SpringBoot版本2.2.4.RELEASE。

【1】SpringBoot接收到請求

① springboot接收到一個請求返回json格式的列表，方法參數(shù)為JSONObject 格式，使用了注解@RequestBody

為什么這里要說明返回格式、方法參數(shù)、參數(shù)注解？因為方法參數(shù)與參數(shù)注解會影響你使用不同的參數(shù)解析器與后置處理器！通常使用WebDataBinder進(jìn)行參數(shù)數(shù)據(jù)綁定結(jié)果也不同。

將要調(diào)用的目標(biāo)方法如下：

@ApiOperation(value='分頁查詢') @RequestMapping(value = '/listPage',method = RequestMethod.POST) @ResponseBody public ResponseBean listPage(@RequestBody JSONObject params){ Integer pageNum = params.getInteger('pageNum'); Integer pageSize = params.getInteger('pageSize'); String vagueParam = params.getString('vagueParam'); IPage<TbSysGoodsCategory> indexPage = new Page<>(pageNum, pageSize); QueryWrapper<TbSysGoodsCategory> queryWrapper = new QueryWrapper<>(); if (!StringUtils.isEmpty(vagueParam)){ queryWrapper.like('name',vagueParam).or().like('code',vagueParam); } //排序 queryWrapper.orderByDesc('id'); indexPage = tbSysGoodsCategoryService.page(indexPage,queryWrapper); return new ResponseBean<>(true, indexPage, CommonEnum.SUCCESS_OPTION); }

如下所示，首先進(jìn)入DispatcherServlet使用RequestMappingHandlerAdapter進(jìn)行處理。

而RequestMappingHandlerAdapter (extends AbstractHandlerMethodAdapter)會調(diào)用父類AbstractHandlerMethodAdapter的handle方法進(jìn)行處理。

AbstractHandlerMethodAdapter.handle方法源碼如下：

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

可以看到RequestMappingHandlerAdapter還實現(xiàn)了InitializingBean接口，該接口只有一個抽象方法afterPropertiesSet用于在BeanFactory設(shè)置完bean屬性后執(zhí)行，具體可參考博文：Spring - bean的初始化和銷毀幾種實現(xiàn)方式詳解

② RequestMappingHandlerAdapter.handleInternal

這里首先在this.checkRequest(request)對請求進(jìn)行了檢測，HttpRequestMethodNotSupportedException異常就是這里拋出的。

//1.檢測請求方法是否支持；//2.檢測是否需要session但是沒有獲取到protected final void checkRequest(HttpServletRequest request) throws ServletException {// Check whether we should support the request method.String method = request.getMethod();if (this.supportedMethods != null && !this.supportedMethods.contains(method)) {throw new HttpRequestMethodNotSupportedException(method, this.supportedMethods);}// Check whether a session is required.if (this.requireSession && request.getSession(false) == null) {throw new HttpSessionRequiredException('Pre-existing session required but none found');}}

其他沒有什么需要特殊說明的，然后直接調(diào)用了invokeHandlerMethod方法進(jìn)行實際業(yè)務(wù)處理。

【2】RequestMappingHandlerAdapter.invokeHandlerMethod核心處理

RequestMappingHandlerAdapter.invokeHandlerMethod

這個方法十分重要，是請求處理流程中的核心方法。這個方法會根據(jù)handlerMethod獲取一個ServletInvocableHandlerMethod 并對其進(jìn)行各種屬性設(shè)置然后調(diào)用其invokeAndHandle方法進(jìn)行處理。

