Spring MVC請求處理過程不是兩張流程圖就能講清楚的

來源：blog.csdn.net/Baisitao_/article/details/107471719

/** 文件上傳解析器 */
private?MultipartResolver multipartResolver;

/** 區(qū)域解析器，用于國際化 */
private?LocaleResolver localeResolver;

/** 主題解析器 */
private?ThemeResolver themeResolver;

/** Handler映射信息 */
private?List handlerMappings;

/** Handler適配器*/
private?List handlerAdapters;

/** Handler執(zhí)行異常解析器 */
private?List handlerExceptionResolvers;

/** 請求到視圖的轉(zhuǎn)換器 */
private?RequestToViewNameTranslator viewNameTranslator;

/** SpringMVC允許重定向時攜帶參數(shù)，存在session中，用完就銷毀，所以叫FlashMap */
private?FlashMapManager flashMapManager;

/** 視圖解析器 */
private?List viewResolvers;

@Controller
public?class?IndexController {

????@RequestMapping("/index/home")
????public?String?home(String?id, Student student, @RequestParam("code") String?code) {
????????System.out.println(student.getName());
????????return?"index";
????}

????@ResponseBody
????@RequestMapping("/index/list")
????public?String?list() {
????????return?"success";
????}
}

public?class?Student?{

????private?String name;
????private?Integer gender;

???// getter、setter
}

/**
?* Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
?* for the actual dispatching.
?*/
@Override
protected?void?doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
?logRequest(request);

?// Keep a snapshot of the request attributes in case of an include,
?// to be able to restore the original attributes after the include.
?Map<String, Object> attributesSnapshot = null;
?if?(WebUtils.isIncludeRequest(request)) {
??attributesSnapshot = new?HashMap<>();
??Enumeration attrNames = request.getAttributeNames();
??while?(attrNames.hasMoreElements()) {
???String?attrName = (String) attrNames.nextElement();
???if?(this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
????attributesSnapshot.put(attrName, request.getAttribute(attrName));
???}
??}
?}

?// Make framework objects available to handlers and view objects.
?request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
?request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
?request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
?request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());

?if?(this.flashMapManager != null) {
??FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
??if?(inputFlashMap != null) {
???request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
??}
??request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new?FlashMap());
??request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
?}

?try?{
??// 真正執(zhí)行的方法
??doDispatch(request, response);
?}
?finally?{
??if?(!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
???// Restore the original attribute snapshot, in case of an include.
???if?(attributesSnapshot != null) {
????restoreAttributesAfterInclude(request, attributesSnapshot);
???}
??}
?}
}

/**
?* 實際處理請求的方法
?*/
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?{
???// 校驗是否是文件上傳請求
???processedRequest = checkMultipart(request);
???multipartRequestParsed = (processedRequest != request);

???// Determine handler for the current request.
???// 為當(dāng)前請求找到一個合適的處理器（Handler）
???// 返回值是一個HandlerExecutionChain，也就是處理器執(zhí)行鏈
???mappedHandler = getHandler(processedRequest);
???if?(mappedHandler == null) {
????noHandlerFound(processedRequest, response);
????return;
???}

???// Determine handler adapter for the current request.
???// 根據(jù)HandlerExecutionChain攜帶的Handler找到合適的HandlerAdapter
???HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

???// Process last-modified header, if supported by the handler.
???// 處理GET請求的緩存
???String method = request.getMethod();
???boolean isGet = "GET".equals(method);
???if?(isGet || "HEAD".equals(method)) {
????long?lastModified = ha.getLastModified(request, mappedHandler.getHandler());
????if?(new?ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
?????return;
????}
???}

???// 執(zhí)行攔截器的preHandle方法
???if?(!mappedHandler.applyPreHandle(processedRequest, response)) {
????return;
???}

???// Actually invoke the handler.
???// 利用HandlerAdapter來執(zhí)行Handler里對應(yīng)的處理方法
???mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

???if?(asyncManager.isConcurrentHandlingStarted()) {
????return;
???}

???// 如果沒有設(shè)置視圖，則應(yīng)用默認(rèn)的視圖名
???applyDefaultViewName(processedRequest, mv);
???// 執(zhí)行攔截器的postHandle方法
???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);
??}
??// 根據(jù)ModelAndView對象解析視圖
??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 afterCompletion
???if?(mappedHandler != null) {
????mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
???}
??}
??else?{
???// Clean up any resources used by a multipart request.
???if?(multipartRequestParsed) {
????cleanupMultipart(processedRequest);
???}
??}
?}
}

