Spring Boot - Application Events 的发布顺序_ApplicationContextInitializedEvent

package com.artisan.event;

import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Configuration;

/**
 * @author 小工匠
 * @version 1.0
 * @mark: show me the code , change the world
 */
@Configuration
public class ApplicationContextNewInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {

    /**
     * ApplicationContextInitializedEvent 在准备应用程序上下文期间，但在将 Bean 定义加载到 Spring 容器之前。
     * <p>
     * 此事件提供了在初始化 Bean 之前执行任务的机会，例如注册属性源和基于上下文环境激活 Bean 等。
     * <p>
     * <p>
     * 为了处理该 ApplicationContextInitializedEvent 事件，
     * 我们可以通过实现 ApplicationContextInitializer ConfigurableApplicationContext 作为泛型类型的接口来为应用程序创建一个额外的初始值设定项。
     * 可以在主应用程序类中手动添加此初始值设定项。
     * <p>
     * <p>
     * 当我们运行 Spring Boot 应用程序时， ApplicationContextNewInitializer 将调用 这将允许我们在加载任何 Bean 定义之前根据需要执行任务
     * new SpringApplicationBuilder(EventsApplication.class).initializers(new ApplicationContextNewInitializer()).run(args);
     *
     * @param applicationContext the application to configure
     */

    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        System.out.println("--------------------> Handling ApplicationContextInitializedEvent here!");
    }
}

@SpringBootApplication
public class LifeCycleApplication {

    /**
     * 除了手工add , 在 META-INF下面 的 spring.factories 里增加
     * org.springframework.context.ApplicationListener=自定义的listener 也可以
     *
     * @param args
     */
    public static void main(String[] args) {
      
       new SpringApplicationBuilder(LifeCycleApplication.class)
               .initializers(new ApplicationContextNewInitializer()).run(args)
    }


}

org.springframework.context.ApplicationContextInitializer=\
com.artisan.event.ApplicationContextNewInitializer

SpringApplication.run(LifeCycleApplication.class, args);

public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
		return run(new Class<?>[] { primarySource }, args);
	}

public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
		return new SpringApplication(primarySources).run(args);
	}

	/**
	 * Create a new {@link SpringApplication} instance. The application context will load
	 * beans from the specified primary sources (see {@link SpringApplication class-level}
	 * documentation for details. The instance can be customized before calling
	 * {@link #run(String...)}.
	 * @param resourceLoader the resource loader to use
	 * @param primarySources the primary bean sources
	 * @see #run(Class, String[])
	 * @see #setSources(Set)
	 */
	@SuppressWarnings({ "unchecked", "rawtypes" })
	public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
		this.resourceLoader = resourceLoader;
		Assert.notNull(primarySources, "PrimarySources must not be null");
		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
		this.webApplicationType = WebApplicationType.deduceFromClasspath();
		this.bootstrappers = new ArrayList<>(getSpringFactoriesInstances(Bootstrapper.class));
		setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
		this.mainApplicationClass = deduceMainApplicationClass();
	}

// 开始启动Spring应用程序
public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch(); // 创建一个计时器
    stopWatch.start(); // 开始计时
    
    DefaultBootstrapContext bootstrapContext = createBootstrapContext(); // 创建引导上下文
    ConfigurableApplicationContext context = null; // Spring应用上下文，初始化为null
    
    configureHeadlessProperty(); // 配置无头属性（如：是否在浏览器中运行）

    SpringApplicationRunListeners listeners = getRunListeners(args); // 获取运行监听器
    listeners.starting(bootstrapContext, this.mainApplicationClass); // 通知监听器启动过程开始
    
    try {
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); // 创建应用参数
        ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments); // 预备环境
        configureIgnoreBeanInfo(environment); // 配置忽略BeanInfo
        
