的对象会替换掉原本的 bean, 如代理增强");return bean;}
}

创建前后的增强

postProcessBeforeInstantiation
- 这里返回的对象若不为 null 会替换掉原本的 bean，并且仅会走 postProcessAfterInitialization 流程
postProcessAfterInstantiation
- 这里如果返回 false 会跳过依赖注入阶段

依赖注入前的增强

postProcessProperties
- 如 @Autowired、@Value、@Resource

初始化前后的增强

postProcessBeforeInitialization
- 这里返回的对象会替换掉原本的 bean
- 如 @PostConstruct、@ConfigurationProperties
postProcessAfterInitialization
- 这里返回的对象会替换掉原本的 bean
- 如代理增强

销毁之前的增强

postProcessBeforeDestruction
- 如 @PreDestroy

收获💡

Spring bean 生命周期各个阶段
模板设计模式, 指大流程已经固定好了, 通过接口回调（bean 后处理器）在一些关键点前后提供扩展

演示2 - 模板方法设计模式

关键代码

public class TestMethodTemplate {public static void main(String[] args) {MyBeanFactory beanFactory = new MyBeanFactory();beanFactory.addBeanPostProcessor(bean -> System.out.println("解析 @Autowired"));beanFactory.addBeanPostProcessor(bean -> System.out.println("解析 @Resource"));beanFactory.getBean();}// 模板方法  Template Method Patternstatic class MyBeanFactory {public Object getBean() {Object bean = new Object();System.out.println("构造 " + bean);System.out.println("依赖注入 " + bean); // @Autowired, @Resourcefor (BeanPostProcessor processor : processors) {processor.inject(bean);}System.out.println("初始化 " + bean);return bean;}private List<BeanPostProcessor> processors = new ArrayList<>();public void addBeanPostProcessor(BeanPostProcessor processor) {processors.add(processor);}}static interface BeanPostProcessor {public void inject(Object bean); // 对依赖注入阶段的扩展}
}

演示3 - bean 后处理器排序

代码参考

package com.itheima.a03;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigUtils;
import org.springframework.core.Ordered;
import org.springframework.core.PriorityOrdered;
import org.springframework.core.annotation.Order;import java.util.ArrayList;
import java.util.List;/*bean 后处理的的排序*/
public class TestProcessOrder {public static void main(String[] args) {DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();AnnotationConfigUtils.registerAnnotationConfigProcessors(beanFactory);List<BeanPostProcessor> list = new ArrayList<>(List.of(new P1(), new P2(), new P3(), new P4(), new P5()));list.sort(beanFactory.getDependencyComparator());list.forEach(processor->{processor.postProcessBeforeInitialization(new Object(), "");});/*学到了什么1. 实现了 PriorityOrdered 接口的优先级最高2. 实现了 Ordered 接口与加了 @Order 注解的平级, 按数字升序3. 其它的排在最后*/}@Order(1)static class P1 implements BeanPostProcessor {private static final Logger log = LoggerFactory.getLogger(P1.class);@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {log.debug("postProcessBeforeInitialization @Order(1)");return bean;}}@Order(2)static class P2 implements BeanPostProcessor {private static final Logger log = LoggerFactory.getLogger(P2.class);@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {log.debug("postProcessBeforeInitialization @Order(2)");return bean;}}static class P3 implements BeanPostProcessor, PriorityOrdered {private static final Logger log = LoggerFactory.getLogger(P3.class);@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {log.debug("postProcessBeforeInitialization PriorityOrdered");return bean;}@Overridepublic int getOrder() {return 100;}}static class P4 implements BeanPostProcessor, Ordered {private static final Logger log = LoggerFactory.getLogger(P4.class);@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {log.debug("postProcessBeforeInitialization Ordered");return bean;}@Overridepublic int getOrder() {return 0;}}static class P5 implements BeanPostProcessor {private static final Logger log = LoggerFactory.getLogger(P5.class);@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {log.debug("postProcessBeforeInitialization");return bean;}}
}

