ServletWebServerApplicationContext创建Web容器Tomcat示例

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

private void createWebServer() {
   WebServer webServer = this.webServer;
   ServletContext servletContext = getServletContext();
   if (webServer == null && servletContext == null) {
      //一、获取Web服务器工厂
      ServletWebServerFactory factory = getWebServerFactory();
      //二、获取Web服务
      this.webServer = factory.getWebServer(getSelfInitializer());
      //三、注册Bean生命周期（在容器启动和销毁时调用）
      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);
      }
   }
   //四、初始化上下文环境
   initPropertySources();
}

protected ServletWebServerFactory getWebServerFactory() {
   // Use bean names so that we don't consider the hierarchy
   //获取Web服务器工厂名称
   String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);
   if (beanNames.length == 0) {
      throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing "
            + "ServletWebServerFactory bean.");
   }
   if (beanNames.length > 1) {
      throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "
            + "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
   }
   //从容器中获取Web服务器工厂实例
   return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}

@Configuration(proxyBeanMethods = false)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
//Web启动环境
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
//2.1导入Web工厂
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
      ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
      ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
      ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {
   //导入Web服务器工厂自定义程序
   @Bean
   public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(ServerProperties serverProperties) {
      return new ServletWebServerFactoryCustomizer(serverProperties);
   }
   //如果是Tomcat则导入Tomcat自定义程序
   @Bean
   @ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
   public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
         ServerProperties serverProperties) {
      return new TomcatServletWebServerFactoryCustomizer(serverProperties);
   }
   @Bean
   @ConditionalOnMissingFilterBean(ForwardedHeaderFilter.class)
   @ConditionalOnProperty(value = "server.forward-headers-strategy", havingValue = "framework")
   public FilterRegistrationBean<ForwardedHeaderFilter> forwardedHeaderFilter() {
      ForwardedHeaderFilter filter = new ForwardedHeaderFilter();
      FilterRegistrationBean<ForwardedHeaderFilter> registration = new FilterRegistrationBean<>(filter);
      registration.setDispatcherTypes(DispatcherType.REQUEST, DispatcherType.ASYNC, DispatcherType.ERROR);
      registration.setOrder(Ordered.HIGHEST_PRECEDENCE);
      return registration;
   }
   /**
    * Registers a {@link WebServerFactoryCustomizerBeanPostProcessor}. Registered via
    * {@link ImportBeanDefinitionRegistrar} for early registration.
    */
   public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
      private ConfigurableListableBeanFactory beanFactory;
      @Override
      public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
         if (beanFactory instanceof ConfigurableListableBeanFactory) {
            this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
         }
      }
      @Override
      public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
            BeanDefinitionRegistry registry) {
         if (this.beanFactory == null) {
            return;
         }
         registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor",
               WebServerFactoryCustomizerBeanPostProcessor.class);
         registerSyntheticBeanIfMissing(registry, "errorPageRegistrarBeanPostProcessor",
               ErrorPageRegistrarBeanPostProcessor.class);
      }
      private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name, Class<?> beanClass) {
         if (ObjectUtils.isEmpty(this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
            RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
            beanDefinition.setSynthetic(true);
            registry.registerBeanDefinition(name, beanDefinition);
         }
      }
   }
}

