玩转 Spring Boot 原理篇（内嵌Tomcat实现原理&优雅停机源码剖析）

@Configuration(proxyBeanMethods = false)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
      ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
      ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
      ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {
     // ... ...
}
 
public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
    // ... ...
}

@Override
protected void onRefresh() {
   super.onRefresh();
   try {
      logger.info("【ServletWebServerApplicationContext】【onRefresh】-【开始创建 WEB 服务】");
      // 开始创建 WEB 服务
      createWebServer();
      logger.info("【ServletWebServerApplicationContext】【onRefresh】-【方法执行完毕，创建 WEB 服务完成】");
   }
   catch (Throwable ex) {
      throw new ApplicationContextException("Unable to start web server", ex);
   }
}

// 创建 WEB 服务
 private void createWebServer() {
  WebServer webServer = this.webServer;
  ServletContext servletContext = getServletContext();
  if (webServer == null && servletContext == null) {
   ServletWebServerFactory factory = getWebServerFactory();
   // 重点在这里，主要看这个方法的内部
   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();
 }

// Tomcat 对象的初始化
@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
   if (this.disableMBeanRegistry) {
      Registry.disableRegistry();
   }
   // 完成 Tomcat 的 API 调用
   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);
   }
   // 准备 TomcatEmbeddedContext 并设置到 Tomcat 中
   prepareContext(tomcat.getHost(), initializers);
   // 构建 TomcatWebServer
   return getTomcatWebServer(tomcat);
}

// 获取 Tomcat 服务
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;
   // 调用  TomcatWebServer#initialize 方法
   initialize();
}

// 完成 Tomcat 的初始化
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
         //启动服务触发初始化监听器
         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
         // Tomcat 的线程都是守护线程，我们创建一个阻塞非守护线程来避免立即关闭
         startDaemonAwaitThread();
      }
      catch (Exception ex) {
         stopSilently();
         destroySilently();
         throw new WebServerException("Unable to start embedded Tomcat", ex);
      }
   }
}

protected void finishRefresh() {
   // Clear context-level resource caches (such as ASM metadata from scanning).
   clearResourceCaches();
 
   // Initialize lifecycle processor for this context.
   // 为此上下文初始化 lifecycle processor。
   initLifecycleProcessor();
 
   // Propagate refresh to lifecycle processor first.
   getLifecycleProcessor().onRefresh();
 
   // Publish the final event.
   publishEvent(new ContextRefreshedEvent(this));
 
   // Participate in LiveBeansView MBean, if active.
   if (!NativeDetector.inNativeImage()) {
      LiveBeansView.registerApplicationContext(this);
   }
}

@Override
public void onRefresh() {
   startBeans(true);
   this.running = true;
}

## 开启优雅停机, 如果不配置是默认IMMEDIATE, 立即停机
server.shutdown=graceful
## 优雅停机宽限期时间
spring.lifecycle.timeout-per-shutdown-phase=20s

TomcatWebServer stop() ----
INFO 60456 --- [ionShutdownHook] s.tomcat.SampleTomcatApplication         : ServletContext destroyed
Disconnected from the target VM, address: '127.0.0.1:50735', transport: 'socket'
Process finished with exit code 130 (interrupted by signal 2: SIGINT)