收获💡

实现了 PriorityOrdered 接口的优先级最高
实现了 Ordered 接口与加了 @Order 注解的平级, 按数字升序
其它的排在最后

4) Bean 后处理器

演示1 - 后处理器作用

代码参考

package com.itheima.a04;import org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor;
import org.springframework.context.annotation.CommonAnnotationBeanPostProcessor;
import org.springframework.context.annotation.ContextAnnotationAutowireCandidateResolver;
import org.springframework.context.support.GenericApplicationContext;/*bean 后处理器的作用*/
public class A04 {public static void main(String[] args) {// ⬇️GenericApplicationContext 是一个【干净】的容器GenericApplicationContext context = new GenericApplicationContext();// ⬇️用原始方法注册三个 beancontext.registerBean("bean1", Bean1.class);context.registerBean("bean2", Bean2.class);context.registerBean("bean3", Bean3.class);context.registerBean("bean4", Bean4.class);context.getDefaultListableBeanFactory().setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());//@Value解析器context.registerBean(AutowiredAnnotationBeanPostProcessor.class); // @Autowired @Valuecontext.registerBean(CommonAnnotationBeanPostProcessor.class); // @Resource @PostConstruct @PreDestroyConfigurationPropertiesBindingPostProcessor.register(context.getDefaultListableBeanFactory());//@ConfigurationProperties// ⬇️初始化容器context.refresh(); // 执行beanFactory后处理器, 添加bean后处理器, 初始化所有单例System.out.println(context.getBean(Bean1.class));// ⬇️销毁容器context.close();/*学到了什么a. @Autowired 等注解的解析属于 bean 生命周期阶段(依赖注入, 初始化)的扩展功能b. 这些扩展功能由 bean 后处理器来完成*/}
}

package com.itheima.a04;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.annotation.Resource;public class Bean1 {private static final Logger log = LoggerFactory.getLogger(Bean1.class);private Bean2 bean2;@Autowiredpublic void setBean2(Bean2 bean2) {log.debug("@Autowired 生效: {}", bean2);this.bean2 = bean2;}@Autowiredprivate Bean3 bean3;@Resourcepublic void setBean3(Bean3 bean3) {log.debug("@Resource 生效: {}", bean3);this.bean3 = bean3;}private String home;@Autowiredpublic void setHome(@Value("${JAVA_HOME}") String home) {log.debug("@Value 生效: {}", home);this.home = home;}@PostConstructpublic void init() {log.debug("@PostConstruct 生效");}@PreDestroypublic void destroy() {log.debug("@PreDestroy 生效");}@Overridepublic String toString() {return "Bean1{" +"bean2=" + bean2 +", bean3=" + bean3 +", home='" + home + '\'' +'}';}
}

package com.itheima.a04;public class Bean2 {
}

package com.itheima.a04;public class Bean3 {
}

package com.itheima.a04;import org.springframework.boot.context.properties.ConfigurationProperties;/*java.home=java.version=*/
@ConfigurationProperties(prefix = "java")
public class Bean4 {private String home;private String version;public String getHome() {return home;}public void setHome(String home) {this.home = home;}public String getVersion() {return version;}public void setVersion(String version) {this.version = version;}@Overridepublic String toString() {return "Bean4{" +"home='" + home + '\'' +", version='" + version + '\'' +'}';}
}

收获💡

@Autowired 等注解的解析属于 bean 生命周期阶段（依赖注入, 初始化）的扩展功能，这些扩展功能由 bean 后处理器来完成
每个后处理器各自增强什么功能
- AutowiredAnnotationBeanPostProcessor 解析 @Autowired 与 @Value
- CommonAnnotationBeanPostProcessor 解析 @Resource、@PostConstruct、@PreDestroy
- ConfigurationPropertiesBindingPostProcessor 解析 @ConfigurationProperties
另外 ContextAnnotationAutowireCandidateResolver 负责获取 @Value 的值，解析 @Qualifier、泛型、@Lazy 等