@Configuration
class ServletWebServerFactoryConfiguration {
    ServletWebServerFactoryConfiguration() {
    }
    //1.如果容器中有Servlet，Undertow，SslClientAuthMode就会创建Undertow工厂
    @Configuration
    @ConditionalOnClass({Servlet.class, Undertow.class, SslClientAuthMode.class})
    @ConditionalOnMissingBean(
        value = {ServletWebServerFactory.class},
        search = SearchStrategy.CURRENT
    )
    public static class EmbeddedUndertow {
        public EmbeddedUndertow() {
        }
        @Bean
        public UndertowServletWebServerFactory undertowServletWebServerFactory() {
            return new UndertowServletWebServerFactory();
        }
    }
    //2.如果容器中有Servlet，Server，Loader就会创建Jetty工厂
    @Configuration
    @ConditionalOnClass({Servlet.class, Server.class, Loader.class, WebAppContext.class})
    @ConditionalOnMissingBean(
        value = {ServletWebServerFactory.class},
        search = SearchStrategy.CURRENT
    )
    public static class EmbeddedJetty {
        public EmbeddedJetty() {
        }
        @Bean
        public JettyServletWebServerFactory JettyServletWebServerFactory() {
            return new JettyServletWebServerFactory();
        }
    }
    //3.如果容器中有Servlet，Tomcat，UpgradeProtocol就会创建Tomcat工厂
    @Configuration
    @ConditionalOnClass({Servlet.class, Tomcat.class, UpgradeProtocol.class})
    @ConditionalOnMissingBean(
        value = {ServletWebServerFactory.class},
        search = SearchStrategy.CURRENT
    )
    public static class EmbeddedTomcat {
        public EmbeddedTomcat() {
        }
        @Bean
        public TomcatServletWebServerFactory tomcatServletWebServerFactory() {
            return new TomcatServletWebServerFactory();
        }
    }
}

public static final String DEFAULT_PROTOCOL = "org.apache.coyote.http11.Http11NioProtocol";
private String protocol = DEFAULT_PROTOCOL;
public WebServer getWebServer(ServletContextInitializer... initializers) {
    Tomcat tomcat = new Tomcat();
    // 给嵌入式Tomcat创建一个临时文件夹，用于存放Tomcat运行中需要的文件
    File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
    tomcat.setBaseDir(baseDir.getAbsolutePath());
    // Tomcat核心概念：Connector，默认放入的protocol为NIO模式
    Connector connector = new Connector(this.protocol);
    // 给Service添加Connector
    tomcat.getService().addConnector(connector);
    // 执行定制器，修改即将设置到Tomcat中的Connector
    customizeConnector(connector);
    tomcat.setConnector(connector);
    // 关闭热部署（嵌入式Tomcat不存在修改web.xml、war包等情况）
    tomcat.getHost().setAutoDeploy(false);
    // 设置backgroundProcessorDelay机制
    configureEngine(tomcat.getEngine());
    for (Connector additionalConnector : this.additionalTomcatConnectors) {
        tomcat.getService().addConnector(additionalConnector);
    }
    // 2.1 创建TomcatEmbeddedContext
    prepareContext(tomcat.getHost(), initializers);
    // 2.2. 创建TomcatWebServer
    return getTomcatWebServer(tomcat);
}

protected void prepareContext(Host host, ServletContextInitializer[] initializers) {
    File documentRoot = getValidDocumentRoot();
    // 创建TomcatEmbeddedContext
    TomcatEmbeddedContext context = new TomcatEmbeddedContext();
    if (documentRoot != null) {
        context.setResources(new LoaderHidingResourceRoot(context));
    }
    context.setName(getContextPath());
    context.setDisplayName(getDisplayName());
    // 设置contextPath，很熟悉了
    context.setPath(getContextPath());
    // 给嵌入式Tomcat创建docbase的临时文件夹
    File docBase = (documentRoot != null) ? documentRoot : createTempDir("tomcat-docbase");
    context.setDocBase(docBase.getAbsolutePath());
    // 注册监听器
    context.addLifecycleListener(new FixContextListener());
    context.setParentClassLoader((this.resourceLoader != null) ? this.resourceLoader.getClassLoader()
            : ClassUtils.getDefaultClassLoader());
    // 设置默认编码映射
    resetDefaultLocaleMapping(context);
    addLocaleMappings(context);
    context.setUseRelativeRedirects(false);
    try {
        context.setCreateUploadTargets(true);
    }
    catch (NoSuchMethodError ex) {
        // Tomcat is < 8.5.39. Continue.
    }
    configureTldSkipPatterns(context);
    // 自定义的类加载器，可以加载web应用的jar包
    WebappLoader loader = new WebappLoader(context.getParentClassLoader());
    loader.setLoaderClass(TomcatEmbeddedWebappClassLoader.class.getName());
    // 指定类加载器遵循双亲委派机制
    loader.setDelegate(true);
    context.setLoader(loader);
    // 注册默认的Servlet
    if (isRegisterDefaultServlet()) {
        addDefaultServlet(context);
    }
    // 如果需要jsp支持，注册jsp的Servlet和Initializer
    if (shouldRegisterJspServlet()) {
        addJspServlet(context);
        addJasperInitializer(context);
    }
    // 注册监听器
    context.addLifecycleListener(new StaticResourceConfigurer(context));
    ServletContextInitializer[] initializersToUse = mergeInitializers(initializers);
    host.addChild(context);
    configureContext(context, initializersToUse);
    postProcessContext(context);
}

