springMvc源码解析

入口：找到springboot的自动配置，将DispatcherServlet和DispatcherServletRegistrationBean注入spring容器（DispatcherServletRegistrationBean间接实现了ServletContextInitializer接口，最终ServletContextInitializer的onStartup()方法会被调用），将DispatcherServlet设置到ServletContext里，设置loadOnStartup属性（默认值-1，表示Servlet对象在用户访问时创建）和addUrlMappings（默认"/"）

		@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,webMvcProperties.getServlet().getPath());registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());multipartConfig.ifAvailable(registration::setMultipartConfig);return registration;}

		@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {//设置UrlMappings 默认"/"DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,webMvcProperties.getServlet().getPath());registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);//设置默认值-1registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());multipartConfig.ifAvailable(registration::setMultipartConfig);return registration;}

DispatcherServletRegistrationBean 在dispatcherServlet存在的情况下创建

一、首先看看springboot是怎么启动tomcat的

1.从SpringApplication.run(WebApplicaiton.class,args)，这个入口进入

	public ConfigurableApplicationContext run(String... args) {long startTime = System.nanoTime();DefaultBootstrapContext bootstrapContext = createBootstrapContext();ConfigurableApplicationContext context = null;configureHeadlessProperty();SpringApplicationRunListeners listeners = getRunListeners(args);listeners.starting(bootstrapContext, this.mainApplicationClass);try {ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);configureIgnoreBeanInfo(environment);Banner printedBanner = printBanner(environment);context = createApplicationContext();context.setApplicationStartup(this.applicationStartup);prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);refreshContext(context);afterRefresh(context, applicationArguments);Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);}listeners.started(context, timeTakenToStartup);callRunners(context, applicationArguments);}catch (Throwable ex) {handleRunFailure(context, ex, listeners);throw new IllegalStateException(ex);}try {Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);listeners.ready(context, timeTakenToReady);}catch (Throwable ex) {handleRunFailure(context, ex, null);throw new IllegalStateException(ex);}return context;}

2.找到refreshContext方法并进入

	private void refreshContext(ConfigurableApplicationContext context) {if (this.registerShutdownHook) {shutdownHook.registerApplicationContext(context);}refresh(context);}

3.找到refresh方法并进入

	protected void refresh(ConfigurableApplicationContext applicationContext) {applicationContext.refresh();}

4.进入到AbstractApplicationContext下的refresh()

	public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");// 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);StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");// Invoke factory processors registered as beans in the context.invokeBeanFactoryPostProcessors(beanFactory);// Register bean processors that intercept bean creation.registerBeanPostProcessors(beanFactory);beanPostProcess.end();// Initialize message source for this context.initMessageSource();// Initialize event multicaster for this context.initApplicationEventMulticaster();// Initialize other special beans in specific context subclasses.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();contextRefresh.end();}}}

5.我们进入ServletWebServerApplicationContext下的onRefresh方法

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

6.进入createWebServer方法

	private void createWebServer() {WebServer webServer = this.webServer;ServletContext servletContext = getServletContext();if (webServer == null && servletContext == null) {StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");ServletWebServerFactory factory = getWebServerFactory();createWebServer.tag("factory", factory.getClass().toString());// 调用spring容器里所有ServletContextInitializer接口实现类的onStartup方法（包含DispatcherServletAutoConfiguration配置类配置的DispatcherServletRegistrationBean类）// 配置DispatcherServlet到tomcat上下文this.webServer = factory.getWebServer(getSelfInitializer());createWebServer.end();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);}}initPropertySources();}

7.再进入TomcatServletWebServerFactory的getWebServer方法(把DispatcherServletRegistrationBean中持有的DispatcherServlet注册到Tomcat中,然后Tomcat会回调DispatcherServlet的init方法把初始化SpringMVC的所有组件)

	public WebServer getWebServer(ServletContextInitializer... initializers) {if (this.disableMBeanRegistry) {Registry.disableRegistry();}Tomcat tomcat = new Tomcat();File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");tomcat.setBaseDir(baseDir.getAbsolutePath());for (LifecycleListener listener : this.serverLifecycleListeners) {tomcat.getServer().addLifecycleListener(listener);}Connector connector = new Connector(this.protocol);connector.setThrowOnFailure(true);tomcat.getService().addConnector(connector);customizeConnector(connector);tomcat.setConnector(connector);tomcat.getHost().setAutoDeploy(false);configureEngine(tomcat.getEngine());for (Connector additionalConnector : this.additionalTomcatConnectors) {tomcat.getService().addConnector(additionalConnector);}//把DispatcherServletRegistrationBean中持有的DispatcherServlet注册到Tomcat中prepareContext(tomcat.getHost(), initializers);return getTomcatWebServer(tomcat);}