演示2 - @Autowired bean 后处理器运行分析

代码参考

package com.itheima.a04;import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor;
import org.springframework.beans.factory.annotation.InjectionMetadata;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.ContextAnnotationAutowireCandidateResolver;
import org.springframework.core.MethodParameter;
import org.springframework.core.env.StandardEnvironment;import java.lang.reflect.Field;
import java.lang.reflect.Method;// AutowiredAnnotationBeanPostProcessor 运行分析
public class DigInAutowired {public static void main(String[] args) throws Throwable {DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();beanFactory.registerSingleton("bean2", new Bean2()); // 创建过程,依赖注入,初始化beanFactory.registerSingleton("bean3", new Bean3());beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver()); // @ValuebeanFactory.addEmbeddedValueResolver(new StandardEnvironment()::resolvePlaceholders); // ${} 的解析器// 1. 查找哪些属性、方法加了 @Autowired, 这称之为 InjectionMetadataAutowiredAnnotationBeanPostProcessor processor = new AutowiredAnnotationBeanPostProcessor();processor.setBeanFactory(beanFactory);Bean1 bean1 = new Bean1();
//        System.out.println(bean1);
//        processor.postProcessProperties(null, bean1, "bean1"); // 执行依赖注入 @Autowired @Value
//        System.out.println(bean1);//        Method findAutowiringMetadata = AutowiredAnnotationBeanPostProcessor.class.getDeclaredMethod("findAutowiringMetadata", String.class, Class.class, PropertyValues.class);
//        findAutowiringMetadata.setAccessible(true);
//        InjectionMetadata metadata = (InjectionMetadata) findAutowiringMetadata.invoke(processor, "bean1", Bean1.class, null);// 获取 Bean1 上加了 @Value @Autowired 的成员变量，方法参数信息
//        System.out.println(metadata);// 2. 调用 InjectionMetadata 来进行依赖注入, 注入时按类型查找值
//        metadata.inject(bean1, "bean1", null);
//        System.out.println(bean1);// 3. 如何按类型查找值Field bean3 = Bean1.class.getDeclaredField("bean3");DependencyDescriptor dd1 = new DependencyDescriptor(bean3, false);Object o = beanFactory.doResolveDependency(dd1, null, null, null);System.out.println(o);Method setBean2 = Bean1.class.getDeclaredMethod("setBean2", Bean2.class);DependencyDescriptor dd2 =new DependencyDescriptor(new MethodParameter(setBean2, 0), true);Object o1 = beanFactory.doResolveDependency(dd2, null, null, null);System.out.println(o1);Method setHome = Bean1.class.getDeclaredMethod("setHome", String.class);DependencyDescriptor dd3 = new DependencyDescriptor(new MethodParameter(setHome, 0), true);Object o2 = beanFactory.doResolveDependency(dd3, null, null, null);System.out.println(o2);}
}

收获💡

AutowiredAnnotationBeanPostProcessor.findAutowiringMetadata 用来获取某个 bean 上加了 @Value @Autowired 的成员变量，方法参数的信息，表示为 InjectionMetadata
InjectionMetadata 可以完成依赖注入
InjectionMetadata 内部根据成员变量，方法参数封装为 DependencyDescriptor 类型
有了 DependencyDescriptor，就可以利用 beanFactory.doResolveDependency 方法进行基于类型的查找

5) BeanFactory 后处理器

演示1 - BeanFactory 后处理器的作用

代码参考

package com.itheima.a05;import com.itheima.a05.mapper.Mapper1;
import com.itheima.a05.mapper.Mapper2;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.support.GenericApplicationContext;import java.io.IOException;/*BeanFactory 后处理器的作用*/
public class A05 {private static final Logger log = LoggerFactory.getLogger(A05.class);public static void main(String[] args) throws IOException {// ⬇️GenericApplicationContext 是一个【干净】的容器GenericApplicationContext context = new GenericApplicationContext();context.registerBean("config", Config.class);
//        context.registerBean(ConfigurationClassPostProcessor.class); // @ComponentScan @Bean @Import @ImportResource
//        context.registerBean(MapperScannerConfigurer.class, bd -> { // @MapperScanner
//            bd.getPropertyValues().add("basePackage", "com.itheima.a05.mapper");
//        });//        context.registerBean(ComponentScanPostProcessor.class); // 解析 @ComponentScancontext.registerBean(AtBeanPostProcessor.class); // 解析 @Beancontext.registerBean(MapperPostProcessor.class); // 解析 Mapper 接口// ⬇️初始化容器context.refresh();for (String name : context.getBeanDefinitionNames()) {System.out.println(name);}Mapper1 mapper1 = context.getBean(Mapper1.class);Mapper2 mapper2 = context.getBean(Mapper2.class);// ⬇️销毁容器context.close();/*学到了什么a. @ComponentScan, @Bean, @Mapper 等注解的解析属于核心容器(即 BeanFactory)的扩展功能b. 这些扩展功能由不同的 BeanFactory 后处理器来完成, 其实主要就是补充了一些 bean 定义*/}
}

