SpringBoot启动流程

　　SpringBoot启动流程我们简单的先介绍一下SpringBoot的启动流程都需要哪些步骤 	1.加载配置文件 	2.准备上下文环境 	3.创建上下文对象 	4.启动spring 	5.启动tomcat
　　我们先来看一下springboot的启动流程图
　　SpringBoot启动流程图
　　下面附上源码，我们从 SpringApplication.run(WebApplicaiton.class,args); 开始进入
　　找到SpringApplication下的run方法。在代码中都有注释标注，相信大家都可以看懂 public ConfigurableApplicationContext run(String... args) {    long startTime = System.nanoTime();    DefaultBootstrapContext bootstrapContext = createBootstrapContext();    ConfigurableApplicationContext context = null;    //设置了一个名为java.awt.headless的系统属性    configureHeadlessProperty();    //获取监听器 所有实现SpringApplicationRunListener这个接口的监听器    SpringApplicationRunListeners listeners = getRunListeners(args);    //调用监听器里所有写的starting方法    listeners.starting(bootstrapContext, this.mainApplicationClass);    try {       ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);       //准备上下文的环境       ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);       configureIgnoreBeanInfo(environment);       //启动的图标       Banner printedBanner = printBanner(environment);       //创建上下文的对象       context = createApplicationContext();       context.setApplicationStartup(this.applicationStartup);       prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);       //进入到spring的容器方法       refreshContext(context);       afterRefresh(context, applicationArguments);       Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);       if (this.logStartupInfo) {          new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);       }       //调用了监听器的started方法       listeners.started(context, timeTakenToStartup);       callRunners(context, applicationArguments);    }    catch (Throwable ex) {       handleRunFailure(context, ex, listeners);       throw new IllegalStateException(ex);    }    try {        //计算springboot启动耗时       Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);       //执行监听器的ready方法       listeners.ready(context, timeTakenToReady);    }    catch (Throwable ex) {       handleRunFailure(context, ex, null);       throw new IllegalStateException(ex);    }    return context; }
　　我们再走到prepareContext方法中 private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context,       ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,       ApplicationArguments applicationArguments, Banner printedBanner) {    context.setEnvironment(environment);    postProcessApplicationContext(context);    applyInitializers(context);    //设置完环境变量 监听器会调用的方法    listeners.contextPrepared(context);    bootstrapContext.close(context);    if (this.logStartupInfo) {       logStartupInfo(context.getParent() == null);       logStartupProfileInfo(context);    }    // Add boot specific singleton beans    ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();    beanFactory.registerSingleton(＂springApplicationArguments＂, applicationArguments);    if (printedBanner != null) {       beanFactory.registerSingleton(＂springBootBanner＂, printedBanner);    }    if (beanFactory instanceof AbstractAutowireCapableBeanFactory) {       ((AbstractAutowireCapableBeanFactory) beanFactory).setAllowCircularReferences(this.allowCircularReferences);       if (beanFactory instanceof DefaultListableBeanFactory) {          ((DefaultListableBeanFactory) beanFactory)                .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);       }    }    if (this.lazyInitialization) {       context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());    }    // Load the sources    Set