/**
?* Return the HandlerExecutionChain for this request.
?* 為這個request返回一個HandlerExecutionChain
?*/
@Nullable
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;
}

/**
??* Return the HandlerAdapter for this handler object.
??* @param?handler the handler object to find an adapter for
??* @throws?ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.
??*/
?protected?HandlerAdapter getHandlerAdapter(Object handler)?throws?ServletException {
??if?(this.handlerAdapters != null) {
???for?(HandlerAdapter adapter : this.handlerAdapters) {
????if?(adapter.supports(handler)) {
?????return?adapter;
????}
???}
??}
??throw?new?ServletException("No adapter for handler ["?+ handler +
????"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
?}

/**
?* Handle the result of handler selection and handler invocation, which is
?* either a ModelAndView or an Exception to be resolved to a ModelAndView.
?*/
private?void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
??@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
??@Nullable Exception?exception) throws Exception?{

?boolean errorView = false;

?if?(exception?!= null) {
??if?(exception?instanceof?ModelAndViewDefiningException) {
???logger.debug("ModelAndViewDefiningException encountered", exception);
???mv = ((ModelAndViewDefiningException) exception).getModelAndView();
??}
??else?{
???Object handler = (mappedHandler != null?? mappedHandler.getHandler() : null);
???mv = processHandlerException(request, response, handler, exception);
???errorView = (mv != null);
??}
?}

?// Did the handler return a view to render?
?if?(mv != null?&& !mv.wasCleared()) {
??// 主要調(diào)用該方法渲染視圖
??render(mv, request, response);
??if?(errorView) {
???WebUtils.clearErrorRequestAttributes(request);
??}
?}
?else?{
??if?(logger.isTraceEnabled()) {
???logger.trace("No view rendering, null ModelAndView returned.");
??}
?}

?if?(WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
??// Concurrent handling started during a forward
??return;
?}

?if?(mappedHandler != null) {
??// Exception (if any) is already handled..
??mappedHandler.triggerAfterCompletion(request, response, null);
?}
}

/**
?* Render the given ModelAndView.
?* 
This is the last stage in handling a request. It may involve resolving the view by name.
?* @param?mv the ModelAndView to render
?* @param?request current HTTP servlet request
?* @param?response current HTTP servlet response
?* @throws?ServletException if view is missing or cannot be resolved
?* @throws?Exception if there's a problem rendering the view
?*/
protected?void?render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response)?throws?Exception {
?// Determine locale for request and apply it to the response.
?Locale locale =
???(this.localeResolver != null?? this.localeResolver.resolveLocale(request) : request.getLocale());
?response.setLocale(locale);

?View view;
?String viewName = mv.getViewName();
?if?(viewName != null) {
??// We need to resolve the view name.
??// 根據(jù)給定的視圖名稱，解析獲取View對象
??view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
??if?(view == null) {
???throw?new?ServletException("Could not resolve view with name '"?+ mv.getViewName() +
?????"' in servlet with name '"?+ getServletName() + "'");
??}
?}
?else?{
??// No need to lookup: the ModelAndView object contains the actual View object.
??view = mv.getView();
??if?(view == null) {
???throw?new?ServletException("ModelAndView ["?+ mv + "] neither contains a view name nor a "?+
?????"View object in servlet with name '"?+ getServletName() + "'");
??}
?}

?// Delegate to the View object for rendering.
?if?(logger.isTraceEnabled()) {
??logger.trace("Rendering view ["?+ view + "] ");
?}
?try?{
??if?(mv.getStatus() != null) {
???response.setStatus(mv.getStatus().value());
??}
??view.render(mv.getModelInternal(), request, response);
?}
?catch?(Exception ex) {
??if?(logger.isDebugEnabled()) {
???logger.debug("Error rendering view ["?+ view + "]", ex);
??}
??throw?ex;
?}
}

@Nullable
protected?View resolveViewName(String?viewName, @Nullable?Map<String, Object> model,
??Locale locale, HttpServletRequest request) throws Exception {

?if?(this.viewResolvers != null) {
??for?(ViewResolver viewResolver : this.viewResolvers) {
???View view = viewResolver.resolveViewName(viewName, locale);
???if?(view != null) {
????return?view;
???}
??}
?}
?return?null;
}

<bean?class="org.springframework.web.servlet.view.InternalResourceViewResolver">
?<property?name="prefix"?value="/WEB-INF/views/"?/>
?<property?name="suffix"?value=".html"?/>
bean>

// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

/**
?* This implementation expects the handler to be an {@link HandlerMethod}.
?*/
@Override
@Nullable
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
??throws Exception {

?return?handleInternal(request, response, (HandlerMethod) handler);
}

@Override
protected?ModelAndView handleInternal(HttpServletRequest request,
??HttpServletResponse response, HandlerMethod handlerMethod)?throws?Exception {

?ModelAndView mav;
?// 校驗指定的請求以獲取受支持的方法類型（GET、POST等）和所需的session
?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 necessary
???mav = invokeHandlerMethod(request, response, handlerMethod);
??}
?}
?else?{
??// No synchronization on session demanded at all...
??// 真正執(zhí)行handler的方法
??mav = invokeHandlerMethod(request, response, handlerMethod);
?}

?if?(!response.containsHeader(HEADER_CACHE_CONTROL)) {
??if?(getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
???applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
??}
??else?{
???prepareResponse(response);
??}
?}

?return?mav;
}

/**
?* Invoke the {@link?RequestMapping} handler method preparing a {@link?ModelAndView}
?* if view resolution is required.
?* 執(zhí)行@RequestMapping標(biāo)注的handler方法，如果需要解析視圖就準(zhǔn)備一個ModelAndView
?*/
@Nullable
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);

??// HandlerMethod接口封裝執(zhí)行方法的信息，提供對方法參數(shù)，方法返回值，方法注釋等的便捷訪問。
??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可以看做ModelAndView的上下文容器，關(guān)聯(lián)著Model和View的信息
??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);
??}

??// 真正執(zhí)行Handler的方法
??invocableMethod.invokeAndHandle(webRequest, mavContainer);
??if?(asyncManager.isConcurrentHandlingStarted()) {
???return?null;
??}

??// 獲取ModelAndeView對象
??return?getModelAndView(mavContainer, modelFactory, webRequest);
?}
?finally?{
??webRequest.requestCompleted();
?}
}

/**
?* Invoke the method and handle the return value through one of the
?* configured {@link?HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers}.
?* @param?webRequest the current request
?* @param?mavContainer the ModelAndViewContainer for this request
?* @param?providedArgs "given" arguments matched by type (not resolved)
?*/
public?void?invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
??Object... providedArgs)?throws?Exception {

?// 執(zhí)行handler的方法
?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?{
??this.returnValueHandlers.handleReturnValue(
????returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
?}
?catch?(Exception ex) {
??if?(logger.isTraceEnabled()) {
???logger.trace(formatErrorForReturnValue(returnValue), ex);
??}
??throw?ex;
?}
}

/**
?* Invoke the method after resolving its argument values in the context of the given request.
?* 
Argument values are commonly resolved through
?* {@link?HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}.
?* The {@code?providedArgs} parameter however may supply argument values to be used directly,
?* i.e. without argument resolution. Examples of provided argument values include a
?* {@link?WebDataBinder}, a {@link?SessionStatus}, or a thrown exception instance.
?* Provided argument values are checked before argument resolvers.
?* 
Delegates to {@link?#getMethodArgumentValues} and calls {@link?#doInvoke} with the
?* resolved arguments.
?* @param?request the current request
?* @param?mavContainer the ModelAndViewContainer for this request
?* @param?providedArgs "given" arguments matched by type, not resolved
?* @return?the raw value returned by the invoked method
?* @throws?Exception raised if no suitable argument resolver can be found,
?* or if the method raised an exception
?* @see?#getMethodArgumentValues
?* @see?#doInvoke
?*/
@Nullable
public?Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
??Object... providedArgs) throws Exception?{

?// 獲取參數(shù)
?Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
?if?(logger.isTraceEnabled()) {
??logger.trace("Arguments: "?+ Arrays.toString(args));
?}
?// 執(zhí)行
?return?doInvoke(args);
}

/**
?* Get the method argument values for the current request, checking the provided
?* argument values and falling back to the configured argument resolvers.
?* 
The resulting array will be passed into {@link #doInvoke}.
?* @since 5.1.2
?*/
protected?Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable?ModelAndViewContainer mavContainer,
??Object... providedArgs) throws Exception {

?// 獲取方法上所有的參數(shù)
?MethodParameter[] parameters = getMethodParameters();
?if?(ObjectUtils.isEmpty(parameters)) {
??return?EMPTY_ARGS;
?}