package com.itheima.a05;import com.alibaba.druid.pool.DruidDataSource;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;import javax.sql.DataSource;@Configuration
@ComponentScan("com.itheima.a05.component")
public class Config {@Beanpublic Bean1 bean1() {return new Bean1();}@Beanpublic SqlSessionFactoryBean sqlSessionFactoryBean(DataSource dataSource) {SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();sqlSessionFactoryBean.setDataSource(dataSource);return sqlSessionFactoryBean;}@Bean(initMethod = "init")public DruidDataSource dataSource() {DruidDataSource dataSource = new DruidDataSource();dataSource.setUrl("jdbc:mysql://localhost:3306/test");dataSource.setUsername("root");dataSource.setPassword("root");return dataSource;}/*@Beanpublic MapperFactoryBean<Mapper1> mapper1(SqlSessionFactory sqlSessionFactory) {MapperFactoryBean<Mapper1> factory = new MapperFactoryBean<>(Mapper1.class);factory.setSqlSessionFactory(sqlSessionFactory);return factory;}@Beanpublic MapperFactoryBean<Mapper2> mapper2(SqlSessionFactory sqlSessionFactory) {MapperFactoryBean<Mapper2> factory = new MapperFactoryBean<>(Mapper2.class);factory.setSqlSessionFactory(sqlSessionFactory);return factory;}*/
}

package com.itheima.a05;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;public class Bean1 {private static final Logger log = LoggerFactory.getLogger(Bean1.class);public Bean1() {log.debug("我被 Spring 管理啦");}
}

ConfigurationClassPostProcessor 可以解析
- @ComponentScan
- @Bean
- @Import
- @ImportResource
MapperScannerConfigurer 可以解析
- Mapper 接口

收获💡

@ComponentScan, @Bean, @Mapper 等注解的解析属于核心容器（即 BeanFactory）的扩展功能
这些扩展功能由不同的 BeanFactory 后处理器来完成，其实主要就是补充了一些 bean 定义

演示2 - 模拟解析 @ComponentScan

代码参考

package com.itheima.a05;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.context.annotation.AnnotationBeanNameGenerator;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
import org.springframework.core.type.classreading.MetadataReader;
import org.springframework.stereotype.Component;import java.io.IOException;public class ComponentScanPostProcessor implements BeanDefinitionRegistryPostProcessor {@Override // context.refreshpublic void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {}@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanFactory) throws BeansException {try {ComponentScan componentScan = AnnotationUtils.findAnnotation(Config.class, ComponentScan.class);if (componentScan != null) {for (String p : componentScan.basePackages()) {System.out.println(p);// com.itheima.a05.component -> classpath*:com/itheima/a05/component/**/*.classString path = "classpath*:" + p.replace(".", "/") + "/**/*.class";System.out.println(path);CachingMetadataReaderFactory factory = new CachingMetadataReaderFactory();Resource[] resources = new PathMatchingResourcePatternResolver().getResources(path);AnnotationBeanNam	eGenerator generator = new AnnotationBeanNameGenerator();for (Resource resource : resources) {// System.out.println(resource);MetadataReader reader = factory.getMetadataReader(resource);// System.out.println("类名:" + reader.getClassMetadata().getClassName());AnnotationMetadata annotationMetadata = reader.getAnnotationMetadata();// System.out.println("是否加了 @Component:" + annotationMetadata.hasAnnotation(Component.class.getName()));// System.out.println("是否加了 @Component 派生:" + annotationMetadata.hasMetaAnnotation(Component.class.getName()));if (annotationMetadata.hasAnnotation(Component.class.getName())|| annotationMetadata.hasMetaAnnotation(Component.class.getName())) {AbstractBeanDefinition bd = BeanDefinitionBuilder.genericBeanDefinition(reader.getClassMetadata().getClassName()).getBeanDefinition();String name = generator.generateBeanName(bd, beanFactory);beanFactory.registerBeanDefinition(name, bd);}}}}} catch (IOException e) {e.printStackTrace();}}
}

收获💡

Spring 操作元数据的工具类 CachingMetadataReaderFactory
通过注解元数据（AnnotationMetadata）获取直接或间接标注的注解信息
通过类元数据（ClassMetadata）获取类名，AnnotationBeanNameGenerator 生成 bean 名
解析元数据是基于 ASM 技术

