【SpringBoot】启动流程之tomcat启动流程

SpringBoot启动流程之tomcat启动流程

我们先上图

我们下面附上源码
1.同样我们还是从SpringApplication.run(WebApplicaiton.class,args);这个入口进入。

public ConfigurableApplicationContext run(String... args) {
   long startTime = System.nanoTime();
   DefaultBootstrapContext bootstrapContext = createBootstrapContext();
   ConfigurableApplicationContext context = null;
   configureHeadlessProperty();
   SpringApplicationRunListeners listeners = getRunListeners(args);
   listeners.starting(bootstrapContext, this.mainApplicationClass);
   try {
      ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
      ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
      configureIgnoreBeanInfo(environment);
      Banner printedBanner = printBanner(environment);
      context = createApplicationContext();
      context.setApplicationStartup(this.applicationStartup);
      prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
      refreshContext(context);
      afterRefresh(context, applicationArguments);
      Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);
      if (this.logStartupInfo) {
         new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);
      }
      listeners.started(context, timeTakenToStartup);
      callRunners(context, applicationArguments);
   }
   catch (Throwable ex) {
      handleRunFailure(context, ex, listeners);
      throw new IllegalStateException(ex);
   }
   try {
      Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);
      listeners.ready(context, timeTakenToReady);
   }
   catch (Throwable ex) {
      handleRunFailure(context, ex, null);
      throw new IllegalStateException(ex);
   }
   return context;
}

2.找到refreshContext方法并进入

private void refreshContext(ConfigurableApplicationContext context) {
   if (this.registerShutdownHook) {
      shutdownHook.registerApplicationContext(context);
   }
   refresh(context);
}

3.找到refresh方法并进入

protected void refresh(ConfigurableApplicationContext applicationContext) {
   applicationContext.refresh();
}

4.进入到AbstractApplicationContext下的refresh()

@Override
public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

      // Prepare this context for refreshing.
      prepareRefresh();

      // Tell the subclass to refresh the internal bean factory.
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      // Prepare the bean factory for use in this context.
      prepareBeanFactory(beanFactory);

      try {
         // Allows post-processing of the bean factory in context subclasses.
         postProcessBeanFactory(beanFactory);

         StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
         // Invoke factory processors registered as beans in the context.
         invokeBeanFactoryPostProcessors(beanFactory);

         // Register bean processors that intercept bean creation.
         registerBeanPostProcessors(beanFactory);
         beanPostProcess.end();

         // Initialize message source for this context.
         initMessageSource();

         // Initialize event multicaster for this context.
         initApplicationEventMulticaster();

         // Initialize other special beans in specific context subclasses.
         onRefresh();

         // Check for listener beans and register them.
         registerListeners();

         // Instantiate all remaining (non-lazy-init) singletons.
         finishBeanFactoryInitialization(beanFactory);

         // Last step: publish corresponding event.
         finishRefresh();
      }

      catch (BeansException ex) {
         if (logger.isWarnEnabled()) {
            logger.warn("Exception encountered during context initialization - " +
                  "cancelling refresh attempt: " + ex);
         }

         // Destroy already created singletons to avoid dangling resources.
         destroyBeans();

         // Reset 'active' flag.
         cancelRefresh(ex);

         // Propagate exception to caller.
         throw ex;
      }

      finally {
         // Reset common introspection caches in Spring's core, since we
         // might not ever need metadata for singleton beans anymore...
         resetCommonCaches();
         contextRefresh.end();
      }
   }
}

5.我们会看到一个钩子方法，用于给子类进行扩展的方法

//钩子方法
protected void onRefresh() throws BeansException {
}

6.我们进入ServletWebServerApplicationContext下的onRefresh方法

@Override
protected void onRefresh() {
   super.onRefresh();
   try {
       //创建webserver容器
      createWebServer();
   }
   catch (Throwable ex) {
      throw new ApplicationContextException("Unable to start web server", ex);
   }
}

