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@SpringBootApplicationpublic class MyApplication { public static void main(String[] args) { SpringApplication.run(MyApplication.class, args); }}

public SpringApplication(Object... sources) { initialize(sources); // sources目前是一个MyApplication的class对象}
private void initialize(Object[] sources) { if (sources != null && sources.length > 0) { this.sources.addAll(Arrays.asList(sources)); // 把sources设置到SpringApplication的sources属性中，目前只是一个MyApplication类对象 } this.webEnvironment = deduceWebEnvironment(); // 判断是否是web程序(javax.servlet.Servlet和org.springframework.web.context.ConfigurableWebApplicationContext都必须在类加载器中存在)，并设置到webEnvironment属性中 // 从spring.factories文件中找出key为ApplicationContextInitializer的类并实例化后设置到SpringApplication的initializers属性中。这个过程也就是找出所有的应用程序初始化器 setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); // 从spring.factories文件中找出key为ApplicationListener的类并实例化后设置到SpringApplication的listeners属性中。这个过程就是找出所有的应用程序事件监听器 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); // 找出main类，这里是MyApplication类 this.mainApplicationClass = deduceMainApplicationClass();} 

public interface ApplicationContextInitializer<C extends ConfigurableApplicationContext> { void initialize(C applicationContext);}

public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); // 构造一个任务执行观察器 stopWatch.start(); // 开始执行，记录开始时间 ConfigurableApplicationContext context = null; configureHeadlessProperty(); // 获取SpringApplicationRunListeners，内部只有一个EventPublishingRunListener SpringApplicationRunListeners listeners = getRunListeners(args); // 上面分析过，会封装成SpringApplicationEvent事件然后广播出去给SpringApplication中的listeners所监听 // 这里接受ApplicationStartedEvent事件的listener会执行相应的操作 listeners.started(); try { // 构造一个应用程序参数持有类 ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); // 创建Spring容器 context = createAndRefreshContext(listeners, applicationArguments); // 容器创建完成之后执行额外一些操作 afterRefresh(context, applicationArguments); // 广播出ApplicationReadyEvent事件给相应的监听器执行 listeners.finished(context, null); stopWatch.stop(); // 执行结束，记录执行时间 if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } return context; // 返回Spring容器 } catch (Throwable ex) { handleRunFailure(context, listeners, ex); // 这个过程报错的话会执行一些异常操作、然后广播出ApplicationFailedEvent事件给相应的监听器执行 throw new IllegalStateException(ex); }}

private ConfigurableApplicationContext createAndRefreshContext( SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) { ConfigurableApplicationContext context; // 定义Spring容器 // 创建应用程序的环境信息。如果是web程序，创建StandardServletEnvironment；否则，创建StandardEnvironment ConfigurableEnvironment environment = getOrCreateEnvironment(); // 配置一些环境信息。比如profile，命令行参数 configureEnvironment(environment, applicationArguments.getSourceArgs()); // 广播出ApplicationEnvironmentPreparedEvent事件给相应的监听器执行 listeners.environmentPrepared(environment); // 环境信息的校对 if (isWebEnvironment(environment) && !this.webEnvironment) { environment = convertToStandardEnvironment(environment); }
 if (this.bannerMode != Banner.Mode.OFF) { // 是否在控制台上打印自定义的banner printBanner(environment); }
 // Create, load, refresh and run the ApplicationContext context = createApplicationContext(); // 创建Spring容器 context.setEnvironment(environment); // 设置Spring容器的环境信息 postProcessApplicationContext(context); // 回调方法，Spring容器创建之后做一些额外的事 applyInitializers(context); // SpringApplication的的初始化器开始工作 // 遍历调用SpringApplicationRunListener的contextPrepared方法。目前只是将这个事件广播器注册到Spring容器中 listeners.contextPrepared(context); if (this.logStartupInfo) { logStartupInfo(context.getParent() == null); logStartupProfileInfo(context); }
 // 把应用程序参数持有类注册到Spring容器中，并且是一个单例 context.getBeanFactory().registerSingleton("springApplicationArguments", applicationArguments);
 Set<Object> sources = getSources(); Assert.notEmpty(sources, "Sources must not be empty"); load(context, sources.toArray(new Object[sources.size()])); // 广播出ApplicationPreparedEvent事件给相应的监听器执行 listeners.contextLoaded(context);
 // Spring容器的刷新 refresh(context); if (this.registerShutdownHook) { try { context.registerShutdownHook(); } catch (AccessControlException ex) { // Not allowed in some environments. } } return context;}

protected ConfigurableApplicationContext createApplicationContext() { Class<?> contextClass = this.applicationContextClass; if (contextClass == null) { try { // 如果是web程序，那么构造org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext容器 // 否则构造org.springframework.context.annotation.AnnotationConfigApplicationContext容器 contextClass = Class.forName(this.webEnvironment ? DEFAULT_WEB_CONTEXT_CLASS : DEFAULT_CONTEXT_CLASS); } catch (ClassNotFoundException ex) { throw new IllegalStateException( "Unable create a default ApplicationContext, " + "please specify an ApplicationContextClass", ex); } } return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);}

 protected void postProcessApplicationContext(ConfigurableApplicationContext context) { if (this.webEnvironment) { // 如果是web程序 if (context instanceof ConfigurableWebApplicationContext) { // 并且也是Spring Web容器 ConfigurableWebApplicationContext configurableContext = (ConfigurableWebApplicationContext) context; if (this.beanNameGenerator != null) { // 如果SpringApplication设置了是实例命名生成器，注册到Spring容器中 configurableContext.getBeanFactory().registerSingleton( AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR, this.beanNameGenerator); } } } if (this.resourceLoader != null) { // 如果SpringApplication设置了资源加载器，设置到Spring容器中 if (context instanceof GenericApplicationContext) { ((GenericApplicationContext) context) .setResourceLoader(this.resourceLoader); } if (context instanceof DefaultResourceLoader) { ((DefaultResourceLoader) context) .setClassLoader(this.resourceLoader.getClassLoader()); } }}

protected void applyInitializers(ConfigurableApplicationContext context) { // 遍历每个初始化器，对调用对应的initialize方法 for (ApplicationContextInitializer initializer : getInitializers()) { Class<?> requiredType = GenericTypeResolver.resolveTypeArgument( initializer.getClass(), ApplicationContextInitializer.class); Assert.isInstanceOf(requiredType, context, "Unable to call initializer."); initializer.initialize(context); }}

 protected void afterRefresh(ConfigurableApplicationContext context, ApplicationArguments args) { afterRefresh(context, args.getSourceArgs()); // 目前是个空实现 callRunners(context, args); // 调用Spring容器中的ApplicationRunner和CommandLineRunner接口的实现类 }
 private void callRunners(ApplicationContext context, ApplicationArguments args) { List<Object> runners = new ArrayList<Object>(); // 找出Spring容器中ApplicationRunner接口的实现类 runners.addAll(context.getBeansOfType(ApplicationRunner.class).values()); // 找出Spring容器中CommandLineRunner接口的实现类 runners.addAll(context.getBeansOfType(CommandLineRunner.class).values()); // 对runners进行排序 AnnotationAwareOrderComparator.sort(runners); // 遍历runners依次执行 for (Object runner : new LinkedHashSet<Object>(runners)) { if (runner instanceof ApplicationRunner) { // 如果是ApplicationRunner，进行ApplicationRunner的run方法调用 callRunner((ApplicationRunner) runner, args); } if (runner instanceof CommandLineRunner) { // 如果是CommandLineRunner，进行CommandLineRunner的run方法调用 callRunner((CommandLineRunner) runner, args); } }}