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

public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
    Assert.notNull(tomcat, "Tomcat Server must not be null");
    this.tomcat = tomcat;
    this.autoStart = autoStart;
    //初始化服务
    initialize();
}

private void initialize() throws WebServerException {
   logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
   synchronized (this.monitor) {
      try {
         //设置Engine的id
         addInstanceIdToEngineName();
         //获取Context（TomcatEmbeddedContext  2.1中创建出来的）
         Context context = findContext();
         //添加监听器 TomcatEmbeddedContext
         //在服务启动时如果有连接进来先删除连接，以便在启动服务时不会发生协议绑定。
         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.
               //删除ServiceConnectors，以便在启动服务时不会发生协议绑定。
               removeServiceConnectors();
            }
         });
         // Start the server to trigger initialization listeners
         //2.2.1 启动Tomcat
         this.tomcat.start();
         // We can re-throw failure exception directly in the main thread
         //Tomcat启动有异常需要在主线程中抛出
         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
         //开启阻塞非守护线程停止web容器
         startDaemonAwaitThread();
      }
      catch (Exception ex) {
         stopSilently();
         destroySilently();
         throw new WebServerException("Unable to start embedded Tomcat", ex);
      }
   }
}

public void start() throws LifecycleException {
    //创建服务（Server和Service）
    getServer();
    server.start();
}

public final synchronized void start() throws LifecycleException {
    //如果是正在启动或启动状态
    if (LifecycleState.STARTING_PREP.equals(state) || LifecycleState.STARTING.equals(state) ||
            LifecycleState.STARTED.equals(state)) {
        if (log.isDebugEnabled()) {
            Exception e = new LifecycleException();
            log.debug(sm.getString("lifecycleBase.alreadyStarted", toString()), e);
        } else if (log.isInfoEnabled()) {
            log.info(sm.getString("lifecycleBase.alreadyStarted", toString()));
        }
        return;
    }
    //如果是新建状态
    if (state.equals(LifecycleState.NEW)) {
        //2.2.1.1 初始化服务
        init();
    //如果是失败状态    
    } else if (state.equals(LifecycleState.FAILED)) {
        //停止服务
        stop();
    //如果不是初始化也不是停止状态
    } else if (!state.equals(LifecycleState.INITIALIZED) &&
            !state.equals(LifecycleState.STOPPED)) {
        //修改状态
        invalidTransition(Lifecycle.BEFORE_START_EVENT);
    }
    try {
        //修改状态为准备启动
        setStateInternal(LifecycleState.STARTING_PREP, null, false);
        //2.2.1.2 启动Internal
        startInternal();
        if (state.equals(LifecycleState.FAILED)) {
            // This is a 'controlled' failure. The component put itself into the
            // FAILED state so call stop() to complete the clean-up.
            stop();
        } else if (!state.equals(LifecycleState.STARTING)) {
            // Shouldn't be necessary but acts as a check that sub-classes are
            // doing what they are supposed to.
            invalidTransition(Lifecycle.AFTER_START_EVENT);
        } else {
            setStateInternal(LifecycleState.STARTED, null, false);
        }
    } catch (Throwable t) {
        // This is an 'uncontrolled' failure so put the component into the
        // FAILED state and throw an exception.
        handleSubClassException(t, "lifecycleBase.startFail", toString());
    }
}