@Nullable protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { // 對應(yīng) 2 ServletWebRequest webRequest = new ServletWebRequest(request, response); Object result; try {// 對應(yīng) 3 WebDataBinderFactory binderFactory = this.getDataBinderFactory(handlerMethod); // 對應(yīng) 4 ModelFactory modelFactory = this.getModelFactory(handlerMethod, binderFactory); // 對應(yīng) 5 ServletInvocableHandlerMethod invocableMethod = this.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); // 對應(yīng) 6 ModelAndViewContainer mavContainer = new ModelAndViewContainer(); mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request)); modelFactory.initModel(webRequest, mavContainer, invocableMethod); mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);//對應(yīng) 7 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()) {result = asyncManager.getConcurrentResult();mavContainer = (ModelAndViewContainer)asyncManager.getConcurrentResultContext()[0];asyncManager.clearConcurrentResult();LogFormatUtils.traceDebug(this.logger, (traceOn) -> { String formatted = LogFormatUtils.formatValue(result, !traceOn); return 'Resume with async result [' + formatted + ']';});invocableMethod = invocableMethod.wrapConcurrentResult(result); }//這里會跳到【3】ServletInvocableHandlerMethod.invokeAndHandle invocableMethod.invokeAndHandle(webRequest, mavContainer, new Object[0]); if (!asyncManager.isConcurrentHandlingStarted()) {//這里會跳到【4】RequestMappingHandlerAdapter.getModelAndViewModelAndView var15 = this.getModelAndView(mavContainer, modelFactory, webRequest);return var15; } result = null; } finally { //這里會跳到【5】ServletWebRequest.requestCompleted webRequest.requestCompleted(); } return (ModelAndView)result; }

① 此時的handlerMethod是什么？

如下圖所示，handlermethod里面有bean、創(chuàng)建bean的工廠、bean的類型、原始方法method、橋接方法bridgedMethod以及參數(shù)對象parameters等關(guān)鍵屬性。

其他都容易理解，那么什么是bridgedMethod?（后續(xù)單獨分析）

② 此時的ServletWebRequest webRequest是什么？

這個倒是很簡單，如下圖所示：

③ 此時的WebDataBinderFactory binderFactory

WebDataBinderFactory binderFactory = this.getDataBinderFactory(handlerMethod);

RequestMappingHandlerAdapter.getDataBinderFactory源碼如下：

private WebDataBinderFactory getDataBinderFactory(HandlerMethod handlerMethod) throws Exception {//獲取handlerType Class<?> handlerType = handlerMethod.getBeanType();//根據(jù)handlerType 從initBinderCache獲取到@InitBinder注解的方法Set<Method> methods = this.initBinderCache.get(handlerType);//如果initBinderCache中沒有，就從handlerType查找@InitBinder注解的方法if (methods == null) {methods = MethodIntrospector.selectMethods(handlerType, INIT_BINDER_METHODS);this.initBinderCache.put(handlerType, methods);}List<InvocableHandlerMethod> initBinderMethods = new ArrayList<>();//遍歷controllerAdviceBean的方法列表，從適合handlerType中拿到其方法列表//然后封裝為一個個InvocableHandlerMethod放到initBinderMethods中// Global methods firstthis.initBinderAdviceCache.forEach((controllerAdviceBean, methodSet) -> {if (controllerAdviceBean.isApplicableToBeanType(handlerType)) {Object bean = controllerAdviceBean.resolveBean();for (Method method : methodSet) {initBinderMethods.add(createInitBinderMethod(bean, method));}}});for (Method method : methods) {Object bean = handlerMethod.getBean();initBinderMethods.add(createInitBinderMethod(bean, method));}return createDataBinderFactory(initBinderMethods);}

首先Class<?> handlerType = handlerMethod.getBeanType();通過handlerMethod獲取到handlerTYPE，handlerTYPE聲明了當(dāng)前完整類路徑以及類上面的注解。其值如下：

然后Set<Method> methods = this.initBinderCache.get(handlerType);嘗試先從initBinderCache這個ConcurrentHashMap中獲取當(dāng)前類的使用了InitBinder注解的方法列表。如果methods為空，則從handlerType中獲取使用了@InitBinder注解的方法，然后放到initBinderCache中，對應(yīng)代碼this.initBinderCache.put(handlerType, methods);

這個很關(guān)鍵。SpringBoot請求處理流程中最重要的一步就是數(shù)據(jù)綁定，即將參數(shù)寫到目標(biāo)對象上面。那么這里就涉及到參數(shù)校驗、數(shù)據(jù)格式轉(zhuǎn)換、綁定結(jié)果對象、錯誤對象等。

