SpringBoot 从入门到光头 —— 第十章 原理解析

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1. SpringBoot 原理

Spring 原理、Spring 注解、SpringMVC 原理、自动配置原理、SpringBoot 原理

2. SpringBoot 自动过程

• 创建 SpringApplication

  • 保存一些信息
  • 判定当前应用的类型 ClassUtils，一般情况下是 Servlet
  • bootstrappers：初始启动引导器（List<Bootstrapper>）：去spring.factories 文件中查找 org.springframework.boot.Bootstrapper
  • 查找 ApplicationContextInitializer：去 spring.factories 中查找 ApplicationContextInitializer
    • List<ApplicationContextInitializer<?>> initializers
  • 查找 ApplicationListener：应用监听器，去 spring.factories 中查找 ApplicationListener
    • List<ApplicationListener<?>> listeners

• 运行 SpringApplication

  • StopWatch

  • 记录应用的启动时间

  • 创建引导上下文（Context 环境）createBootstrapContext()

    ​ org.springframework.boot.BootstrapRegistryInitializer

    /**
     * Callback interface that can be used to initialize a {@link BootstrapRegistry} before it
     * is used.
     *
     * @author Phillip Webb
     * @since 2.4.5
     * @see SpringApplication#addBootstrapRegistryInitializer(BootstrapRegistryInitializer)
     * @see BootstrapRegistry
     */
    @FunctionalInterface
    public interface BootstrapRegistryInitializer {
        /**
         * Initialize the given {@link BootstrapRegistry} with any required registrations.
         * @param registry the registry to initialize
         */
        void initialize(BootstrapRegistry registry);
    }
    

    • 获取到所有之前的 bootstrappers 挨个执行 intitialize() 方法来完成对引导启动器上下文环境设置

  • 让当前应用进入 headless 模式，java.awt.headless

  • 获取所有 RunListener（运行监听器）【为了方便所有 Listener 进行事件感知】

    • getSpringFactoriesInstances 在 spring.factories 找 SpringApplicationRunListener

      

  • 遍历 SpringApplicationRunListener 调用 starting 方法

    • 相当于通知所有感兴趣系统正在启动过程的人，项目正在 starting

  • 保存命令行参数 ApplicationArguments

  • 准备环境 prepareEnvironment()

    • 返回或者创建基础环境信息对象，StandardServletEnvironment
    • 配置环境信息对象
      • 读取所有的配置源的配置属性值
    • 绑定环境信息
    • 监听器调用 listener.environmentPrepared()，通知所有的监听器当前环境准备完成

  • 创建 IOC 容器（createApplicationContext()）

    • 根据项目类型（Servlet）创建容器
    • 在当前会话中创建 AnnotationConfigServletWebServerApplicationContext

  • 准备 ApplicationContext IOC 容器的基本信息 prepareContext()

    • 保存环境信息

    • IOC 容器的后置处理流程

    • 应用初始化器：applyInitializers

      • 遍历所有的 ApplicationContextInitializer 调用 initialize() 来对 IOC 容器进行初始化扩展功能

        

      • 遍历所有的 Listener 调用 contextPrepared()，EventPublishRunListenr，通知所有的监听器 contextPrepared()

    • 所有的监听器调用 contextLoaded() 通知所有的监听器 contextLoaded()

  • 刷新 IOC 容器 refreshContext()

    • 创建容器中的所有组件（Spring 注解）

  • 容器刷新完成后的工作：afterRefresh()

  • 所有监听器调用 listeners.started(context)，通知所有的监听器 started

  • 调用所有 runners：callRunners()

  • • • 获取容器中的 ApplicationRunner
        • 获取容器中的 CommandLineRunner

  • • • 合并所有 runner 并且按照 @Order 进行排序

        • 遍历所有的 runner，调用 run() 方法

          ​ org.springframework.boot.ApplicationRunner

          /**
           * Interface used to indicate that a bean should <em>run</em> when it is contained within
           * a &#123;@link SpringApplication&#125;. Multiple &#123;@link ApplicationRunner&#125; beans can be defined
           * within the same application context and can be ordered using the &#123;@link Ordered&#125;
           * interface or &#123;@link Order @Order&#125; annotation.
           *
           * @author Phillip Webb
           * @since 1.3.0
           * @see CommandLineRunner
           */
          @FunctionalInterface
          public interface ApplicationRunner &#123;
              /**
               * Callback used to run the bean.
               * @param args incoming application arguments
               * @throws Exception on error
               */
              void run(ApplicationArguments args) throws Exception;
          &#125;
          

