Spring Boot 内嵌Tomcat启动原理

1、Tomcat的自动装配

WebServerFactory自动配置类：负责创建Tomcat、Netty、Jetty等

org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration

@Configuration
@ConditionalOnWebApplication
@EnableConfigurationProperties(ServerProperties.class)
public class EmbeddedWebServerFactoryCustomizerAutoConfiguration {

	/**
	 * Nested configuration if Tomcat is being used.
	 */
	@Configuration
	@ConditionalOnClass({ Tomcat.class, UpgradeProtocol.class })
	public static class TomcatWebServerFactoryCustomizerConfiguration {

		// Tomcat工厂定制器
		@Bean
		public TomcatWebServerFactoryCustomizer tomcatWebServerFactoryCustomizer(
				Environment environment, ServerProperties serverProperties) {
			return new TomcatWebServerFactoryCustomizer(environment, serverProperties);
		}

	}

	/**
	 * Nested configuration if Jetty is being used.
	 */
	@Configuration
	@ConditionalOnClass({ Server.class, Loader.class, WebAppContext.class })
	public static class JettyWebServerFactoryCustomizerConfiguration {

		@Bean
		public JettyWebServerFactoryCustomizer jettyWebServerFactoryCustomizer(
				Environment environment, ServerProperties serverProperties) {
			return new JettyWebServerFactoryCustomizer(environment, serverProperties);
		}

	}

	/**
	 * Nested configuration if Undertow is being used.
	 */
	@Configuration
	@ConditionalOnClass({ Undertow.class, SslClientAuthMode.class })
	public static class UndertowWebServerFactoryCustomizerConfiguration {

		@Bean
		public UndertowWebServerFactoryCustomizer undertowWebServerFactoryCustomizer(
				Environment environment, ServerProperties serverProperties) {
			return new UndertowWebServerFactoryCustomizer(environment, serverProperties);
		}

	}

	/**
	 * Nested configuration if Netty is being used.
	 */
	@Configuration
	@ConditionalOnClass(HttpServer.class)
	public static class NettyWebServerFactoryCustomizerConfiguration {

		@Bean
		public NettyWebServerFactoryCustomizer nettyWebServerFactoryCustomizer(
				Environment environment, ServerProperties serverProperties) {
			return new NettyWebServerFactoryCustomizer(environment, serverProperties);
		}

	}

}

定制方法：设置容器的内容，把serverProperties的属性设置到tomcat的创建工厂中
org.springframework.boot.autoconfigure.web.servlet.TomcatWebServerFactoryCustomizer

	@Override
	public void customize(ConfigurableTomcatWebServerFactory factory) {
		ServerProperties properties = this.serverProperties;
		ServerProperties.Tomcat tomcatProperties = properties.getTomcat();
		PropertyMapper propertyMapper = PropertyMapper.get();
		propertyMapper.from(tomcatProperties::getBasedir).whenNonNull()
				.to(factory::setBaseDirectory);
		propertyMapper.from(tomcatProperties::getBackgroundProcessorDelay).whenNonNull()
				.as(Duration::getSeconds).as(Long::intValue)
				.to(factory::setBackgroundProcessorDelay);
		customizeRemoteIpValve(factory);
		propertyMapper.from(tomcatProperties::getMaxThreads).when(this::isPositive)
				.to((maxThreads) -> customizeMaxThreads(factory,
						tomcatProperties.getMaxThreads()));
		propertyMapper.from(tomcatProperties::getMinSpareThreads).when(this::isPositive)
				.to((minSpareThreads) -> customizeMinThreads(factory, minSpareThreads));
		propertyMapper.from(this::determineMaxHttpHeaderSize).whenNonNull()
				.asInt(DataSize::toBytes).when(this::isPositive)
				.to((maxHttpHeaderSize) -> customizeMaxHttpHeaderSize(factory,
						maxHttpHeaderSize));
		propertyMapper.from(tomcatProperties::getMaxSwallowSize).whenNonNull()
				.asInt(DataSize::toBytes)
				.to((maxSwallowSize) -> customizeMaxSwallowSize(factory, maxSwallowSize));
		propertyMapper.from(tomcatProperties::getMaxHttpPostSize).asInt(DataSize::toBytes)
				.when((maxHttpPostSize) -> maxHttpPostSize != 0)
				.to((maxHttpPostSize) -> customizeMaxHttpPostSize(factory,
						maxHttpPostSize));
		propertyMapper.from(tomcatProperties::getAccesslog)
				.when(ServerProperties.Tomcat.Accesslog::isEnabled)
				.to((enabled) -> customizeAccessLog(factory));
		propertyMapper.from(tomcatProperties::getUriEncoding).whenNonNull()
				.to(factory::setUriEncoding);
		propertyMapper.from(properties::getConnectionTimeout).whenNonNull()
				.to((connectionTimeout) -> customizeConnectionTimeout(factory,
						connectionTimeout));
		propertyMapper.from(tomcatProperties::getMaxConnections).when(this::isPositive)
				.to((maxConnections) -> customizeMaxConnections(factory, maxConnections));
		propertyMapper.from(tomcatProperties::getAcceptCount).when(this::isPositive)
				.to((acceptCount) -> customizeAcceptCount(factory, acceptCount));
		customizeStaticResources(factory);
		customizeErrorReportValve(properties.getError(), factory);
	}