?Object[] args = new?Object[parameters.length];
?for?(int i = 0; i < parameters.length; i++) {
??MethodParameter parameter = parameters[i];
??parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
??args[i] = findProvidedArgument(parameter, providedArgs);
??if?(args[i] != null) {
???continue;
??}
??if?(!this.resolvers.supportsParameter(parameter)) {
???throw?new?IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
??}
??try?{
???
???args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
??}
??catch?(Exception ex) {
???// Leave stack trace for later, exception may actually be resolved and handled...
???if?(logger.isDebugEnabled()) {
????String?exMsg = ex.getMessage();
????if?(exMsg != null?&& !exMsg.contains(parameter.getExecutable().toGenericString())) {
?????logger.debug(formatArgumentError(parameter, exMsg));
????}
???}
???throw?ex;
??}
?}
?return?args;
}

/**
?* Iterate over registered
?* {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}
?* and invoke the one that supports it.
?* @throws IllegalArgumentException if no suitable argument resolver is found
?*/
@Override
@Nullable
public?Object?resolveArgument(MethodParameter parameter, @Nullable?ModelAndViewContainer mavContainer,
??NativeWebRequest webRequest, @Nullable?WebDataBinderFactory binderFactory) throws Exception {

?// 獲取合適的參數(shù)解析器
?HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
?if?(resolver == null) {
??throw?new?IllegalArgumentException("Unsupported parameter type ["?+
????parameter.getParameterType().getName() + "]. supportsParameter should be called first.");
?}
?// 執(zhí)行參數(shù)綁定
?return?resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
}

/**
?* Find a registered {@link HandlerMethodArgumentResolver} that supports
?* the given method parameter.
?*/
@Nullable
private?HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
?HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
?if?(result == null) {
??for?(HandlerMethodArgumentResolver resolver : this.argumentResolvers) {
???if?(resolver.supportsParameter(parameter)) {
????result = resolver;
????this.argumentResolverCache.put(parameter, result);
????break;
???}
??}
?}
?return?result;
}

/**
?* Resolve the argument from the model or if not found instantiate it with
?* its default if it is available. The model attribute is then populated
?* with request values via data binding and optionally validated
?* if {@code @java.validation.Valid} is present on the argument.
?* @throws BindException if data binding and validation result in an error
?* and the next method parameter is not of type {@link Errors}
?* @throws Exception if WebDataBinder initialization fails
?*/
@Override
@Nullable
public?final Object?resolveArgument(MethodParameter parameter, @Nullable?ModelAndViewContainer mavContainer,
??NativeWebRequest webRequest, @Nullable?WebDataBinderFactory binderFactory) throws Exception {

?Assert.state(mavContainer != null, "ModelAttributeMethodProcessor requires ModelAndViewContainer");
?Assert.state(binderFactory != null, "ModelAttributeMethodProcessor requires WebDataBinderFactory");

?// 獲取參數(shù)名
?String?name = ModelFactory.getNameForParameter(parameter);
?// 獲取參數(shù)上的ModelAttribute注解
?ModelAttribute ann = parameter.getParameterAnnotation(ModelAttribute.class);
?if?(ann != null) {
??mavContainer.setBinding(name, ann.binding());
?}

?Object?attribute = null;
?BindingResult bindingResult = null;

?if?(mavContainer.containsAttribute(name)) {
??attribute = mavContainer.getModel().get(name);
?}
?else?{
??// Create attribute instance
??try?{
???// 創(chuàng)建參數(shù)類型的實例（未注入值），底層就是通過反射調(diào)用構(gòu)造方法
???attribute = createAttribute(name, parameter, binderFactory, webRequest);
??}
??catch?(BindException ex) {
???if?(isBindExceptionRequired(parameter)) {
????// No BindingResult parameter -> fail with BindException
????throw?ex;
???}
???// Otherwise, expose null/empty value and associated BindingResult
???if?(parameter.getParameterType() == Optional.class) {
????attribute = Optional.empty();
???}
???bindingResult = ex.getBindingResult();
??}
?}

?if?(bindingResult == null) {
??// Bean property binding and validation;
??// skipped in case of binding failure on construction.
??WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);
??if?(binder.getTarget() != null) {
???if?(!mavContainer.isBindingDisabled(name)) {
????// 真正執(zhí)行綁定（值注入）的方法
????bindRequestParameters(binder, webRequest);
???}
???validateIfApplicable(binder, parameter);
???if?(binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
????throw?new?BindException(binder.getBindingResult());
???}
??}
??// Value type adaptation, also covering java.util.Optional
??if?(!parameter.getParameterType().isInstance(attribute)) {
???attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
??}
??bindingResult = binder.getBindingResult();
?}