7.进入createWebServer方法

private void createWebServer() {
   WebServer webServer = this.webServer;
   ServletContext servletContext = getServletContext();
   if (webServer == null && servletContext == null) {
      StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");
      //工厂模式 得到一个创建服务的工厂
      ServletWebServerFactory factory = getWebServerFactory();
      createWebServer.tag("factory", factory.getClass().toString());
      //创建一个服务器我们这里举例tomcat 看下方详情代码
      this.webServer = factory.getWebServer(getSelfInitializer());
      createWebServer.end();
      getBeanFactory().registerSingleton("webServerGracefulShutdown",
            new WebServerGracefulShutdownLifecycle(this.webServer));
      getBeanFactory().registerSingleton("webServerStartStop",
            new WebServerStartStopLifecycle(this, this.webServer));
   }
   else if (servletContext != null) {
      try {
         getSelfInitializer().onStartup(servletContext);
      }
      catch (ServletException ex) {
         throw new ApplicationContextException("Cannot initialize servlet context", ex);
      }
   }
   initPropertySources();
}

8.再进入getWebServer方法

@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
   if (this.disableMBeanRegistry) {
      Registry.disableRegistry();
   }
   Tomcat tomcat = new Tomcat();
   File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
   tomcat.setBaseDir(baseDir.getAbsolutePath());
   for (LifecycleListener listener : this.serverLifecycleListeners) {
      tomcat.getServer().addLifecycleListener(listener);
   }
   Connector connector = new Connector(this.protocol);
   connector.setThrowOnFailure(true);
   tomcat.getService().addConnector(connector);
   customizeConnector(connector);
   tomcat.setConnector(connector);
   tomcat.getHost().setAutoDeploy(false);
   configureEngine(tomcat.getEngine());
   for (Connector additionalConnector : this.additionalTomcatConnectors) {
      tomcat.getService().addConnector(additionalConnector);
   }
   prepareContext(tomcat.getHost(), initializers);
   //得到web的服务端
   return getTomcatWebServer(tomcat);
}

9.得到web的服务端

protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
   return new TomcatWebServer(tomcat, getPort() >= 0, getShutdown());
}

public TomcatWebServer(Tomcat tomcat, boolean autoStart, Shutdown shutdown) {
   Assert.notNull(tomcat, "Tomcat Server must not be null");
   this.tomcat = tomcat;
   this.autoStart = autoStart;
   this.gracefulShutdown = (shutdown == Shutdown.GRACEFUL) ? new GracefulShutdown(tomcat) : null;
   initialize();
}

11.初始化操作

private void initialize() throws WebServerException {
   logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
   synchronized (this.monitor) {
      try {
         addInstanceIdToEngineName();

         Context context = findContext();
         context.addLifecycleListener((event) -> {
            if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {
               // Remove service connectors so that protocol binding doesn't
               // happen when the service is started.
               removeServiceConnectors();
            }
         });

         // Start the server to trigger initialization listeners
         //启动tomcat
         this.tomcat.start();

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

         try {
            ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
         }
         catch (NamingException ex) {
            // Naming is not enabled. Continue
         }

         // Unlike Jetty, all Tomcat threads are daemon threads. We create a
         // blocking non-daemon to stop immediate shutdown
         //创建一个阻塞的非守护进程来停止立即关闭
         startDaemonAwaitThread();
      }
      catch (Exception ex) {
         stopSilently();
         destroySilently();
         throw new WebServerException("Unable to start embedded Tomcat", ex);
      }
   }
}

12.启动tomcat

private void startDaemonAwaitThread() {
   Thread awaitThread = new Thread("container-" + (containerCounter.get())) {

      @Override
      public void run() {
         TomcatWebServer.this.tomcat.getServer().await();
      }

   };
   awaitThread.setContextClassLoader(getClass().getClassLoader());
   awaitThread.setDaemon(false);
   awaitThread.start();
}