最后return createDataBinderFactory(initBinderMethods);其會拿到WebBindingInitializer創(chuàng)建數(shù)據(jù)綁定工廠，。

protected InitBinderDataBinderFactory createDataBinderFactory(List<InvocableHandlerMethod> binderMethods)throws Exception {return new ServletRequestDataBinderFactory(binderMethods, getWebBindingInitializer());}

DataBinderFactory其屬性ConfigurableWebBindingInitializer對象提供了基礎(chǔ)功能，該對象中WebConversionService中轉(zhuǎn)換器實例如下：

④ 根據(jù)handlerMethod和binderFactory獲取到ModelFactory modelFactory

ModelFactory modelFactory = this.getModelFactory(handlerMethod, binderFactory);

RequestMappingHandlerAdapter.getModelFactory方法源碼如下：

private ModelFactory getModelFactory(HandlerMethod handlerMethod, WebDataBinderFactory binderFactory) {//獲取當(dāng)前handlerMethod對應(yīng)的handlerType的SessionAttributesHandler //--如果沒有就創(chuàng)建一個new SessionAttributesHandler(handlerType, this.sessionAttributeStore)//參考④-①SessionAttributesHandler sessionAttrHandler = getSessionAttributesHandler(handlerMethod);//獲取handlerType Class<?> handlerType = handlerMethod.getBeanType();//獲取添加了@ModelAttribute注解的方法Set<Method> methods = this.modelAttributeCache.get(handlerType);if (methods == null) {methods = MethodIntrospector.selectMethods(handlerType, MODEL_ATTRIBUTE_METHODS);this.modelAttributeCache.put(handlerType, methods);}List<InvocableHandlerMethod> attrMethods = new ArrayList<>();//從controllerAdviceBean中獲取適合當(dāng)前handlerType的method，//并封裝為一個個InvocableHandlerMethod然后添加到attrMethods// Global methods firstthis.modelAttributeAdviceCache.forEach((controllerAdviceBean, methodSet) -> {if (controllerAdviceBean.isApplicableToBeanType(handlerType)) {Object bean = controllerAdviceBean.resolveBean();for (Method method : methodSet) {attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));}}});//遍歷methods并封裝為一個個InvocableHandlerMethod然后添加到attrMethodsfor (Method method : methods) {Object bean = handlerMethod.getBean();attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));}//根據(jù)attrMethods, binderFactory, sessionAttrHandler創(chuàng)建一個ModelFactory對象return new ModelFactory(attrMethods, binderFactory, sessionAttrHandler);}

可以看到modelFactory主要屬性modelMethods、dataBindFactory和sessionAttributeHandler都是為參數(shù)綁定數(shù)據(jù)服務(wù)的。

④-① RequestMappingHandlerAdapter.getSessionAttributesHandler獲取給定類型的SessionAttributesHandler

方法源碼如下：

private ModelFactory getModelFactory(HandlerMethod handlerMethod, WebDataBinderFactory binderFactory) {//獲取當(dāng)前handlerMethod對應(yīng)的handlerType的SessionAttributesHandler //--如果沒有就創(chuàng)建一個new SessionAttributesHandler(handlerType, this.sessionAttributeStore)//參考④-①SessionAttributesHandler sessionAttrHandler = getSessionAttributesHandler(handlerMethod);//獲取handlerType Class<?> handlerType = handlerMethod.getBeanType();//獲取添加了@ModelAttribute注解的方法Set<Method> methods = this.modelAttributeCache.get(handlerType);if (methods == null) {methods = MethodIntrospector.selectMethods(handlerType, MODEL_ATTRIBUTE_METHODS);this.modelAttributeCache.put(handlerType, methods);}List<InvocableHandlerMethod> attrMethods = new ArrayList<>();//從controllerAdviceBean中獲取適合當(dāng)前handlerType的method，//并封裝為一個個InvocableHandlerMethod然后添加到attrMethods// Global methods firstthis.modelAttributeAdviceCache.forEach((controllerAdviceBean, methodSet) -> {if (controllerAdviceBean.isApplicableToBeanType(handlerType)) {Object bean = controllerAdviceBean.resolveBean();for (Method method : methodSet) {attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));}}});//遍歷methods并封裝為一個個InvocableHandlerMethod然后添加到attrMethodsfor (Method method : methods) {Object bean = handlerMethod.getBean();attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));}//根據(jù)attrMethods, binderFactory, sessionAttrHandler創(chuàng)建一個ModelFactory對象return new ModelFactory(attrMethods, binderFactory, sessionAttrHandler);}