public final synchronized void init() throws LifecycleException {
    if (!state.equals(LifecycleState.NEW)) {
        invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
    }
    try {
        //设置状态为初始化
        setStateInternal(LifecycleState.INITIALIZING, null, false);
        //初始化
        initInternal();
        //设置状态为初始化完成
        setStateInternal(LifecycleState.INITIALIZED, null, false);
    } catch (Throwable t) {
        handleSubClassException(t, "lifecycleBase.initFail", toString());
    }
}

protected void initInternal() throws LifecycleException {
    //调用父类初始化（设置名称：Tomcat，类型：Server）
    super.initInternal();
    // Initialize utility executor
    reconfigureUtilityExecutor(getUtilityThreadsInternal(utilityThreads));
    //注册线程池
    register(utilityExecutor, "type=UtilityExecutor");
    // Register global String cache
    // Note although the cache is global, if there are multiple Servers
    // present in the JVM (may happen when embedding) then the same cache
    // will be registered under multiple names
    //注册字符串缓存
    onameStringCache = register(new StringCache(), "type=StringCache");
    // Register the MBeanFactory
    MBeanFactory factory = new MBeanFactory();
    factory.setContainer(this);
    //注册Bean工厂
    onameMBeanFactory = register(factory, "type=MBeanFactory");
    // Register the naming resources
    //注册命名资源
    globalNamingResources.init();
    // Populate the extension validator with JARs from common and shared
    // class loaders
    if (getCatalina() != null) {
        ClassLoader cl = getCatalina().getParentClassLoader();
        // Walk the class loader hierarchy. Stop at the system class loader.
        // This will add the shared (if present) and common class loaders
        while (cl != null && cl != ClassLoader.getSystemClassLoader()) {
            if (cl instanceof URLClassLoader) {
                URL[] urls = ((URLClassLoader) cl).getURLs();
                for (URL url : urls) {
                    if (url.getProtocol().equals("file")) {
                        try {
                            File f = new File (url.toURI());
                            if (f.isFile() &&
                                    f.getName().endsWith(".jar")) {
                                ExtensionValidator.addSystemResource(f);
                            }
                        } catch (URISyntaxException e) {
                            // Ignore
                        } catch (IOException e) {
                            // Ignore
                        }
                    }
                }
            }
            cl = cl.getParent();
        }
    }
    // Initialize our defined Services
    //2.2.1.1.1 初始化service（2.2.1最开始时创建）
    for (Service service : services) {
        service.init();
    }
}

public final synchronized void init() throws LifecycleException {
    if (!state.equals(LifecycleState.NEW)) {
        invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
    }
    try {
        //设置状态为初始化
        setStateInternal(LifecycleState.INITIALIZING, null, false);
        //初始化
        initInternal();
        //设置状态为初始化完成
        setStateInternal(LifecycleState.INITIALIZED, null, false);
    } catch (Throwable t) {
        handleSubClassException(t, "lifecycleBase.initFail", toString());
    }
}

protected void initInternal() throws LifecycleException {
    //调用父类初始化（设置名称：Tomcat，类型：Server）
    super.initInternal();
    //2.2.1.1.1.1 初始化engine
    if (engine != null) {
        engine.init();
    }
    // Initialize any Executors
    //2.2.1.1.1.2 初始化executor
    for (Executor executor : findExecutors()) {
        if (executor instanceof JmxEnabled) {
            ((JmxEnabled) executor).setDomain(getDomain());
        }
        executor.init();
    }
    // Initialize mapper listener
    //2.2.1.1.1.3 初始化mapperListener
    mapperListener.init();
    // Initialize our defined Connectors
    //2.2.1.1.1.4 初始化connector
    synchronized (connectorsLock) {
        for (Connector connector : connectors) {
            connector.init();
        }
    }
}