演示3 - 模拟解析 @Bean

代码参考

package com.itheima.a05;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.context.annotation.Bean;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.type.MethodMetadata;
import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
import org.springframework.core.type.classreading.MetadataReader;import java.io.IOException;
import java.util.Set;public class AtBeanPostProcessor implements BeanDefinitionRegistryPostProcessor {@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {}@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanFactory) throws BeansException {try {CachingMetadataReaderFactory factory = new CachingMetadataReaderFactory();MetadataReader reader = factory.getMetadataReader(new ClassPathResource("com/itheima/a05/Config.class"));Set<MethodMetadata> methods = reader.getAnnotationMetadata().getAnnotatedMethods(Bean.class.getName());for (MethodMetadata method : methods) {System.out.println(method);String initMethod = method.getAnnotationAttributes(Bean.class.getName()).get("initMethod").toString();BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition();builder.setFactoryMethodOnBean(method.getMethodName(), "config");builder.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_CONSTRUCTOR);if (initMethod.length() > 0) {builder.setInitMethodName(initMethod);}AbstractBeanDefinition bd = builder.getBeanDefinition();beanFactory.registerBeanDefinition(method.getMethodName(), bd);}} catch (IOException e) {e.printStackTrace();}}
}

收获💡

进一步熟悉注解元数据（AnnotationMetadata）获取方法上注解信息

演示4 - 模拟解析 Mapper 接口

代码参考

package com.itheima.a05;import org.mybatis.spring.mapper.MapperFactoryBean;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.context.annotation.AnnotationBeanNameGenerator;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.type.ClassMetadata;
import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
import org.springframework.core.type.classreading.MetadataReader;import java.io.IOException;public class MapperPostProcessor implements BeanDefinitionRegistryPostProcessor {@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanFactory) throws BeansException {try {PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();Resource[] resources = resolver.getResources("classpath:com/itheima/a05/mapper/**/*.class");AnnotationBeanNameGenerator generator = new AnnotationBeanNameGenerator();CachingMetadataReaderFactory factory = new CachingMetadataReaderFactory();for (Resource resource : resources) {MetadataReader reader = factory.getMetadataReader(resource);ClassMetadata classMetadata = reader.getClassMetadata();if (classMetadata.isInterface()) {AbstractBeanDefinition bd = BeanDefinitionBuilder.genericBeanDefinition(MapperFactoryBean.class).addConstructorArgValue(classMetadata.getClassName()).setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE).getBeanDefinition();AbstractBeanDefinition bd2 = BeanDefinitionBuilder.genericBeanDefinition(classMetadata.getClassName()).getBeanDefinition();String name = generator.generateBeanName(bd2, beanFactory);beanFactory.registerBeanDefinition(name, bd);}}} catch (IOException e) {e.printStackTrace();}}@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {}
}

收获💡

Mapper 接口被 Spring 管理的本质：实际是被作为 MapperFactoryBean 注册到容器中
Spring 的诡异做法，根据接口生成的 BeanDefinition 仅为根据接口名生成 bean 名

6) Aware 接口

演示 - Aware 接口及 InitializingBean 接口

代码参考

package com.itheima.a06;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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 A06 {private static final Logger log = LoggerFactory.getLogger(A06.class);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);//1、@Autowired失效context.registerBean("myConfig2", MyConfig2.class);//2、Aware未失效context.registerBean(AutowiredAnnotationBeanPostProcessor.class);context.registerBean(CommonAnnotationBeanPostProcessor.class);context.registerBean(ConfigurationClassPostProcessor.class);/*2. 有同学说: b、c、d 的功能用 @Autowired 就能实现啊, 为啥还要用 Aware 接口呢简单地说: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, 扩展功能会失效, 而内置功能不会失效例1: 你会发现用 Aware 注入 ApplicationContext 成功, 而 @Autowired 注入 ApplicationContext 失败*//*例2: Java 配置类在添加了 bean 工厂后处理器后,你会发现用传统接口方式的注入和初始化仍然成功, 而 @Autowired 和 @PostConstruct 的注入和初始化失败*/context.refresh(); // 1. beanFactory 后处理器,  2. 添加 bean 后处理器, 3. 初始化单例context.close();/*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, ApplicationContextb. 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 框架内部的类常用它们*/}
}

package com.itheima.a06;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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;public class MyBean implements BeanNameAware, ApplicationContextAware, InitializingBean {private static final Logger log = LoggerFactory.getLogger(MyBean.class);@Overridepublic void setBeanName(String name) {log.debug("当前bean " + this + " 名字叫:" + name);}@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {log.debug("当前bean " + this + " 容器是:" + applicationContext);}@Overridepublic void afterPropertiesSet() throws Exception {log.debug("当前bean " + this + " 初始化");}@Autowiredpublic void aaa(ApplicationContext applicationContext) {log.debug("当前bean " + this + " 使用@Autowired 容器是:" + applicationContext);}@PostConstructpublic void init() {log.debug("当前bean " + this + " 使用@PostConstruct 初始化");}
}

