SpringMVC具体执行流程

1. 用户发送请求至前端控制器DispatcherServlet

2. DispatcherServlet收到请求调用处理器映射器HandlerMapping
   处理器映射器根据请求url找到具体的处理器，生成处理器执行链HandlerExecutionChain(包括处理器对象和处理器拦截器)一并返回给DispatcherServlet

3. DispatcherServlet根据处理器Handler获取处理器适配器
   HandlerAdapter,执行HandlerAdapter处理一系列的操作，如：参数封装，数据格式转换，数据验证等操作

4. HandlerAdapter执行处理器Handler(Controller，也叫页面控制器)
   Handler执行完成返回ModelAndView, 将执行结果ModelAndView返回到DispatcherServlet

5. DispatcherServlet将ModelAndView传给ViewReslover视图解析器
   ViewReslover解析后返回具体View

6. DispatcherServlet对View进行渲染视图（即将模型数据model填充至视图中）

7. DispatcherServlet响应用户

一个URL请求执行流程

1. 执行 HttpServlet 的 service(HttpServletRequest req, HttpServletResponse resp) 方法

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 = req.getDateHeader(HEADER_IFMODSINCE);if (ifModifiedSince < lastModified) {// 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. 执行demo请求 HttpServlet的doGet(HttpServletRequest req, HttpServletResponse resp)方法 子类 FrameworkServlet

    @Overridepublic void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {process(request, response);}

3. FrameworkServlet的process方法

	protected final void processRequest(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {。。。。。。。doService(request, response);。。。。。。。}

4. FrameworkServlet 子类 DispatcherServlet 的doService(HttpServletRequest request, HttpServletResponse response)方法

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {.......doDispatch(request, response);.......
}

5. DispatcherServlet的doDispatch(HttpServletRequest request, HttpServletResponse response)方法 主方法（重点）

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 {//文件上传相关processedRequest = checkMultipart(request);multipartRequestParsed = (processedRequest != request);// DispatcherServlet收到请求调用处理器映射器HandlerMapping// 处理器映射器根据请求url找到具体的处理器，生成处理器执行链HandlerExecutionChain(包括处理器对象和处理器拦截器)// 并返回给DispatcherServletmappedHandler = getHandler(processedRequest);if (mappedHandler == null) {noHandlerFound(processedRequest, response);return;}// DispatcherServlet根据处理器Handler获取处理器适配器HandlerAdapterHandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// Process last-modified header, if supported by the handler.  HTTP缓存相关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;}}// 前置拦截器if (!mappedHandler.applyPreHandle(processedRequest, response)) {// 返回false就不进行后续处理了return;}// 执行HandlerAdapter处理一系列的操作，如：参数封装，数据格式转换，数据验证等操作// 执行处理器Handler(Controller，也叫页面控制器)// Handler执行完成返回ModelAndView// HandlerAdapter将Handler执行结果ModelAndView返回到DispatcherServletmv = ha.handle(processedRequest, response, mappedHandler.getHandler());if (asyncManager.isConcurrentHandlingStarted()) {return;}// 如果没有视图，给你设置默认视图json忽略applyDefaultViewName(processedRequest, mv);//后置拦截器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);}// DispatcherServlet将ModelAndView传给ViewReslover视图解析器// ViewReslover解析后返回具体View// DispatcherServlet对View进行渲染视图（即将模型数据model填充至视图中）// DispatcherServlet响应用户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);}}}}

默认的HandlerMapping根据URL匹配选择合适的
RequestMapping
HandlerMapping
SimpleUrlHandler
MappingBeanNameUrlHandlerMapping默认的HandlerAdapter根据mappedHandler选择合适的
HttpRequestHandlerAdapter
SimpleControllerHandlerAdapter
RequestMappingHandlerAdapter
HandlerFunctionAdapter@RequestMapping解析与请求映射
参考流程图： https://www.processon.com/view/link/615ea79e1efad4070b2d6707

执行处理器Handler

1. 执行处理器Handler, 以RequestMappingHandlerAdapter为例
   执行:
   mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

	@Overrideprotected ModelAndView handleInternal(HttpServletRequest request,HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {ModelAndView mav;// 检查当前请求的method是否为支持的method(默认Null,可通过继承AbstractController设置supportedMethods)// 检查当前请求是否必须session  (默认false,可通过继承AbstractController设置requireSession)checkRequest(request);/*** 判断当前是否需要支持在同一个session中只能线性地处理请求* 因为锁是通过 synchronized 是 JVM 进程级，所以在分布式环境下，* 无法达到同步相同 Session 的功能。默认情况下，synchronizeOnSession 为 false*/if (this.synchronizeOnSession) {// 获取当前请求的session对象HttpSession session = request.getSession(false);if (session != null) {// 为当前session生成一个唯一的可以用于锁定的keyObject mutex = WebUtils.getSessionMutex(session);synchronized (mutex) {// 对HandlerMethod进行参数等的适配处理，并调用目标handlermav = invokeHandlerMethod(request, response, handlerMethod);}}else {// 如果当前不存在session，则直接对HandlerMethod进行适配mav = invokeHandlerMethod(request, response, handlerMethod);}}else {// *如果当前不需要对session进行同步处理，则直接对HandlerMethod进行适配mav = invokeHandlerMethod(request, response, handlerMethod);}//判断当前请求头中是否包含Cache-Control请求头，如果不包含，则对当前response进行处理if (!response.containsHeader(HEADER_CACHE_CONTROL)) {// 如果当前SessionAttribute中存在配置的attributes，则为其设置过期时间。// 这里SessionAttribute主要是通过@SessionAttribute注解生成的if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);}else {// 如果当前不存在SessionAttributes，则判断当前是否存在Cache-Control设置，// 如果存在，则按照该设置进行response处理，如果不存在，则设置response中的// Cache的过期时间为-1，即立即失效prepareResponse(response);}}return mav;}