protected void initInternal() throws LifecycleException {
    // Ensure that a Realm is present before any attempt is made to start
    // one. This will create the default NullRealm if necessary.
    // 在尝试启动一个Realm之前，请确保存在一个Realm。如有必要，这将创建默认的NullRealm
    getRealm();
    super.initInternal();
}
public Realm getRealm() {
    Realm configured = super.getRealm();
    // If no set realm has been called - default to NullRealm
    // This can be overridden at engine, context and host level
    if (configured == null) {
        configured = new NullRealm();
        this.setRealm(configured);
    }
    return configured;
}

protected void initInternal() throws LifecycleException {
    super.initInternal();
}

protected void initInternal() throws LifecycleException {
    // If oname is not null then registration has already happened via preRegister().
    // 如果oname不为null，则已经通过preRegister()进行了注册
    if (oname == null) {
        mserver = Registry.getRegistry(null, null).getMBeanServer();
        oname = register(this, getObjectNameKeyProperties());
    }
}

protected void initInternal() throws LifecycleException {
    super.initInternal();
    if (protocolHandler == null) {
        throw new LifecycleException(
                sm.getString("coyoteConnector.protocolHandlerInstantiationFailed"));
    }
    // Initialize adapter
    adapter = new CoyoteAdapter(this);
    protocolHandler.setAdapter(adapter);
    if (service != null) {
        protocolHandler.setUtilityExecutor(service.getServer().getUtilityExecutor());
    }
    // Make sure parseBodyMethodsSet has a default
    if (null == parseBodyMethodsSet) {
        setParseBodyMethods(getParseBodyMethods());
    }
    if (protocolHandler.isAprRequired() && !AprStatus.isInstanceCreated()) {
        throw new LifecycleException(sm.getString("coyoteConnector.protocolHandlerNoAprListener",
                getProtocolHandlerClassName()));
    }
    if (protocolHandler.isAprRequired() && !AprStatus.isAprAvailable()) {
        throw new LifecycleException(sm.getString("coyoteConnector.protocolHandlerNoAprLibrary",
                getProtocolHandlerClassName()));
    }
    if (AprStatus.isAprAvailable() && AprStatus.getUseOpenSSL() &&
            protocolHandler instanceof AbstractHttp11JsseProtocol) {
        AbstractHttp11JsseProtocol<?> jsseProtocolHandler =
                (AbstractHttp11JsseProtocol<?>) protocolHandler;
        if (jsseProtocolHandler.isSSLEnabled() &&
                jsseProtocolHandler.getSslImplementationName() == null) {
            // OpenSSL is compatible with the JSSE configuration, so use it if APR is available
            jsseProtocolHandler.setSslImplementationName(OpenSSLImplementation.class.getName());
        }
    }
    try {
        //2.2.1.1.1.5 初始化protocolHandler
        protocolHandler.init();
    } catch (Exception e) {
        throw new LifecycleException(
                sm.getString("coyoteConnector.protocolHandlerInitializationFailed"), e);
    }
}

public void init() throws Exception {
    // Upgrade protocols have to be configured first since the endpoint
    // init (triggered via super.init() below) uses this list to configure
    // the list of ALPN protocols to advertise
    // 必须先配置升级协议，因为端点初始化（通过下面的super.init()触发）使用此列表来配置要发布的ALPN协议列表
    for (UpgradeProtocol upgradeProtocol : upgradeProtocols) {
        configureUpgradeProtocol(upgradeProtocol);
    }
    super.init();
}