8.prepareContext的configureContext()方法配置相关环境

	protected void configureContext(Context context, ServletContextInitializer[] initializers) {TomcatStarter starter = new TomcatStarter(initializers);if (context instanceof TomcatEmbeddedContext) {TomcatEmbeddedContext embeddedContext = (TomcatEmbeddedContext) context;embeddedContext.setStarter(starter);embeddedContext.setFailCtxIfServletStartFails(true);}context.addServletContainerInitializer(starter, NO_CLASSES);for (LifecycleListener lifecycleListener : this.contextLifecycleListeners) {context.addLifecycleListener(lifecycleListener);}for (Valve valve : this.contextValves) {context.getPipeline().addValve(valve);}for (ErrorPage errorPage : getErrorPages()) {org.apache.tomcat.util.descriptor.web.ErrorPage tomcatErrorPage = new org.apache.tomcat.util.descriptor.web.ErrorPage();tomcatErrorPage.setLocation(errorPage.getPath());tomcatErrorPage.setErrorCode(errorPage.getStatusCode());tomcatErrorPage.setExceptionType(errorPage.getExceptionName());context.addErrorPage(tomcatErrorPage);}for (MimeMappings.Mapping mapping : getMimeMappings()) {context.addMimeMapping(mapping.getExtension(), mapping.getMimeType());}configureSession(context);configureCookieProcessor(context);new DisableReferenceClearingContextCustomizer().customize(context);for (String webListenerClassName : getWebListenerClassNames()) {context.addApplicationListener(webListenerClassName);}for (TomcatContextCustomizer customizer : this.tomcatContextCustomizers) {customizer.customize(context);}}

9.进入getTomcatWebServer(tomcat)得到web的服务端，然后进行初始化

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

	public TomcatWebServer(Tomcat tomcat, boolean autoStart, Shutdown shutdown) {Assert.notNull(tomcat, "Tomcat Server must not be null");this.tomcat = tomcat;this.autoStart = autoStart;this.gracefulShutdown = (shutdown == Shutdown.GRACEFUL) ? new GracefulShutdown(tomcat) : null;initialize();}

10.初始化

	private void initialize() throws WebServerException {logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));synchronized (this.monitor) {try {addInstanceIdToEngineName();Context context = findContext();context.addLifecycleListener((event) -> {if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {// Remove service connectors so that protocol binding doesn't// happen when the service is started.removeServiceConnectors();}});// Start the server to trigger initialization listenersthis.tomcat.start();// We can re-throw failure exception directly in the main threadrethrowDeferredStartupExceptions();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 shutdownstartDaemonAwaitThread();}catch (Exception ex) {stopSilently();destroySilently();throw new WebServerException("Unable to start embedded Tomcat", ex);}}}

11.调用 this.tomcat.start()方法启动tomcat

方法调用流程图：

tomcat请求流程分析参考：
https://blog.csdn.net/qq_43188744/article/details/108083683
其中主要是StandardWrapper.allocate()方法，如果发现severlet没有实例化则会进行initServlet(instance)

二、springmvc处理请求

1.DispatcherServlet的初始化

初始化时会进入DispatcherServlet的init()方法
然后会执行onRefresh()方法进行初始化

	protected void onRefresh(ApplicationContext context) {initStrategies(context);}protected void initStrategies(ApplicationContext context) {initMultipartResolver(context);initLocaleResolver(context);initThemeResolver(context);initHandlerMappings(context);initHandlerAdapters(context);initHandlerExceptionResolvers(context);initRequestToViewNameTranslator(context);initViewResolvers(context);initFlashMapManager(context);}

