Spring Boot启动原理

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

1. new 一个SpringApplication 对象,进行初始化

   public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
       this.sources = new LinkedHashSet();
       this.bannerMode = Mode.CONSOLE;
       this.logStartupInfo = true;
       this.addCommandLineProperties = true;
       this.addConversionService = true;
       this.headless = true;
       this.registerShutdownHook = true;
       this.additionalProfiles = new HashSet();
       this.isCustomEnvironment = false;
       this.lazyInitialization = false;
       this.resourceLoader = resourceLoader;
       Assert.notNull(primarySources, "PrimarySources must not be null");
       this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
       this.webApplicationType = WebApplicationType.deduceFromClasspath();
       this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
       this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
       this.mainApplicationClass = this.deduceMainApplicationClass();
   }

• 推断WebApplicationType，主要思想就是在当前的classpath下搜索特定的类

• 搜索META-INF\spring.factories文件配置的ApplicationContextInitializer的实现类

• 搜索META-INF\spring.factories文件配置的ApplicationListenerr的实现类

• 推断MainApplication的Class

2. 运行run方法

1. 创建一个StopWatch并执行start方法，这个类主要记录任务的执行时间
2. 配置Headless属性，Headless模式是在缺少显示屏、键盘或者鼠标时候的系统配置
3. 在文件META-INF\spring.factories中获取SpringApplicationRunListener接口的实现类EventPublishingRunListener，主要发布SpringApplicationEvent
4. 把输入参数转成DefaultApplicationArguments类
5. 创建Environment并设置比如环境信息，系统熟悉，输入参数和profile信息
6. 打印Banner信息
7. 创建Application的上下文，根据WebApplicationTyp来创建Context类，如果非web项目则创建AnnotationConfigApplicationContext，在构造方法中初始化AnnotatedBeanDefinitionReader和ClassPathBeanDefinitionScanner
8. 在文件META-INF\spring.factories中获取SpringBootExceptionReporter接口的实现类FailureAnalyzers
9. 准备application的上下文
   9.1 初始化ApplicationContextInitializer
   9.2 执行Initializer的contextPrepared方法，发布ApplicationContextInitializedEvent事件
   9.3 如果延迟加载，在上下文添加处理器LazyInitializationBeanFactoryPostProcessor
   9.4 执行加载方法，BeanDefinitionLoader.load方法，主要初始化了AnnotatedGenericBeanDefinition
   9.5 执行Initializer的contextLoaded方法，发布ApplicationContextInitializedEvent事件
10. 刷新上下文（后文会单独分析refresh方法），在这里真正加载bean到容器中。如果是web容器，会在onRefresh方法中创建一个Server并启动。

  public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
        this.configureHeadlessProperty();
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        listeners.starting();

        Collection exceptionReporters;
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            Banner printedBanner = this.printBanner(environment);
            context = this.createApplicationContext();
            exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
            this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            this.refreshContext(context);
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }

            listeners.started(context);
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            this.handleRunFailure(context, var10, exceptionReporters, listeners);
            throw new IllegalStateException(var10);
        }

        try {
            listeners.running(context);
            return context;
        } catch (Throwable var9) {
            this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(var9);
        }
    }