ServletWebServerApplicationContext实现了父类AbstractApplicationContext的onRefresh模板方法，在这里进行了拓展创建了Web容器。

@Override
protected void onRefresh() {
   super.onRefresh();
   try {
      createWebServer();
   }
   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) {
      //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();
}

一、获取Web服务器工厂

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);
}

这里的Web服务器工厂是通过ServletWebServerFactoryAutoConfiguration自动配置类导入进来的。

@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);
         }
      }

   }

}

1.1 选择导入Web工厂

@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();
        }
    }
}

二、getWebServer：获取Web服务

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);
}

2.1 创建TomcatEmbeddedContext

（注释均已在源码中标注好，小伙伴们对哪一步感兴趣可以借助IDE自己动手Debug体会一下实现）

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);
}

2.2. 创建TomcatWebServer

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

进入TomcatWebServer构造方法中：

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();
}

初始化TomcatWebServer

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);
      }
   }
}

2.2.1 启动Tomcat

创建和初始化Server和Service

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

启动服务

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());
    }
}

2.2.1.1 初始化Server

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());
    }
}

初始化Server

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();
    }
}

2.2.1.1.1 初始化Service

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());
    }
}

初始化Service

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();
        }
    }
}

2.2.1.1.1.1 初始化engine

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;
}

2.2.1.1.1.2 初始化executor

它还是调的父类 LifecycleMBeanBase 的方法

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

2.2.1.1.1.3 初始化mapperListener

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());
    }
}

2.2.1.1.1.4 初始化connector

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);
    }
}

2.2.1.1.1.5初始化protocolHandler

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();
}

Debug发现这个 upgradeProtocols 为空，直接走下面父类（AbstractProtocol）的 init 方法：

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();
}

上面又是一堆初始化，这个咱暂且不关注，注意最底下有一个 endpoint.init ：

2.2.1.1.1.6 初始化endpoint

来到 AbstractEndPoint ：

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);
        }
    }
}

这里面又是初始化 oname ，又是配置 socketProperties 的，但这里面再也没见到 init 方法，证明这部分初始化过程已经结束了。

2.2.1.1.2 初始化小结

嵌入式 Tomcat 的组件初始化步骤顺序如下：

Server
Service
Engine
Executor
MapperListener
Connector
Protocol
EndPoint

2.2.1.2 startInternal：启动Internal

startInternal 方法中有两部分启动：globalNamingResources 启动，services 启动。分别来看：

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);
    }
}

2.2.1.2.1 NamingResources启动

只是发布事件和设置状态而已

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

2.2.1.2.2 Service启动

依次启动 Engine 、Executor 、MapperListener 、Connector

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();
            }
        }
    }
}

2.2.1.2.2.1 启动Engine

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();
}

它直接调的父类 ContainerBase 的 startInternal 方法：

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);
    }
}

StartChild 实现了带返回值的异步多线程接口 Callable 核心方法就是在 call

private static class StartChild implements Callable<Void>

它实现了带返回值的异步多线程接口 Callable ！那里面的核心方法就是 call ：

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

它在这里初始化 child，而通过Debug得知 child 的类型是 StandardHost，故来到 StandardHost 的 start 方法：

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();
}

上面的一个大if结构是设置错误提示页面的，下面又调父类的 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])));
    }

又回来了。。。因为一个 Host 包含一个 Context 。

Host 搜索children就会搜到它下面的 Context ，之后又是下面的初始化过程，进入 Context 的初始化：

2.2.1.2.2.2 启动TomcatEmbeddedContext

在TomcatEmbeddedContext有如下组件被调用了 start 方法：

StandardRoot
DirResourceSet
WebappLoader
JarResourceSet
StandardWrapper
StandardPineline
StandardWrapperValve
NonLoginAuthenticator
StandardContextValve
StandardManager
LazySessionIdGenerator

2.2.1.2.2.3 启动Executor

但由于 Executor 没有实现 startInternal 方法，所以不会启动

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

2.2.1.2.2.4 启动MapperListener

接下来启动 MapperListener ：

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);
        }
    }
}

2.2.1.2.2.5 启动Connector

最后一步是启动 Connector 。

    // 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();
            }
        }
    }

2.2.1.2.3 启动总结

启动过程依次启动了如下组件：

NamingResources
Service
Engine
Host
Context
Wrapper
Executor
MapperListener

三、注册Bean生命周期

3.1 WebServerStartStopLifecycle（Web服务器启动-停止生命周期）

WebServerStartStopLifecycle实现了Lifecycle，在容器刷新完成时会调用finishRefresh()

@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());
        }
    }
}

3.1.1 addPreviouslyRemovedConnectors：启动Connector

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);
        }
    }
}

可以发现它将一个缓存区的 Connector 一个一个取出放入 Service 中。注意在 service.addConnector 中有顺便启动的部分：

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);
}

前面的部分是取出 Connector ，并与 Service 绑定，之后中间部分的try块，会启动 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);
    }
}

Connector 的启动会引发 ProtocolHandler 的启动：

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);
}

ProtocolHandler 的启动会引发 EndPoint 的启动，至此所有组件均已启动完毕。

3.1.2 performDeferredLoadOnStartup：延迟启动

这里面会延迟启动 TomcatEmbeddedContext

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);
    }
}

四、初始化上下文环境

这里在Spring中已经刷新过一次，详情：在文章 juejin.cn/post/720253… 的 prepareRefresh：初始化前的预处理中

今天的文章ServletWebServerApplicationContext创建Web容器（Tomcat）分享到此就结束了，感谢您的阅读。

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ServletWebServerApplicationContext创建Web容器（Tomcat）