SpringBoot中如何启动Tomcat流程

// Create, load, refresh and run the ApplicationContext
context = createApplicationContext();

protected ConfigurableApplicationContext createApplicationContext() {
  Class<?> contextClass = this.applicationContextClass;
  if (contextClass == null) {
    try {
     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);
}
 

AnnotationConfigEmbeddedWebApplicationContext

@Override
 protected void onRefresh() {
  super.onRefresh();
  try {
    createEmbeddedServletContainer();
  }
  catch (Throwable ex) {
    throw new ApplicationContextException("Unable to start embedded container",
       ex);
  }
}

private void createEmbeddedServletContainer() {
  EmbeddedServletContainer localContainer = this.embeddedServletContainer;
  ServletContext localServletContext = getServletContext();
  if (localContainer == null && localServletContext == null) {
    EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
    this.embeddedServletContainer = containerFactory
       .getEmbeddedServletContainer(getSelfInitializer());
  }
  else if (localServletContext != null) {
   try {
     getSelfInitializer().onStartup(localServletContext);
   }
   catch (ServletException ex) {
     throw new ApplicationContextException("Cannot initialize servlet context",
        ex);
   }
  }
  initPropertySources();
}

public interface EmbeddedServletContainerFactory {
 
  /**
   * 创建一个配置完全的但是目前还处于“pause”状态的实例.
   * 只有其 start 方法被调用后，Client 才能与其建立连接。
   */
  EmbeddedServletContainer getEmbeddedServletContainer(
     ServletContextInitializer... initializers);
 
}

 @Override
 public EmbeddedServletContainer getEmbeddedServletContainer(
    ServletContextInitializer... initializers) {
  Tomcat tomcat = new Tomcat();
  File baseDir = (this.baseDirectory != null ? this.baseDirectory
     : createTempDir("tomcat"));
  tomcat.setBaseDir(baseDir.getAbsolutePath());
  Connector connector = new Connector(this.protocol);
  tomcat.getService().addConnector(connector);
  customizeConnector(connector);
  tomcat.setConnector(connector);
  tomcat.getHost().setAutoDeploy(false);
  tomcat.getEngine().setBackgroundProcessorDelay(-);
  for (Connector additionalConnector : this.additionalTomcatConnectors) {
   tomcat.getService().addConnector(additionalConnector);
  }
  prepareContext(tomcat.getHost(), initializers);
  return getTomcatEmbeddedServletContainer(tomcat);
}

 if (isRegisterDefaultServlet()) {
  addDefaultServlet(context);
 }
 if (isRegisterJspServlet() && ClassUtils.isPresent(getJspServletClassName(),
    getClass().getClassLoader())) {
  addJspServlet(context);
  addJasperInitializer(context);
  context.addLifecycleListener(new StoreMergedWebXmlListener());
 }
ServletContextInitializer[] initializersToUse = mergeInitializers(initializers);
configureContext(context, initializersToUse);

private synchronized void initialize() throws EmbeddedServletContainerException {
  TomcatEmbeddedServletContainer.logger
     .info("Tomcat initialized with port(s): " + getPortsDescription(false));
  try {
    addInstanceIdToEngineName();
 
    // Remove service connectors to that protocol binding doesn't happen yet
    removeServiceConnectors();
 
   // Start the server to trigger initialization listeners
   this.tomcat.start();

   // We can re-throw failure exception directly in the main thread
   rethrowDeferredStartupExceptions();

   // Unlike Jetty, all Tomcat threads are daemon threads. We create a
   // blocking non-daemon to stop immediate shutdown
   startDaemonAwaitThread();
  }
  catch (Exception ex) {
   throw new EmbeddedServletContainerException("Unable to start embedded Tomcat",
      ex);
  }
}

private ServletContextInitializer getSelfInitializer() {
  return new ServletContextInitializer() {
   @Override
   public void onStartup(ServletContext servletContext) throws ServletException {
     selfInitialize(servletContext);
   }
  };
}

private void selfInitialize(ServletContext servletContext) throws ServletException {
  prepareEmbeddedWebApplicationContext(servletContext);
  ConfigurableListableBeanFactory beanFactory = getBeanFactory();
  ExistingWebApplicationScopes existingScopes = new ExistingWebApplicationScopes(
     beanFactory);
  WebApplicationContextUtils.registerWebApplicationScopes(beanFactory,
     getServletContext());
  existingScopes.restore();
  WebApplicationContextUtils.registerEnvironmentBeans(beanFactory,
     getServletContext());
  for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
   beans.onStartup(servletContext);
  }
}

@Override
 public void onStartup(ServletContext servletContext) throws ServletException {
  Assert.notNull(this.servlet, "Servlet must not be null");
  String name = getServletName();
  if (!isEnabled()) {
    logger.info("Servlet " + name + " was not registered (disabled)");
    return;
  }
  logger.info("Mapping servlet: '" + name + "' to " + this.urlMappings);
  Dynamic added = servletContext.addServlet(name, this.servlet);
  if (added == null) {
   logger.info("Servlet " + name + " was not registered "
      + "(possibly already registered?)");
   return;
  }
  configure(added);
}