?// Add resolved attribute and BindingResult at the end of the model
?Map<String, Object> bindingResultModel = bindingResult.getModel();
?mavContainer.removeAttributes(bindingResultModel);
?mavContainer.addAllAttributes(bindingResultModel);

?return?attribute;
}

/**
?* This implementation downcasts {@link?WebDataBinder} to
?* {@link?ServletRequestDataBinder} before binding.
?* @see?ServletRequestDataBinderFactory
?*/
@Override
protected?void?bindRequestParameters(WebDataBinder binder, NativeWebRequest request)?{
?ServletRequest servletRequest = request.getNativeRequest(ServletRequest.class);
?Assert.state(servletRequest != null, "No ServletRequest");
?ServletRequestDataBinder servletBinder = (ServletRequestDataBinder) binder;
?// 執(zhí)行綁定的方法
?servletBinder.bind(servletRequest);
}

public?void?bind(ServletRequest request) {
?// 獲取所有參數(shù)的鍵值對
?MutablePropertyValues mpvs = new?ServletRequestParameterPropertyValues(request);
?// 處理文件上傳請求
?MultipartRequest multipartRequest = WebUtils.getNativeRequest(request, MultipartRequest.class);
?if?(multipartRequest != null) {
??bindMultipart(multipartRequest.getMultiFileMap(), mpvs);
?}
?// 把url中攜帶的參數(shù)也加入到MutablePropertyValues
?addBindValues(mpvs, request);
?// 執(zhí)行綁定（注入值）
?doBind(mpvs);
}

/**
?* Invoke the method and handle the return value through one of the
?* configured {@link?HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers}.
?* @param?webRequest the current request
?* @param?mavContainer the ModelAndViewContainer for this request
?* @param?providedArgs "given" arguments matched by type (not resolved)
?*/
public?void?invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
??Object... providedArgs)?throws?Exception {

?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?{
??// 真正處理不同類型返回值的方法
??this.returnValueHandlers.handleReturnValue(
????returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
?}
?catch?(Exception ex) {
??if?(logger.isTraceEnabled()) {
???logger.trace(formatErrorForReturnValue(returnValue), ex);
??}
??throw?ex;
?}
}

/**
?* Iterate over registered {@link?HandlerMethodReturnValueHandler HandlerMethodReturnValueHandlers} and invoke the one that supports it.
?* @throws?IllegalStateException if no suitable {@link?HandlerMethodReturnValueHandler} is found.
?*/
@Override
public?void?handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
??ModelAndViewContainer mavContainer, NativeWebRequest webRequest)?throws?Exception {

?// 根據(jù)返回值個返回值類型選取合適的HandlerMethodReturnValueHandler
?HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
?if?(handler == null) {
??throw?new?IllegalArgumentException("Unknown return value type: "?+ returnType.getParameterType().getName());
?}
?// 真正的處理返回值
?handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
}

@Nullable
private?HandlerMethodReturnValueHandler selectHandler(@Nullable?Object?value, MethodParameter returnType) {
?boolean?isAsyncValue = isAsyncReturnValue(value, returnType);
?for?(HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
??if?(isAsyncValue && !(handler instanceof?AsyncHandlerMethodReturnValueHandler)) {
???continue;
??}
??if?(handler.supportsReturnType(returnType)) {
???return?handler;
??}
?}
?return?null;
}

@Override
public?void?handleReturnValue(@Nullable?Object?returnValue, MethodParameter returnType,
??ModelAndViewContainer mavContainer, NativeWebRequest webRequest)
??throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

?// 設(shè)置該請求是否已在處理程序中完全處理，例如@ResponseBody方法不需要視圖解析器，此處就可以設(shè)置為true。
?// 當(dāng)控制器方法聲明類型為ServletResponse或OutputStream的參數(shù)時，也可以設(shè)置此標(biāo)志為true。
?// 這個屬性設(shè)置成true之后，上層getModelAndView獲取ModelAndView時會返回Null，因為不需要視圖。
?// 默認(rèn)值為false
?mavContainer.setRequestHandled(true);
?ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
?ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);

?// Try even with null return value. ResponseBodyAdvice could get involved.
?// 底層就是利用java.io.OutputStreamWriter類把返回值寫到網(wǎng)絡(luò)IO
?writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);
}