2.处理请求

1.进入到HttpServlet 的service，这里会处理get、post等请求

    protected void service(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {String method = req.getMethod();if (method.equals(METHOD_GET)) {long lastModified = getLastModified(req);if (lastModified == -1) {// servlet doesn't support if-modified-since, no reason// to go through further expensive logicdoGet(req, resp);} else {long ifModifiedSince;try {ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);} catch (IllegalArgumentException iae) {// Invalid date header - proceed as if none was setifModifiedSince = -1;}if (ifModifiedSince < (lastModified / 1000 * 1000)) {// If the servlet mod time is later, call doGet()// Round down to the nearest second for a proper compare// A ifModifiedSince of -1 will always be lessmaybeSetLastModified(resp, lastModified);doGet(req, resp);} else {resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);}}} else if (method.equals(METHOD_HEAD)) {long lastModified = getLastModified(req);maybeSetLastModified(resp, lastModified);doHead(req, resp);} else if (method.equals(METHOD_POST)) {doPost(req, resp);} else if (method.equals(METHOD_PUT)) {doPut(req, resp);} else if (method.equals(METHOD_DELETE)) {doDelete(req, resp);} else if (method.equals(METHOD_OPTIONS)) {doOptions(req,resp);} else if (method.equals(METHOD_TRACE)) {doTrace(req,resp);} else {//// Note that this means NO servlet supports whatever// method was requested, anywhere on this server.//String errMsg = lStrings.getString("http.method_not_implemented");Object[] errArgs = new Object[1];errArgs[0] = method;errMsg = MessageFormat.format(errMsg, errArgs);resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);}}

2.进入DispatcherServlet 的doService–>doDispatch()方法，doDispatch()是核心

	/*** Process the actual dispatching to the handler.* <p>The handler will be obtained by applying the servlet's HandlerMappings in order.* The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters* to find the first that supports the handler class.* <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers* themselves to decide which methods are acceptable.* @param request current HTTP request* @param response current HTTP response* @throws Exception in case of any kind of processing failure*/@SuppressWarnings("deprecation")protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {HttpServletRequest processedRequest = request;HandlerExecutionChain mappedHandler = null;boolean multipartRequestParsed = false;WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);try {ModelAndView mv = null;Exception dispatchException = null;try {processedRequest = checkMultipart(request);multipartRequestParsed = (processedRequest != request);// Determine handler for the current request.mappedHandler = getHandler(processedRequest);if (mappedHandler == null) {noHandlerFound(processedRequest, response);return;}// Determine handler adapter for the current request.HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// Process last-modified header, if supported by the handler.String method = request.getMethod();boolean isGet = HttpMethod.GET.matches(method);if (isGet || HttpMethod.HEAD.matches(method)) {long lastModified = ha.getLastModified(request, mappedHandler.getHandler());if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {return;}}if (!mappedHandler.applyPreHandle(processedRequest, response)) {return;}// Actually invoke the handler.//执行具体HandlerAdapter对象的handle()方法mv = ha.handle(processedRequest, response, mappedHandler.getHandler());if (asyncManager.isConcurrentHandlingStarted()) {return;}applyDefaultViewName(processedRequest, mv);mappedHandler.applyPostHandle(processedRequest, response, mv);}catch (Exception ex) {dispatchException = ex;}catch (Throwable err) {// As of 4.3, we're processing Errors thrown from handler methods as well,// making them available for @ExceptionHandler methods and other scenarios.dispatchException = new NestedServletException("Handler dispatch failed", err);}processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);}catch (Exception ex) {triggerAfterCompletion(processedRequest, response, mappedHandler, ex);}catch (Throwable err) {triggerAfterCompletion(processedRequest, response, mappedHandler,new NestedServletException("Handler processing failed", err));}finally {if (asyncManager.isConcurrentHandlingStarted()) {// Instead of postHandle and afterCompletionif (mappedHandler != null) {mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}}else {// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}}

3. 进入getHandler(processedRequest)

	protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {if (this.handlerMappings != null) {for (HandlerMapping mapping : this.handlerMappings) {HandlerExecutionChain handler = mapping.getHandler(request);if (handler != null) {return handler;}}}return null;}

这里的this.handlerMappings默认加在的是DispatcherServlet.properties里面定义的
三个handlerMappings：

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\org.springframework.web.servlet.function.support.RouterFunctionMapping

