Spring Boot 启动源码解析系列六：执行启动方法一

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public ConfigurableApplicationContext (String... args) {
    
    StopWatch stopWatch = new StopWatch();
    // 开始执行，记录开始时间
    stopWatch.start();

    ConfigurableApplicationContext context = null;
    FailureAnalyzers analyzers = null;
    this.configureHeadlessProperty();
    
    // 获取 SpringApplicationRunListener 实现类，实际只有 EventPublishingRunListener 一个实现类
    SpringApplicationRunListeners listeners = this.getRunListeners(args);
    // ApplicationStartedEvent 事件监听器执行监听
    listeners.starting();

    try {
        // 实例化应用程序参数持有类
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
        // 实例化容器环境配置信息
        ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);

        // 打印 Banner
        Banner printedBanner = this.printBanner(environment);

        // 实例化 Spring ApplicationContext 
        context = this.createApplicationContext();
        new FailureAnalyzers(context);
        this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
        this.refreshContext(context);
        this.afterRefresh(context, applicationArguments);

        // 
        listeners.finished(context, (Throwable)null);
        stopWatch.stop();
        if (this.logStartupInfo) {
            (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
        }

        return context;
    } catch (Throwable var9) {
        this.handleRunFailure(context, listeners, (FailureAnalyzers)analyzers, var9);
        throw new IllegalStateException(var9);
    }
}

核心步骤一：启动 SpringApplicationRunListener

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SpringApplicationRunListeners listeners = this.getRunListeners(args);
listeners.starting();

SpringApplicationRunListener 接口：

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public interface SpringApplicationRunListener {
    void starting();

    void environmentPrepared(ConfigurableEnvironment var1);

    void contextPrepared(ConfigurableApplicationContext var1);

    void contextLoaded(ConfigurableApplicationContext var1);

    void finished(ConfigurableApplicationContext var1, Throwable var2);
}

SpringApplicationRunListener 接口目前只有 EventPublishingRunListener 一个实现类。

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private SpringApplicationRunListeners getRunListeners(String[] args) {
    Class<?>[] types = new Class[]{SpringApplication.class, String[].class};
    return new SpringApplicationRunListeners(logger, this.getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
}

同理也是实例化 SpringApplicationRunListener 接口实现类，最终实际是调用 EventPublishingRunListener 的 starting() 方法：

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public void starting() {
    this.initialMulticaster.multicastEvent(new ApplicationStartedEvent(this.application, this.args));
}

最终调用：

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public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) {
    ResolvableType type = eventType != null ? eventType : this.resolveDefaultEventType(event);
    Iterator var4 = this.getApplicationListeners(event, type).iterator();

    while(var4.hasNext()) {
        final ApplicationListener<?> listener = (ApplicationListener)var4.next();
        Executor executor = this.getTaskExecutor();
        if (executor != null) {
            executor.execute(new Runnable() {
                public void () {
                    SimpleApplicationEventMulticaster.this.invokeListener(listener, event);
                }
            });
        } else {
            this.invokeListener(listener, event);
        }
    }

}

SpringApplicationRunListener 会被构建为 AppicationEvent，然后被 ApplicationEventMulticaster 广播，最后转变为 ApplicationListener。

这中间比较复杂，看的也不是特别的深入，后续继续深入分析。

原文:大专栏  Spring Boot 启动源码解析系列六：执行启动方法一


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