2、ServletWebServer工厂自动配置

org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration

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

// 定制Servlet 的信息
	@Bean
	public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(
			ServerProperties serverProperties) {
		return new ServletWebServerFactoryCustomizer(serverProperties);
	}

// 定制Tomcat 额外相关信息
	@Bean
	@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
	public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
			ServerProperties serverProperties) {
		return new TomcatServletWebServerFactoryCustomizer(serverProperties);
	}

	/**
	 * 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);
			}
		}

	}

}

org.springframework.boot.autoconfigure.web.servlet.TomcatServletWebServerFactoryCustomizer

public class TomcatServletWebServerFactoryCustomizer
		implements WebServerFactoryCustomizer, Ordered {

	private final ServerProperties serverProperties;

	public TomcatServletWebServerFactoryCustomizer(ServerProperties serverProperties) {
		this.serverProperties = serverProperties;
	}

	@Override
	public int getOrder() {
		return 0;
	}

// 配置Tomcat 的额外信息，redirectContextRoot和useRelativeRedirects
	@Override
	public void customize(TomcatServletWebServerFactory factory) {
		ServerProperties.Tomcat tomcatProperties = this.serverProperties.getTomcat();
		if (!ObjectUtils.isEmpty(tomcatProperties.getAdditionalTldSkipPatterns())) {
			factory.getTldSkipPatterns()
					.addAll(tomcatProperties.getAdditionalTldSkipPatterns());
		}
		if (tomcatProperties.getRedirectContextRoot() != null) {
			customizeRedirectContextRoot(factory,
					tomcatProperties.getRedirectContextRoot());
		}
		if (tomcatProperties.getUseRelativeRedirects() != null) {
			customizeUseRelativeRedirects(factory,
					tomcatProperties.getUseRelativeRedirects());
		}
	}

// 负责定制servlet信息，包含端口、上下文、路径、应用名、Session配置、Servlet携带的初始化变量等等
	private void customizeRedirectContextRoot(ConfigurableTomcatWebServerFactory factory,
			boolean redirectContextRoot) {
		factory.addContextCustomizers((context) -> context
				.setMapperContextRootRedirectEnabled(redirectContextRoot));
	}

	private void customizeUseRelativeRedirects(ConfigurableTomcatWebServerFactory factory,
			boolean useRelativeRedirects) {
		factory.addContextCustomizers(
				(context) -> context.setUseRelativeRedirects(useRelativeRedirects));
	}

}

@Import(ServletWebServerFactoryConfiguration.EmbeddedTomcat.class)内嵌Tomcat

	@Configuration
	@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
	@ConditionalOnMissingBean(value = ServletWebServerFactory.class,
			search = SearchStrategy.CURRENT)
	public static class EmbeddedTomcat {

		@Bean
		public TomcatServletWebServerFactory tomcatServletWebServerFactory() {
			return new TomcatServletWebServerFactory();
		}
	}

TomcatServletWebServerFactory.getWebServer()拿到WebServer 实例

@Override
	public WebServer getWebServer(ServletContextInitializer... initializers) {
		Tomcat tomcat = new Tomcat();
		File baseDir = (this.baseDirectory != null) ? this.baseDirectory
				: createTempDir("tomcat");
		tomcat.setBaseDir(baseDir.getAbsolutePath());
		Connector connector = new Connector(this.protocol);
		tomcat.getService().addConnector(connector);
		customizeConnector(connector);
		tomcat.setConnector(connector);
		tomcat.getHost().setAutoDeploy(false);
		configureEngine(tomcat.getEngine());
		for (Connector additionalConnector : this.additionalTomcatConnectors) {
			tomcat.getService().addConnector(additionalConnector);
		}
		prepareContext(tomcat.getHost(), initializers);
		return getTomcatWebServer(tomcat);
	}

