ServletWebServerApplicationContext如何创建Web容器Tomcat
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今天小编给大家分享一下ServletWebServerApplicationContext如何创建Web容器Tomcat的相关知识点，内容详细，逻辑清晰，相信大部分人都还太了解这方面的知识，所以分享这篇文章给大家参考一下，希望大家阅读完这篇文章后有所收获，下面我们一起来了解一下吧。
正文
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。
@Overrideprotected 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; } 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
@Configurationclass 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()); }}2.1.1 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(); }}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(); } }}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;}初始化executor
它还是调的父类 LifecycleMBeanBase 的方法
protected void initInternal() throws LifecycleException { super.initInternal();}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()); }}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); }}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 ：
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。
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
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); }}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);}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(); } } }}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：
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
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(); } }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); } }}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(); } } }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()
@Overridepublic 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。
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); }}以上就是“ServletWebServerApplicationContext如何创建Web容器Tomcat”这篇文章的所有内容，感谢各位的阅读！相信大家阅读完这篇文章都有很大的收获，小编每天都会为大家更新不同的知识，如果还想学习更多的知识，请关注编程网行业资讯频道。
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