          ​ org.springframework.boot.CommandLineRunner

          /**
           * Interface used to indicate that a bean should <em>run</em> when it is contained within
           * a &#123;@link SpringApplication&#125;. Multiple &#123;@link CommandLineRunner&#125; beans can be defined
           * within the same application context and can be ordered using the &#123;@link Ordered&#125;
           * interface or &#123;@link Order @Order&#125; annotation.
           * <p>
           * If you need access to &#123;@link ApplicationArguments&#125; instead of the raw String array
           * consider using &#123;@link ApplicationRunner&#125;.
           *
           * @author Dave Syer
           * @since 1.0.0
           * @see ApplicationRunner
           */
          @FunctionalInterface
          public interface CommandLineRunner &#123;
              /**
               * Callback used to run the bean.
               * @param args incoming main method arguments
               * @throws Exception on error
               */
              void run(String... args) throws Exception;
          &#125;
          

  • 如果以上有异常：

    • 调用 Listener 的 failed() 方法

  • 调用所有监听器的 running() 方法 listeners.running(context)，通知所有的监听器 running

  • running() 如果有问题，继续通知 failed，调用所有 Listener 的 failed() 方法，通知所有的监听器 failed

3. Application Events 和 Liateners

https://docs.spring.io/spring-boot/docs/current/reference/html/spring-boot-features.html#boot-features-application-events-and-listeners

• ApplicationContextInitializer
• ApplicationListener
• SpringAppliactionRunListener

示例代码：

com.gregperlinli.boot.listener.MyApplicationContextInitializer

/**
 * @author gregPerlinLi
 * @since 2021-11-29
 */
public class MyApplicationContextInitializer implements ApplicationContextInitializer {
    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        System.out.println("MyApplicationContextInitializer.initialize ... ");
    }
}

com.gregperlinli.boot.listener.MyApplicationListener

/**
 * @author gregPerlinLi
 * @since 2021-11-29
 */
public class MyApplicationListener implements ApplicationListener {
    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        System.out.println("MyApplicationListener.onApplicationEvent ... ");
    }
}

com.gregperlinli.boot.listener.MySpringApplicationRunListener

/**
 * @author gregPerlinLi
 * @since 2021-11-29
 */
public class MySpringApplicationRunListener implements SpringApplicationRunListener {
    private SpringApplication application;
  
    public MySpringApplicationRunListener(SpringApplication application, String[] args) {
        this.application = application;
    }
    @Override
    public void starting(ConfigurableBootstrapContext bootstrapContext) {
        System.out.println("MySpringApplicationRunListener.starting ... ");
    }
    @Override
    public void environmentPrepared(ConfigurableBootstrapContext bootstrapContext, ConfigurableEnvironment environment) {
        System.out.println("MySpringApplicationRunListener.environmentPrepared ... ");
    }
    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("MySpringApplicationRunListener.contextPrepared ... ");
    }
    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("MySpringApplicationRunListener.contextLoaded ... ");
    }
    @Override
    public void started(ConfigurableApplicationContext context, Duration timeTaken) {
        System.out.println("MySpringApplicationRunListener.started ... ");
    }
    @Override
    public void ready(ConfigurableApplicationContext context, Duration timeTaken) {
        System.out.println("MySpringApplicationRunListener.ready ... ");
    }
    @Override
    public void failed(ConfigurableApplicationContext context, Throwable exception) {
        System.out.println("MySpringApplicationRunListener.failed ... ");
    }
}

spring.factories

org.springframework.context.ApplicationContextInitializer=\
  com.gregperlinli.boot.listener.MyApplicationContextInitializer

org.springframework.context.ApplicationListener=\
  com.gregperlinli.boot.listener.MyApplicationListener

org.springframework.boot.SpringApplicationRunListener=\
  com.gregperlinli.boot.listener.MySpringApplicationRunListener

4. ApplicationRunner 和 CommandLineRunner

示例代码：

com.gregperlinli.boot.listener.MyApplicationRunner

/**
 * @author gregPerlinLi
 * @since 2021-11-29
 */
@Order(1)
@Component
public class MyApplicationRunner implements ApplicationRunner {
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("MyApplicationRunner.run ... ");
    }
}

com.gregperlinli.boot.listener.MyCommandLineRunner

/**
 * Application startup does a one-time thing
 *
 * @author gregPerlinLi
 * @since 2021-11-29
 */
@Order(2)
@Component
public class MyCommandLineRunner implements CommandLineRunner {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("MyCommandLineRunner.run ... ");
    }
}

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