springboot内置Tomcat流程

1、org.springframework.boot.SpringApplication#initialize

setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));

加载了org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext

2、spring refresh 中onRefresh回调中启动了内置Tomcat

ServletWebServerApplicationContext继承AbstractApplicationContext，并且重新实现了onRefresh方法。

	//重写了refresh方法，启动@Overrideprotected void onRefresh() {super.onRefresh();try {createWebServer();}catch (Throwable ex) {throw new ApplicationContextException("Unable to start web server", ex);}}//启动Tomcatprivate void createWebServer() {WebServer webServer = this.webServer;ServletContext servletContext = getServletContext();if (webServer == null && servletContext == null) {ServletWebServerFactory factory = getWebServerFactory();this.webServer = factory.getWebServer(getSelfInitializer());}else if (servletContext != null) {try {getSelfInitializer().onStartup(servletContext);}catch (ServletException ex) {throw new ApplicationContextException("Cannot initialize servlet context", ex);}}initPropertySources();}//如果Tomcat启动了，就发布服务ServletWebServerInitializedEvent@Overrideprotected void finishRefresh() {super.finishRefresh();WebServer webServer = startWebServer();if (webServer != null) {publishEvent(new ServletWebServerInitializedEvent(webServer, this));}}