jar包：执行SpringBoot主类的main方法，启动ioc容器，创建嵌入式的Servlet容器； war包：启动服务器，**服务器启动SpringBoot应用**【SpringBootServletInitializer】，启动ioc容器； servlet3.0（Spring注解版）： 8.2.4 Shared libraries / runtimes pluggability： 规则： ​ 1）、服务器启动（web应用启动）会创建当前web应用里面每一个jar包里面ServletContainerInitializer实例： ​ 2）、ServletContainerInitializer的实现放在jar包的META-INF/services文件夹下，有一个名为javax.servlet.ServletContainerInitializer的文件，内容就是ServletContainerInitializer的实现类的全类名 ​ 3）、还可以使用@HandlesTypes，在应用启动的时候加载我们感兴趣的类； 流程： 1）、启动Tomcat 2）、org\springframework\spring-web\4.3.14.RELEASE\spring-web-4.3.14.RELEASE.jar!\META-INF\services\javax.servlet.ServletContainerInitializer： Spring的web模块里面有这个文件：**org.springframework.web.SpringServletContainerInitializer** 3）、SpringServletContainerInitializer将@HandlesTypes(WebApplicationInitializer.class)标注的所有这个类型的类都传入到onStartup方法的Set<Class<?>>；为这些WebApplicationInitializer类型的类创建实例； 4）、每一个WebApplicationInitializer都调用自己的onStartup；  5）、相当于我们的SpringBootServletInitializer的类会被创建对象，并执行onStartup方法 6）、SpringBootServletInitializer实例执行onStartup的时候会createRootApplicationContext；创建容器 ```java protected WebApplicationContext createRootApplicationContext( ServletContext servletContext) { //1、创建SpringApplicationBuilder SpringApplicationBuilder builder = createSpringApplicationBuilder(); StandardServletEnvironment environment = new StandardServletEnvironment(); environment.initPropertySources(servletContext, null); builder.environment(environment); builder.main(getClass()); ApplicationContext parent = getExistingRootWebApplicationContext(servletContext); if (parent != null) { this.logger.info("Root context already created (using as parent)."); servletContext.setAttribute( WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, null); builder.initializers(new ParentContextApplicationContextInitializer(parent)); } builder.initializers( new ServletContextApplicationContextInitializer(servletContext)); builder.contextClass(AnnotationConfigEmbeddedWebApplicationContext.class); //调用configure方法，子类重写了这个方法，将SpringBoot的主程序类传入了进来 builder = configure(builder); //使用builder创建一个Spring应用 SpringApplication application = builder.build(); if (application.getSources().isEmpty() && AnnotationUtils .findAnnotation(getClass(), Configuration.class) != null) { application.getSources().add(getClass()); } Assert.state(!application.getSources().isEmpty(), "No SpringApplication sources have been defined. Either override the " + "configure method or add an @Configuration annotation"); // Ensure error pages are registered if (this.registerErrorPageFilter) { application.getSources().add(ErrorPageFilterConfiguration.class); } //启动Spring应用 return run(application); } ``` 7）、Spring的应用就启动并且创建IOC容器 ```java public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; FailureAnalyzers analyzers = null; configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); Banner printedBanner = printBanner(environment); context = createApplicationContext(); analyzers = new FailureAnalyzers(context); prepareContext(context, environment, listeners, applicationArguments, printedBanner); //刷新IOC容器 refreshContext(context); afterRefresh(context, applicationArguments); listeners.finished(context, null); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } return context; } catch (Throwable ex) { handleRunFailure(context, listeners, analyzers, ex); throw new IllegalStateException(ex); } } ``` **==启动Servlet容器，再启动SpringBoot应用==**