package com.itheima.a06;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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
public class MyConfig1 {private static final Logger log = LoggerFactory.getLogger(MyConfig1.class);@Autowiredpublic void setApplicationContext(ApplicationContext applicationContext) {log.debug("注入 ApplicationContext");}@PostConstructpublic void init() {log.debug("初始化");}@Bean //  beanFactory 后处理器public BeanFactoryPostProcessor processor1() {return beanFactory -> {log.debug("执行 processor1");};}}

package com.itheima.a06;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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
public class MyConfig2 implements InitializingBean, ApplicationContextAware {private static final Logger log = LoggerFactory.getLogger(MyConfig2.class);@Overridepublic void afterPropertiesSet() throws Exception {log.debug("初始化");}@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {log.debug("注入 ApplicationContext");}@Bean //  beanFactory 后处理器public BeanFactoryPostProcessor processor2() {return beanFactory -> {log.debug("执行 processor2");};}
}

收获💡

Aware 接口提供了一种【内置】的注入手段，例如
- BeanNameAware 注入 bean 的名字
- BeanFactoryAware 注入 BeanFactory 容器
- ApplicationContextAware 注入 ApplicationContext 容器
- EmbeddedValueResolverAware 注入 ${} 解析器
InitializingBean 接口提供了一种【内置】的初始化手段
对比
- 内置的注入和初始化不受扩展功能的影响，总会被执行
- 而扩展功能受某些情况影响可能会失效
- 因此 Spring 框架内部的类常用内置注入和初始化

配置类 @Autowired 失效分析

Java 配置类不包含 BeanFactoryPostProcessor 的情况

Java 配置类包含 BeanFactoryPostProcessor 的情况，因此要创建其中的 BeanFactoryPostProcessor 必须提前创建 Java 配置类，而此时的 BeanPostProcessor 还未准备好，导致 @Autowired 等注解失效

对应代码

@Configuration
public class MyConfig1 {private static final Logger log = LoggerFactory.getLogger(MyConfig1.class);@Autowiredpublic void setApplicationContext(ApplicationContext applicationContext) {log.debug("注入 ApplicationContext");}@PostConstructpublic void init() {log.debug("初始化");}@Bean //  ⬅️ 注释或添加 beanFactory 后处理器对应上方两种情况public BeanFactoryPostProcessor processor1() {return beanFactory -> {log.debug("执行 processor1");};}}

注意

解决方法：

用内置依赖注入和初始化取代扩展依赖注入和初始化
用静态工厂方法代替实例工厂方法，避免工厂对象提前被创建

7) 初始化与销毁

演示 - 初始化销毁顺序

代码参考

package com.itheima.a07;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;/*初始化和销毁的执行顺序*/
@SpringBootApplication
public class A07_1 {public static void main(String[] args) {ConfigurableApplicationContext context = SpringApplication.run(A07_1.class, args);context.close();/*学到了什么a. Spring 提供了多种初始化和销毁手段b. Spring 的面试有多么地卷*/}@Bean(initMethod = "init3")public Bean1 bean1() {return new Bean1();}@Bean(destroyMethod = "destroy3")public Bean2 bean2() {return new Bean2();}
}

package com.itheima.a07;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.InitializingBean;import javax.annotation.PostConstruct;public class Bean1 implements InitializingBean {private static final Logger log = LoggerFactory.getLogger(Bean1.class);@PostConstructpublic void init1() {log.debug("初始化1");}@Overridepublic void afterPropertiesSet() throws Exception {log.debug("初始化2");}public void init3() {log.debug("初始化3");}
}

package com.itheima.a07;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.DisposableBean;import javax.annotation.PreDestroy;public class Bean2 implements DisposableBean {private static final Logger log = LoggerFactory.getLogger(Bean2.class);@PreDestroypublic void destroy1() {log.debug("销毁1");}@Overridepublic void destroy() throws Exception {log.debug("销毁2");}public void destroy3() {log.debug("销毁3");}
}

package com.itheima.a07;import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;public class A07_2 {public static void main(String[] args) {DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();beanFactory.registerBeanDefinition("myBean",BeanDefinitionBuilder.genericBeanDefinition(MyBean.class).setDestroyMethodName("destroy").getBeanDefinition());System.out.println(beanFactory.getBean(MyBean.class));beanFactory.destroySingletons(); // 销毁之后, 仍可创建新的单例System.out.println(beanFactory.getBean(MyBean.class));}static class MyBean {public MyBean() {System.out.println("MyBean()");}public void destroy() {System.out.println("destroy()");}}
}