2. 对HandlerMethod进行适配

	@Nullableprotected ModelAndView invokeHandlerMethod(HttpServletRequest request,HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {// 把我们的请求req resp包装成 ServletWebRequestServletWebRequest webRequest = new ServletWebRequest(request, response);try {// 获取容器中全局配置的InitBinder和当前HandlerMethod所对应的Controller中// 配置的InitBinder，用于进行参数的绑定WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);// 获取容器中全局配置的ModelAttribute和当前HandlerMethod所对应的Controller 中配置的ModelAttribute，// 这些配置的方法将会在目标方法调用之前进行调用ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);// 封装handlerMethod，会在调用前解析参数、调用后对返回值进行处理ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);if (this.argumentResolvers != null) {// 让invocableMethod拥有参数解析能力invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);}if (this.returnValueHandlers != null) {// 让invocableMethod拥有返回值处理能力invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);}// 让invocableMethod拥有InitBinder解析能力invocableMethod.setDataBinderFactory(binderFactory);// 设置ParameterNameDiscoverer，该对象将按照一定的规则获取当前参数的名称invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);// ModelAndView处理容器ModelAndViewContainer mavContainer = new ModelAndViewContainer();// 将request的Attribute复制一份到ModelMapmavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));// *调用我们标注了@ModelAttribute的方法,主要是为我们的目标方法预加载modelFactory.initModel(webRequest, mavContainer, invocableMethod);// 重定向的时候，忽略model中的数据 默认falsemavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);// 获取当前的AsyncWebRequest，这里AsyncWebRequest的主要作用是用于判断目标// handler的返回值是否为WebAsyncTask或DeferredResult，如果是这两种中的一种，// 则说明当前请求的处理应该是异步的。所谓的异步，指的是当前请求会将Controller中// 封装的业务逻辑放到一个线程池中进行调用，待该调用有返回结果之后再返回到response中。// 这种处理的优点在于用于请求分发的线程能够解放出来，从而处理更多的请求,提高吞吐。// 只有待目标任务完成之后才会回来将该异步任务的结果返回。AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);asyncWebRequest.setTimeout(this.asyncRequestTimeout);// 封装异步任务的线程池、request、interceptors到WebAsyncManager中WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);asyncManager.setTaskExecutor(this.taskExecutor);asyncManager.setAsyncWebRequest(asyncWebRequest);asyncManager.registerCallableInterceptors(this.callableInterceptors);asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);// 这里就是用于判断当前请求是否有异步任务结果的，如果存在，则对异步任务结果进行封装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);}// *对请求参数进行处理，调用目标HandlerMethod，并且将返回值封装为一个ModelAndView对象invocableMethod.invokeAndHandle(webRequest, mavContainer);if (asyncManager.isConcurrentHandlingStarted()) {return null;}// 对封装的ModelAndView进行处理，主要是判断当前请求是否进行了重定向，如果进行了重定向，// 还会判断是否需要将FlashAttributes封装到新的请求中return getModelAndView(mavContainer, modelFactory, webRequest);}finally {webRequest.requestCompleted();}}

3. 对请求参数进行处理，调用目标HandlerMethod，并且将返回值封装为一个ModelAndView对象 ServletInvocableHandlerMethod
   invocableMethod.invokeAndHandle(webRequest, mavContainer)

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,Object... providedArgs) throws Exception {/*真正的调用我们的目标对象 很重要 很重要*/Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);// 设置相关的返回状态setResponseStatus(webRequest);// 如果请求处理完成，则设置requestHandled属性if (returnValue == null) {if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {disableContentCachingIfNecessary(webRequest);mavContainer.setRequestHandled(true);return;}}// 如果请求失败，但是有错误原因，那么也会设置requestHandled属性else if (StringUtils.hasText(getResponseStatusReason())) {mavContainer.setRequestHandled(true);return;}mavContainer.setRequestHandled(false);Assert.state(this.returnValueHandlers != null, "No return value handlers");try {// 遍历当前容器中所有ReturnValueHandler，判断哪种handler支持当前返回值的处理，// 如果支持，则使用该handler处理该返回值this.returnValueHandlers.handleReturnValue(returnValue, getReturnValueType(returnValue), mavContainer, webRequest);}catch (Exception ex) {if (logger.isTraceEnabled()) {logger.trace(formatErrorForReturnValue(returnValue), ex);}throw ex;}}

4. 真正的调用我们的目标对象 很重要 很重要
   Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);

	@Nullablepublic Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,Object... providedArgs) throws Exception {//*获取我们目标方法入参的值Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);if (logger.isTraceEnabled()) {logger.trace("Arguments: " + Arrays.toString(args));}//真的的调用我们的目标方法return doInvoke(args);}

doInvoke(args) 反射调用