3、启动Tomcat

Application#run开始：

public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection exceptionReporters = new ArrayList<>();
		configureHeadlessProperty();
		SpringApplicationRunListeners listeners = getRunListeners(args);
		listeners.starting();
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(
					args);
			ConfigurableEnvironment environment = prepareEnvironment(listeners,
					applicationArguments);
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			exceptionReporters = getSpringFactoriesInstances(
					SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
					//创建上下文
			prepareContext(context, environment, listeners, applicationArguments,
					printedBanner);
					//刷新上下文
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass)
						.logStarted(getApplicationLog(), stopWatch);
			}
			listeners.started(context);
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}

	private void refreshContext(ConfigurableApplicationContext context) {
		refresh(context);
		if (this.registerShutdownHook) {
			try {
				context.registerShutdownHook();
			}
			catch (AccessControlException ex) {
				// Not allowed in some environments.
			}
		}
	}

	protected void refresh(ApplicationContext applicationContext) {
		Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
		((AbstractApplicationContext) applicationContext).refresh();
	}

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

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

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

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

				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

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

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

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

				// Initialize other special beans in specific context subclasses.
				//调用子容器onRefresh方法
				onRefresh();

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

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

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

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

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

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

				// Propagate exception to caller.
				throw ex;
			}

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

org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext

	@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) {
			ServletWebServerFactory factory = getWebServerFactory();
			//创建Tomcat
			this.webServer = factory.getWebServer(getSelfInitializer());
		}
		else if (servletContext != null) {
			try {
				getSelfInitializer().onStartup(servletContext);
			}
			catch (ServletException ex) {
				throw new ApplicationContextException("Cannot initialize servlet context",
						ex);
			}
		}
		initPropertySources();
	}

@Override
	public WebServer getWebServer(ServletContextInitializer... initializers) {
		Tomcat tomcat = new Tomcat();
		File baseDir = (this.baseDirectory != null) ? this.baseDirectory
				: createTempDir("tomcat");
		tomcat.setBaseDir(baseDir.getAbsolutePath());
		//创建Connector 
		Connector connector = new Connector(this.protocol);
		//将Connector 添加到tomcat中
		tomcat.getService().addConnector(connector);
		customizeConnector(connector);
		tomcat.setConnector(connector);
		tomcat.getHost().setAutoDeploy(false);
		//添加Engine容器
		configureEngine(tomcat.getEngine());
		for (Connector additionalConnector : this.additionalTomcatConnectors) {
			tomcat.getService().addConnector(additionalConnector);
		}
		prepareContext(tomcat.getHost(), initializers);
		return getTomcatWebServer(tomcat);
	}


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

org.springframework.boot.web.embedded.tomcat.TomcatWebServer

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

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

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

				// Start the server to trigger initialization listeners
				//通过Tomcat类的start方法启动，其实还是调用了TomcatWebServer的start方法
				this.tomcat.start();

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

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

				// Unlike Jetty, all Tomcat threads are daemon threads. We create a
				// blocking non-daemon to stop immediate shutdown
				startDaemonAwaitThread();
			}
			catch (Exception ex) {
				stopSilently();
				throw new WebServerException("Unable to start embedded Tomcat", ex);
			}
		}
	}


//启动Tomcat

	 @Override
	public void start() throws WebServerException {
		synchronized (this.monitor) {
			if (this.started) {
				return;
			}
			try {
				addPreviouslyRemovedConnectors();
				Connector connector = this.tomcat.getConnector();
				if (connector != null && this.autoStart) {
					performDeferredLoadOnStartup();
				}
				checkThatConnectorsHaveStarted();
				this.started = true;
				logger.info("Tomcat started on port(s): " + getPortsDescription(true)
						+ " with context path '" + getContextPath() + "'");
			}
			catch (ConnectorStartFailedException ex) {
				stopSilently();
				throw ex;
			}
			catch (Exception ex) {
				throw new WebServerException("Unable to start embedded Tomcat server",
						ex);
			}
			finally {
				Context context = findContext();
				ContextBindings.unbindClassLoader(context, context.getNamingToken(),
						getClass().getClassLoader());
			}
		}
	}


//关闭Tomcat

@Override
	public void stop() throws WebServerException {
		synchronized (this.monitor) {
			boolean wasStarted = this.started;
			try {
				this.started = false;
				try {
					stopTomcat();
					this.tomcat.destroy();
				}
				catch (LifecycleException ex) {
					// swallow and continue
				}
			}
			catch (Exception ex) {
				throw new WebServerException("Unable to stop embedded Tomcat", ex);
			}
			finally {
				if (wasStarted) {
					containerCounter.decrementAndGet();
				}
			}
		}
	}