收获💡

Spring 提供了多种初始化手段，除了课堂上讲的 @PostConstruct，@Bean(initMethod) 之外，还可以实现 InitializingBean 接口来进行初始化，如果同一个 bean 用了以上手段声明了 3 个初始化方法，那么它们的执行顺序是

@PostConstruct 标注的初始化方法
InitializingBean 接口的初始化方法
@Bean(initMethod) 指定的初始化方法

与初始化类似，Spring 也提供了多种销毁手段，执行顺序为

@PreDestroy 标注的销毁方法
DisposableBean 接口的销毁方法
@Bean(destroyMethod) 指定的销毁方法

8) Scope

在当前版本的 Spring 和 Spring Boot 程序中，支持五种 Scope

singleton，容器启动时创建（未设置延迟），容器关闭时销毁
prototype，每次使用时创建，不会自动销毁，需要调用 DefaultListableBeanFactory.destroyBean(bean) 销毁
request，每次请求用到此 bean 时创建，请求结束时销毁
session，每个会话用到此 bean 时创建，会话结束时销毁
application，web 容器用到此 bean 时创建，容器停止时销毁

有些文章提到有 globalSession 这一 Scope，也是陈旧的说法，目前 Spring 中已废弃

但要注意，如果在 singleton 注入其它 scope 都会有问题，解决方法有

@Lazy
@Scope(proxyMode = ScopedProxyMode.TARGET_CLASS)
ObjectFactory
ApplicationContext.getBean

演示1 - request, session, application 作用域

代码参考

package com.itheima.a08;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;/*singleton, prototype, request, session, applicationjdk >= 9 如果反射调用 jdk 中方法jdk <= 8 不会有问题演示 request, session, application 作用域打开不同的浏览器, 刷新 http://localhost:8080/test 即可查看效果如果 jdk > 8, 运行时请添加 --add-opens java.base/java.lang=ALL-UNNAMED*/
@SpringBootApplication
public class A08 {public static void main(String[] args) {SpringApplication.run(A08.class, args);/*学到了什么a. 有几种 scopeb. 在 singleton 中使用其它几种 scope 的方法c. 其它 scope 的销毁1. 可以将通过 server.servlet.session.timeout=10s 观察 session bean 的销毁2. ServletContextScope 销毁机制疑似实现有误*/}
}

package com.itheima.a08;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Lazy;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;@RestController
public class MyController {@Lazy@Autowiredprivate BeanForRequest beanForRequest;@Lazy@Autowiredprivate BeanForSession beanForSession;@Lazy@Autowiredprivate BeanForApplication beanForApplication;@GetMapping(value = "/test", produces = "text/html")public String test(HttpServletRequest request, HttpSession session) {ServletContext sc = request.getServletContext();String sb = "<ul>" +"<li>" + "request scope:" + beanForRequest + "</li>" +"<li>" + "session scope:" + beanForSession + "</li>" +"<li>" + "application scope:" + beanForApplication + "</li>" +"</ul>";return sb;}}

package com.itheima.a08;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;import javax.annotation.PreDestroy;@Scope("request")
@Component
public class BeanForRequest {private static final Logger log = LoggerFactory.getLogger(BeanForRequest.class);@PreDestroypublic void destroy() {log.debug("destroy");}}

package com.itheima.a08;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;import javax.annotation.PreDestroy;@Scope("session")
@Component
public class BeanForSession {private static final Logger log = LoggerFactory.getLogger(BeanForSession.class);@PreDestroypublic void destroy() {log.debug("destroy");}
}

package com.itheima.a08;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;import javax.annotation.PreDestroy;@Scope("application")
@Component
public class BeanForApplication {private static final Logger log = LoggerFactory.getLogger(BeanForApplication.class);@PreDestroypublic void destroy() {log.debug("destroy");}
}

打开不同的浏览器, 刷新 http://localhost:8080/test 即可查看效果
如果 jdk > 8, 运行时请添加 --add-opens java.base/java.lang=ALL-UNNAMED

收获💡

有几种 scope
在 singleton 中使用其它几种 scope 的方法
其它 scope 的销毁时机
- 可以将通过 server.servlet.session.timeout=30s 观察 session bean 的销毁
- ServletContextScope 销毁机制疑似实现有误

分析 - singleton 注入其它 scope 失效

以单例注入多例为例

有一个单例对象 E

@Component
public class E {private static final Logger log = LoggerFactory.getLogger(E.class);private F f;public E() {log.info("E()");}@Autowiredpublic void setF(F f) {this.f = f;log.info("setF(F f) {}", f.getClass());}public F getF() {return f;}
}