public void init() throws Exception {
    if (getLog().isInfoEnabled()) {
        getLog().info(sm.getString("abstractProtocolHandler.init", getName()));
        logPortOffset();
    }
    if (oname == null) {
        // Component not pre-registered so register it
        oname = createObjectName();
        if (oname != null) {
            Registry.getRegistry(null, null).registerComponent(this, oname, null);
        }
    }
    if (this.domain != null) {
        rgOname = new ObjectName(domain + ":type=GlobalRequestProcessor,name=" + getName());
        Registry.getRegistry(null, null).registerComponent(
                getHandler().getGlobal(), rgOname, null);
    }
    String endpointName = getName();
    endpoint.setName(endpointName.substring(1, endpointName.length()-1));
    endpoint.setDomain(domain);
    //2.2.1.1.1.6 初始化endpoint
    endpoint.init();
}

public final void init() throws Exception {
    // Debug为false
    if (bindOnInit) {
        bindWithCleanup();
        bindState = BindState.BOUND_ON_INIT;
    }
    if (this.domain != null) {
        // Register endpoint (as ThreadPool - historical name)
        oname = new ObjectName(domain + ":type=ThreadPool,name="" + getName() + """);
        Registry.getRegistry(null, null).registerComponent(this, oname, null);
        ObjectName socketPropertiesOname = new ObjectName(domain +
                ":type=ThreadPool,name="" + getName() + "",subType=SocketProperties");
        socketProperties.setObjectName(socketPropertiesOname);
        Registry.getRegistry(null, null).registerComponent(socketProperties, socketPropertiesOname, null);
        for (SSLHostConfig sslHostConfig : findSslHostConfigs()) {
            registerJmx(sslHostConfig);
        }
    }
}

protected void startInternal() throws LifecycleException {
    // 发布启动事件
    fireLifecycleEvent(CONFIGURE_START_EVENT, null);
    setState(LifecycleState.STARTING);
    // 2.2.1.2.1 NamingResources启动
    globalNamingResources.start();
    // Start our defined Services
    synchronized (servicesLock) {
        for (int i = 0; i < services.length; i++) {
            // 2.2.1.2.2 Service启动
            services[i].start();
        }
    }
    if (periodicEventDelay > 0) {
        monitorFuture = getUtilityExecutor().scheduleWithFixedDelay(
                new Runnable() {
                    @Override
                    public void run() {
                        startPeriodicLifecycleEvent();
                    }
                }, 0, 60, TimeUnit.SECONDS);
    }
}

protected void startInternal() throws LifecycleException {
    fireLifecycleEvent(CONFIGURE_START_EVENT, null);
    setState(LifecycleState.STARTING);
}

protected void startInternal() throws LifecycleException {
    if(log.isInfoEnabled())
        log.info(sm.getString("standardService.start.name", this.name));
    setState(LifecycleState.STARTING);
    // Start our defined Container first
    if (engine != null) {
        synchronized (engine) {
            // 2.2.1.2.2.1 启动Engine
            engine.start();
        }
    }
    synchronized (executors) {
        for (Executor executor: executors) {
            // 2.2.1.2.2.3 启动Executor
            executor.start();
        }
    }
    // 2.2.1.2.2.4 启动MapperListener
    mapperListener.start();
    // Start our defined Connectors second
    synchronized (connectorsLock) {
        for (Connector connector: connectors) {
            // If it has already failed, don't try and start it
            if (connector.getState() != LifecycleState.FAILED) {
                // 2.2.1.2.2.5 启动connector
                connector.start();
            }
        }
    }
}

protected synchronized void startInternal() throws LifecycleException {
    // Log our server identification information
    if (log.isInfoEnabled()) {
        log.info(sm.getString("standardEngine.start", ServerInfo.getServerInfo()));
    }
    // Standard container startup
    super.startInternal();
}