        Banner printedBanner = printBanner(environment); // 打印Banner
        context = createApplicationContext(); // 创建应用上下文
        context.setApplicationStartup(this.applicationStartup); // 设置应用启动状态
        
        prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner); // 准备上下文
        refreshContext(context); // 刷新上下文，执行Bean的生命周期
        afterRefresh(context, applicationArguments); // 刷新后的操作
        
        stopWatch.stop(); // 停止计时
        if (this.logStartupInfo) { // 如果需要记录启动信息
            new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch); // 记录启动信息
        }
        listeners.started(context); // 通知监听器启动完成
        
        callRunners(context, applicationArguments); // 调用Runner
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, listeners); // 处理运行失败
        throw new IllegalStateException(ex); // 抛出异常
    }

    try {
        listeners.running(context); // 通知监听器运行中
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, null); // 处理运行失败
        throw new IllegalStateException(ex); // 抛出异常
    }
    return context; // 返回应用上下文
}

   prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);

private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context,
        ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
        ApplicationArguments applicationArguments, Banner printedBanner) {
    // 将环境变量设置到Spring上下文
    context.setEnvironment(environment);
    // 对Spring上下文进行后处理
    postProcessApplicationContext(context);
    // 应用初始izers，这些是对Spring上下文进行额外配置的组件
    applyInitializers(context);
    // 通知监听器，上下文已准备好
    listeners.contextPrepared(context);
    // 关闭bootstrap上下文
    bootstrapContext.close(context);
    // 如果需要记录启动信息
    if (this.logStartupInfo) {
        // 记录启动信息，并判断是否为根上下文
        logStartupInfo(context.getParent() == null);
        // 记录Spring Boot的配置信息
        logStartupProfileInfo(context);
    }
    // 注册Spring Boot特定的单例bean
    ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
    // 注册应用启动参数为单例bean，键为'springApplicationArguments'
    beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
    // 如果有打印的Banner，将其注册为单例bean，键为'springBootBanner'
    if (printedBanner != null) {
        beanFactory.registerSingleton("springBootBanner", printedBanner);
    }
    // 如果bean工厂是DefaultListableBeanFactory的实例，设置是否允许Bean定义覆盖
    if (beanFactory instanceof DefaultListableBeanFactory) {
        ((DefaultListableBeanFactory) beanFactory)
                .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
    }
    // 如果设置了懒惰初始化，添加一个后处理器
    if (this.lazyInitialization) {
        context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
    }
    // 加载所有源，通常是Bean定义的来源
    Set<Object> sources = getAllSources();
    // 断言源集合不为空，这些源将被加载到Spring上下文中
    Assert.notEmpty(sources, "Sources must not be empty");
    // 使用源数组加载Spring上下文
    load(context, sources.toArray(new Object[0]));
    // 通知监听器，上下文已加载
    listeners.contextLoaded(context);
}

		protected void applyInitializers(ConfigurableApplicationContext context) {
		for (ApplicationContextInitializer initializer : getInitializers()) {
			Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(),
					ApplicationContextInitializer.class);
			Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
			initializer.initialize(context);
		}
	}

     @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        System.out.println("--------------------> Handling ApplicationContextInitializedEvent here!");
    }

listeners.contextPrepared(context);	

	@Override
	public void contextPrepared(ConfigurableApplicationContext context) {
		this.initialMulticaster
				.multicastEvent(new ApplicationContextInitializedEvent(this.application, this.args, context));
	}

	@Override
	public void multicastEvent(ApplicationEvent event) {
		multicastEvent(event, resolveDefaultEventType(event));
	}

@Override
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
    // 如果eventType不为null，则直接使用它；否则，使用resolveDefaultEventType方法来解析事件的默认类型。
    ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
    
    // 获取一个线程池执行器，它用于异步执行监听器调用。
    Executor executor = getTaskExecutor();
    
    // 获取所有对应该事件类型的监听器。
    for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
        // 如果执行器不为null，则使用它来异步执行监听器调用；
        // 否则，直接同步调用监听器。
        if (executor != null) {
            executor.execute(() -> invokeListener(listener, event));
        }
        else {
            invokeListener(listener, event);
        }
    }
}

private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
		try {
			listener.onApplicationEvent(event);
		}
		catch (ClassCastException ex) {
			......
		}
	}