要注入的对象 F 期望是多例

@Component
@Scope("prototype")
public class F {private static final Logger log = LoggerFactory.getLogger(F.class);public F() {log.info("F()");}
}

测试

E e = context.getBean(E.class);
F f1 = e.getF();
F f2 = e.getF();
System.out.println(f1);
System.out.println(f2);

输出

com.itheima.demo.cycle.F@6622fc65
com.itheima.demo.cycle.F@6622fc65

发现它们是同一个对象，而不是期望的多例对象

对于单例对象来讲，依赖注入仅发生了一次，后续再没有用到多例的 F，因此 E 用的始终是第一次依赖注入的 F

解决

仍然使用 @Lazy 生成代理
代理对象虽然还是同一个，但当每次使用代理对象的任意方法时，由代理创建新的 f 对象

@Component
public class E {@Autowired@Lazypublic void setF(F f) {this.f = f;log.info("setF(F f) {}", f.getClass());}// ...
}

注意

@Lazy 加在也可以加在成员变量上，但加在 set 方法上的目的是可以观察输出，加在成员变量上就不行了
@Autowired 加在 set 方法的目的类似

输出

E: setF(F f) class com.itheima.demo.cycle.F$$EnhancerBySpringCGLIB$$8b54f2bc
F: F()
com.itheima.demo.cycle.F@3a6f2de3
F: F()
com.itheima.demo.cycle.F@56303b57

从输出日志可以看到调用 setF 方法时，f 对象的类型是代理类型

演示2 - 4种解决方法

代码参考

package com.itheima.a08.sub;import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Component;@Component
public class E {@Lazy@Autowiredprivate F1 f1;@Autowiredprivate F2 f2;@Autowiredprivate ObjectFactory<F3> f3;@Autowiredprivate ApplicationContext context;public F1 getF1() {return f1;}public F2 getF2() {return f2;}public F3 getF3() {return f3.getObject();}public F4 getF4() {return context.getBean(F4.class);}
}

package com.itheima.a08.sub;import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;@Scope("prototype")
@Component
public class F1 {
}

package com.itheima.a08.sub;import org.springframework.context.annotation.Scope;
import org.springframework.context.annotation.ScopedProxyMode;
import org.springframework.stereotype.Component;@Scope(value = "prototype", proxyMode = ScopedProxyMode.TARGET_CLASS)
@Component
public class F2 {
}

package com.itheima.a08.sub;import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;@Scope("prototype")
@Component
public class F3 {
}

package com.itheima.a08.sub;import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;@Scope("prototype")
@Component
public class F4 {
}

如果 jdk > 8, 运行时请添加 --add-opens java.base/java.lang=ALL-UNNAMED

收获💡

单例注入其它 scope 的四种解决方法
- @Lazy
- @Scope(value = “prototype”, proxyMode = ScopedProxyMode.TARGET_CLASS)
- ObjectFactory
- ApplicationContext
解决方法虽然不同，但理念上殊途同归: 都是推迟其它 scope bean 的获取

文章目录

容器与 bean

1) 容器接口

演示1 - BeanFactory 与 ApplicationContext 的区别

关键代码参考

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演示2 - 国际化

2) 容器实现

演示1 - DefaultListableBeanFactory

代码参考

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演示2 - 常见 ApplicationContext 实现

代码参考

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3) Bean 的生命周期

演示1 - bean 生命周期

代码参考

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演示2 - 模板方法设计模式

关键代码

演示3 - bean 后处理器排序

代码参考

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4) Bean 后处理器

演示1 - 后处理器作用

代码参考

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演示2 - @Autowired bean 后处理器运行分析

代码参考

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5) BeanFactory 后处理器

演示1 - BeanFactory 后处理器的作用

代码参考

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演示2 - 模拟解析 @ComponentScan

代码参考

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演示3 - 模拟解析 @Bean

代码参考

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演示4 - 模拟解析 Mapper 接口

代码参考

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6) Aware 接口

演示 - Aware 接口及 InitializingBean 接口

代码参考

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配置类 @Autowired 失效分析

7) 初始化与销毁

演示 - 初始化销毁顺序

代码参考

收获💡

8) Scope

演示1 - request, session, application 作用域

代码参考

收获💡

分析 - singleton 注入其它 scope 失效

演示2 - 4种解决方法

代码参考

收获💡

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