Spring boot 2.5.x 啟動(dòng)流程源碼分析

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
    this.resourceLoader = resourceLoader;
    Assert.notNull(primarySources, "PrimarySources must not be null");
    //用LinkedHashSet將主類(lèi)給保存了起來(lái)
    this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
    //對(duì)項(xiàng)目的類(lèi)型做一個(gè)判斷，WebApplicationType枚舉類(lèi)中有三種，后邊這個(gè)方法就是一個(gè)判斷方法
    this.webApplicationType = WebApplicationType.deduceFromClasspath();
    //這里將對(duì)象注冊(cè)表初始化，然后保存起來(lái)
    this.bootstrapRegistryInitializers = getBootstrapRegistryInitializersFromSpringFactories();
    //這個(gè)是要通過(guò) SPI 機(jī)制去掃描 META-INF/spring.factories ，加載 ApplicationContextInitializer 接口的實(shí)例，這個(gè)類(lèi)當(dāng)springboot上下文Context初始化完成后會(huì)調(diào)用
    setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
    //同上,這個(gè) ApplicationListener 類(lèi)當(dāng)springboot啟動(dòng)時(shí)事件change后都會(huì)觸發(fā)
    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    //堆棧跟蹤判斷方法是否是 main 
    this.mainApplicationClass = deduceMainApplicationClass();
  }

org.springframework.context.ApplicationContextInitializer=\
hasaki_w_c.demo.listener.MyApplicationContextInitializer

org.springframework.context.ApplicationListener=\
hasaki_w_c.demo.listener.MyApplicationListener

public ConfigurableApplicationContext run(String... args) {
    //啟動(dòng)一個(gè) StopWatch 計(jì)時(shí)器(spring 5.2以后，運(yùn)行時(shí)間就以納秒進(jìn)行跟蹤了)
    StopWatch stopWatch = new StopWatch();
    //計(jì)時(shí)器啟動(dòng)
    stopWatch.start();
    DefaultBootstrapContext bootstrapContext = createBootstrapContext();
    ConfigurableApplicationContext context = null;
    //設(shè)置環(huán)境變量
    configureHeadlessProperty();
    //獲取事件監(jiān)聽(tīng)器SpringApplicationRunListener類(lèi)型
    SpringApplicationRunListeners listeners = getRunListeners(args);
    //入?yún)⑹巧舷挛膶?duì)象和前邊new SpringApplication最后那個(gè)堆棧跟蹤的返回值，這里就啟動(dòng)了監(jiān)聽(tīng)器
    listeners.starting(bootstrapContext, this.mainApplicationClass);
    try {
      //然后把參數(shù)封裝成提供運(yùn)行SpringApplication 的參數(shù)的訪問(wèn)的這個(gè)接口對(duì)象，通過(guò)這個(gè)接口的默認(rèn)實(shí)現(xiàn)類(lèi)進(jìn)行的
      ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
      //然后把環(huán)境和上下文以及上邊它剛剛封裝好的那個(gè)參數(shù)訪問(wèn)對(duì)象綁定
      ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
      //對(duì)環(huán)境的值判斷，以及設(shè)置
      configureIgnoreBeanInfo(environment);
      //然后打印 banner （就是那個(gè)啟動(dòng)后的控制臺(tái)比較大的那個(gè)spring boot）（終于直到那個(gè)圖形哪里來(lái)的了）
      Banner printedBanner = printBanner(environment);
      //創(chuàng)建上下文，根據(jù)項(xiàng)目類(lèi)型創(chuàng)建上下文，這個(gè)創(chuàng)建的方法里是要用到new 時(shí)候那個(gè) WebApplicationType
      context = createApplicationContext();
      //保存使用ApplicationStartup來(lái)標(biāo)記應(yīng)用程序啟動(dòng)期間的步驟，以及記錄一些收集到的執(zhí)行上下文或其處理時(shí)間的數(shù)據(jù)
      context.setApplicationStartup(this.applicationStartup);
      //準(zhǔn)備上下文，將前邊的幾個(gè)變量全丟進(jìn)這個(gè)方法的參數(shù)里
      prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
      //這個(gè)就是非常重要的東西了，是spring 的啟動(dòng)代碼，這里邊掃描并初始化 bean 了，然后 spring boot 內(nèi)嵌的web 容器也在這里邊被啟動(dòng)，需要進(jìn)去細(xì)看了。
      refreshContext(context);
      //進(jìn)去看了以下發(fā)現(xiàn)啥也沒(méi)干
      afterRefresh(context, applicationArguments);
      //停止計(jì)時(shí)器
      stopWatch.stop();
      if (this.logStartupInfo) {
        //啟動(dòng)時(shí)記錄程序的信息，并打印日志
        new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
      }
      //執(zhí)行ApplicationRunListeners中的started()方法
      listeners.started(context);
      //執(zhí)行兩個(gè)Runner（ApplicationRunner和CommandLineRunner）
      callRunners(context, applicationArguments);
    }
    catch (Throwable ex) {
      //處理運(yùn)行失敗
      handleRunFailure(context, ex, listeners);
      throw new IllegalStateException(ex);
    }

    try {
      //執(zhí)行ApplicationRunListeners中的started()方法
      listeners.running(context);
    }
    catch (Throwable ex) {
      //處理運(yùn)行失敗
      handleRunFailure(context, ex, null);
      throw new IllegalStateException(ex);
    }
    return context;
  }

public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
      StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

      // Prepare this context for refreshing.
      prepareRefresh();

      // Tell the subclass to refresh the internal bean factory.
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      // Prepare the bean factory for use in this context.
      prepareBeanFactory(beanFactory);

      try {
        // Allows post-processing of the bean factory in context subclasses.
        postProcessBeanFactory(beanFactory);

        StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
        // Invoke factory processors registered as beans in the context.
        invokeBeanFactoryPostProcessors(beanFactory);

        // Register bean processors that intercept bean creation.
        registerBeanPostProcessors(beanFactory);
        beanPostProcess.end();

        // Initialize message source for this context.
        initMessageSource();

        // Initialize event multicaster for this context.
        initApplicationEventMulticaster();

        // Initialize other special beans in specific context subclasses.
        //這個(gè)重點(diǎn)看一下
        onRefresh();

        // Check for listener beans and register them.
        registerListeners();

        // Instantiate all remaining (non-lazy-init) singletons.
        finishBeanFactoryInitialization(beanFactory);

        // Last step: publish corresponding event.
        finishRefresh();
      }

      catch (BeansException ex) {
        if (logger.isWarnEnabled()) {
          logger.warn("Exception encountered during context initialization - " +
              "cancelling refresh attempt: " + ex);
        }

        // Destroy already created singletons to avoid dangling resources.
        destroyBeans();

        // Reset 'active' flag.
        cancelRefresh(ex);

        // Propagate exception to caller.
        throw ex;
      }

      finally {
        // Reset common introspection caches in Spring's core, since we
        // might not ever need metadata for singleton beans anymore...
        resetCommonCaches();
        contextRefresh.end();
      }
    }
  }