protected synchronized void startInternal() throws LifecycleException {
    // Start our subordinate components, if any
    logger = null;
    getLogger();
    // Cluster与集群相关，SpringBoot项目中使用嵌入式Tomcat，不存在集群
    Cluster cluster = getClusterInternal();
    if (cluster instanceof Lifecycle) {
        ((Lifecycle) cluster).start();
    }
    // Realm与授权相关
    Realm realm = getRealmInternal();
    if (realm instanceof Lifecycle) {
        ((Lifecycle) realm).start();
    }
    // Start our child containers, if any
    // Container的类型是StandardHost
    Container children[] = findChildren();
    List<Future<Void>> results = new ArrayList<>();
    for (int i = 0; i < children.length; i++) {
        //异步初始化Host
        results.add(startStopExecutor.submit(new StartChild(children[i])));
    }
    MultiThrowable multiThrowable = null;
    for (Future<Void> result : results) {
        try {
            result.get();
        } catch (Throwable e) {
            log.error(sm.getString("containerBase.threadedStartFailed"), e);
            if (multiThrowable == null) {
                multiThrowable = new MultiThrowable();
            }
            multiThrowable.add(e);
        }
    }
    if (multiThrowable != null) {
        throw new LifecycleException(sm.getString("containerBase.threadedStartFailed"),
                multiThrowable.getThrowable());
    }
    // Start the Valves in our pipeline (including the basic), if any
    if (pipeline instanceof Lifecycle) {
        ((Lifecycle) pipeline).start();
    }
    setState(LifecycleState.STARTING);
    // Start our thread
    if (backgroundProcessorDelay > 0) {
        monitorFuture = Container.getService(ContainerBase.this).getServer()
                .getUtilityExecutor().scheduleWithFixedDelay(
                        new ContainerBackgroundProcessorMonitor(), 0, 60, TimeUnit.SECONDS);
    }
}

private static class StartChild implements Callable<Void>

public Void call() throws LifecycleException {
    child.start();
    return null;
}

protected synchronized void startInternal() throws LifecycleException {
    // Set error report valve
    String errorValve = getErrorReportValveClass();
    if ((errorValve != null) && (!errorValve.equals(""))) {
        try {
            boolean found = false;
            Valve[] valves = getPipeline().getValves();
            for (Valve valve : valves) {
                if (errorValve.equals(valve.getClass().getName())) {
                    found = true;
                    break;
                }
            }
            if(!found) {
                Valve valve =
                    (Valve) Class.forName(errorValve).getConstructor().newInstance();
                getPipeline().addValve(valve);
            }
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            log.error(sm.getString(
                    "standardHost.invalidErrorReportValveClass",
                    errorValve), t);
        }
    }
    super.startInternal();
}

protected synchronized void startInternal() throws LifecycleException {
    // ......
    // Start our child containers, if any
    Container children[] = findChildren();
    List<Future<Void>> results = new ArrayList<>();
    for (int i = 0; i < children.length; i++) {
        results.add(startStopExecutor.submit(new StartChild(children[i])));
    }

    synchronized (executors) {
        for (Executor executor: executors) {
            executor.start();
        }
    }

public void startInternal() throws LifecycleException {
    setState(LifecycleState.STARTING);
    Engine engine = service.getContainer();
    if (engine == null) {
        return;
    }
    // 获取当前部署的主机名（本地调试为localhost）
    findDefaultHost();
    // 把当前自身注册到Engine、Host、Context、Wrapper中
    addListeners(engine);
    // 取出的Container的类型为Host
    Container[] conHosts = engine.findChildren();
    for (Container conHost : conHosts) {
        Host host = (Host) conHost;
        if (!LifecycleState.NEW.equals(host.getState())) {
            // Registering the host will register the context and wrappers
            //将Host、Context、Wrapper注册到当前监听器中
            registerHost(host);
        }
    }
}