在初始化调用initHandlerMappings(context)，进行初始化的。

4.以AbstractHandlerMapping为例子进入：getHandler方法

	public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {Object handler = getHandlerInternal(request);if (handler == null) {handler = getDefaultHandler();}if (handler == null) {return null;}// Bean name or resolved handler?if (handler instanceof String) {String handlerName = (String) handler;handler = obtainApplicationContext().getBean(handlerName);}// Ensure presence of cached lookupPath for interceptors and othersif (!ServletRequestPathUtils.hasCachedPath(request)) {initLookupPath(request);}HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);if (logger.isTraceEnabled()) {logger.trace("Mapped to " + handler);}else if (logger.isDebugEnabled() && !DispatcherType.ASYNC.equals(request.getDispatcherType())) {logger.debug("Mapped to " + executionChain.getHandler());}if (hasCorsConfigurationSource(handler) || CorsUtils.isPreFlightRequest(request)) {CorsConfiguration config = getCorsConfiguration(handler, request);if (getCorsConfigurationSource() != null) {CorsConfiguration globalConfig = getCorsConfigurationSource().getCorsConfiguration(request);config = (globalConfig != null ? globalConfig.combine(config) : config);}if (config != null) {config.validateAllowCredentials();}executionChain = getCorsHandlerExecutionChain(request, executionChain, config);}return executionChain;}

5.进入AbstractHandlerMethodMapping的getHandlerInternal(request)，通过initLookupPath(request)查找HandlerMethod

	protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {String lookupPath = initLookupPath(request);this.mappingRegistry.acquireReadLock();try {HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);}finally {this.mappingRegistry.releaseReadLock();}}

6.回到doDispatch，以AbstractHandlerMethodAdapter为例，执行ha.handle

	public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {return handleInternal(request, response, (HandlerMethod) handler);}

7.RequestMappingHandlerAdapter的handleInternal

	protected ModelAndView handleInternal(HttpServletRequest request,HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {ModelAndView mav;checkRequest(request);// Execute invokeHandlerMethod in synchronized block if required.if (this.synchronizeOnSession) {HttpSession session = request.getSession(false);if (session != null) {Object mutex = WebUtils.getSessionMutex(session);synchronized (mutex) {mav = invokeHandlerMethod(request, response, handlerMethod);}}else {// No HttpSession available -> no mutex necessarymav = invokeHandlerMethod(request, response, handlerMethod);}}else {// No synchronization on session demanded at all...mav = invokeHandlerMethod(request, response, handlerMethod);}if (!response.containsHeader(HEADER_CACHE_CONTROL)) {if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);}else {prepareResponse(response);}}return mav;}

8.进入invokeHandlerMethod

	protected ModelAndView invokeHandlerMethod(HttpServletRequest request,HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {ServletWebRequest webRequest = new ServletWebRequest(request, response);try {WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);if (this.argumentResolvers != null) {invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);}if (this.returnValueHandlers != null) {invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);}invocableMethod.setDataBinderFactory(binderFactory);invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);ModelAndViewContainer mavContainer = new ModelAndViewContainer();mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));modelFactory.initModel(webRequest, mavContainer, invocableMethod);mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);asyncWebRequest.setTimeout(this.asyncRequestTimeout);WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);asyncManager.setTaskExecutor(this.taskExecutor);asyncManager.setAsyncWebRequest(asyncWebRequest);asyncManager.registerCallableInterceptors(this.callableInterceptors);asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);if (asyncManager.hasConcurrentResult()) {Object result = asyncManager.getConcurrentResult();mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];asyncManager.clearConcurrentResult();LogFormatUtils.traceDebug(logger, traceOn -> {String formatted = LogFormatUtils.formatValue(result, !traceOn);return "Resume with async result [" + formatted + "]";});invocableMethod = invocableMethod.wrapConcurrentResult(result);}invocableMethod.invokeAndHandle(webRequest, mavContainer);if (asyncManager.isConcurrentHandlingStarted()) {return null;}return getModelAndView(mavContainer, modelFactory, webRequest);}finally {webRequest.requestCompleted();}}

9.进入invocableMethod.invokeAndHandle(webRequest, mavContainer)

	public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,Object... providedArgs) throws Exception {//处理请求，通过反射调用方法Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);setResponseStatus(webRequest);if (returnValue == null) {if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {disableContentCachingIfNecessary(webRequest);mavContainer.setRequestHandled(true);return;}}else if (StringUtils.hasText(getResponseStatusReason())) {mavContainer.setRequestHandled(true);return;}mavContainer.setRequestHandled(false);Assert.state(this.returnValueHandlers != null, "No return value handlers");try {//处理返回值，通过MessageConverters转换为想要的格式this.returnValueHandlers.handleReturnValue(returnValue, getReturnValueType(returnValue), mavContainer, webRequest);}catch (Exception ex) {if (logger.isTraceEnabled()) {logger.trace(formatErrorForReturnValue(returnValue), ex);}throw ex;}}