    // Start our defined Connectors second
    synchronized (connectorsLock) {
        for (Connector connector: connectors) {
            // If it has already failed, don't try and start it
            if (connector.getState() != LifecycleState.FAILED) {
                connector.start();
            }
        }
    }

@Override
public void start() {
   //启动Tomcat 容器
   this.webServer.start();
   this.running = true;
   this.applicationContext
         .publishEvent(new ServletWebServerInitializedEvent(this.webServer, this.applicationContext));
}

public void start() throws WebServerException {
    synchronized (this.monitor) {
        if (this.started) {
            return;
        }
        try {
            // 3.1.1 还原、启动Connector
            addPreviouslyRemovedConnectors();
            // 只拿一个Connector
            Connector connector = this.tomcat.getConnector();
            if (connector != null && this.autoStart) {
                // 3.1.2 延迟启动
                performDeferredLoadOnStartup();
            }
            // 检查Connector是否正常启动
            checkThatConnectorsHaveStarted();
            this.started = true;
            logger.info("Tomcat started on port(s): " + getPortsDescription(true) + " with context path '"
                    + getContextPath() + "'");
        }
        // catch ......
        finally {
            // 解除ClassLoader与TomcatEmbeddedContext的绑定关系
            Context context = findContext();
            ContextBindings.unbindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
        }
    }
}

private void addPreviouslyRemovedConnectors() {
    Service[] services = this.tomcat.getServer().findServices();
    for (Service service : services) {
        Connector[] connectors = this.serviceConnectors.get(service);
        if (connectors != null) {
            for (Connector connector : connectors) {
                // 添加并启动
                service.addConnector(connector);
                if (!this.autoStart) {
                    stopProtocolHandler(connector);
                }
            }
            this.serviceConnectors.remove(service);
        }
    }
}

public void addConnector(Connector connector) {
    synchronized (connectorsLock) {
        connector.setService(this);
        Connector results[] = new Connector[connectors.length + 1];
        System.arraycopy(connectors, 0, results, 0, connectors.length);
        results[connectors.length] = connector;
        connectors = results;
    }
    try {
        if (getState().isAvailable()) {
            // 启动Connector
            connector.start();
        }
    } catch (LifecycleException e) {
        throw new IllegalArgumentException(
                sm.getString("standardService.connector.startFailed", connector), e);
    }
    // Report this property change to interested listeners
    support.firePropertyChange("connector", null, connector);
}

protected void startInternal() throws LifecycleException {
    // Validate settings before starting
    if (getPortWithOffset() < 0) {
        throw new LifecycleException(sm.getString(
                "coyoteConnector.invalidPort", Integer.valueOf(getPortWithOffset())));
    }
    setState(LifecycleState.STARTING);
    try {
        // 启动ProtocolHandler
        protocolHandler.start();
    } catch (Exception e) {
        throw new LifecycleException(
                sm.getString("coyoteConnector.protocolHandlerStartFailed"), e);
    }
}

public void start() throws Exception {
    if (getLog().isInfoEnabled()) {
        getLog().info(sm.getString("abstractProtocolHandler.start", getName()));
        logPortOffset();
    }
    // 启动EndPoint
    endpoint.start();
    monitorFuture = getUtilityExecutor().scheduleWithFixedDelay(
            new Runnable() {
                @Override
                public void run() {
                    if (!isPaused()) {
                        startAsyncTimeout();
                    }
                }
            }, 0, 60, TimeUnit.SECONDS);
}

private void performDeferredLoadOnStartup() {
    try {
        for (Container child : this.tomcat.getHost().findChildren()) {
            if (child instanceof TomcatEmbeddedContext) {
                // 延迟启动Context
                ((TomcatEmbeddedContext) child).deferredLoadOnStartup();
            }
        }
    }
    catch (Exception ex) {
        if (ex instanceof WebServerException) {
            throw (WebServerException) ex;
        }
        throw new WebServerException("Unable to start embedded Tomcat connectors", ex);
    }
}