④-①-①SessionAttributesHandler.SessionAttributesHandler

構(gòu)造方法源碼如下：

public SessionAttributesHandler(Class<?> handlerType, SessionAttributeStore sessionAttributeStore) {Assert.notNull(sessionAttributeStore, 'SessionAttributeStore may not be null');this.sessionAttributeStore = sessionAttributeStore;//嘗試從handlerType獲取@SessionAttributes注解SessionAttributes ann = AnnotatedElementUtils.findMergedAnnotation(handlerType, SessionAttributes.class);if (ann != null) {//注解的name屬性值放入attributeNames中Collections.addAll(this.attributeNames, ann.names());//注解的type屬性值放入attributeTypesCollections.addAll(this.attributeTypes, ann.types());}//把所有的attributeNames放入knownAttributeNames//在初始化model方法initModel將會使用這些數(shù)據(jù)this.knownAttributeNames.addAll(this.attributeNames);}

也就是經(jīng)過③④兩步，創(chuàng)建binderFactory、modelFactory后就會拿到匹配當(dāng)前handlerMethod的那些@InitBinder、@ModelAttribute的方法(HandlerMethod對象)以及SessionAttributesHandler ！這三個東西能做什么？當(dāng)你為目標(biāo)方法參數(shù)綁定數(shù)據(jù)的時候就會用到！

⑤ 創(chuàng)建核心處理對象ServletInvocableHandlerMethod invocableMethod并為其屬性賦值

ServletInvocableHandlerMethod invocableMethod = this.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);

ServletInvocableHandlerMethod invocableMethod = this.createInvocableHandlerMethod(handlerMethod);創(chuàng)建ServletInvocableHandlerMethod實例：

protected HandlerMethod(HandlerMethod handlerMethod) {Assert.notNull(handlerMethod, 'HandlerMethod is required');this.bean = handlerMethod.bean;this.beanFactory = handlerMethod.beanFactory;this.beanType = handlerMethod.beanType;this.method = handlerMethod.method;this.bridgedMethod = handlerMethod.bridgedMethod;this.parameters = handlerMethod.parameters;this.responseStatus = handlerMethod.responseStatus;this.responseStatusReason = handlerMethod.responseStatusReason;this.description = handlerMethod.description;this.resolvedFromHandlerMethod = handlerMethod.resolvedFromHandlerMethod;}

invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);為invocableMethod設(shè)置參數(shù)解析器組合對象-HandlerMethodArgumentResolverComposite。其有List<HandlerMethodArgumentResolver> argumentResolvers和Map<MethodParameter, HandlerMethodArgumentResolver> argumentResolverCache兩個重要屬性。其中具體解析器值列表如下：

我想你現(xiàn)在應(yīng)該知道為什么方法參數(shù)使用@RequestBody就可以進(jìn)行參數(shù)綁定了吧！

繼續(xù)看returnValueHandlers，也就是返回結(jié)果處理器。其中returnValueHandlers是HandlerMethodReturnValueHandlerComposite實例，就像HandlermethodArgumentResolverComposite一樣，它包含了所有HandlerMethodReturnValueHandler的列表，并在Spring啟動時完成注冊。其值列表如下：

ok，我們的主題來了。就是這個RequestResponseBodyMethodProcessor后置處理器對@ResponseBody注解進(jìn)行的處理！

繼續(xù)往下走，invocableMethod.setDataBinderFactory(binderFactory);給invocableMethod設(shè)置了DataBinderFactory。這個同上都是為數(shù)據(jù)參數(shù)綁定服務(wù)，繼續(xù)往下看invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);parameterNameDiscoverer這里值列表如下：

⑥ 創(chuàng)建mavContainer進(jìn)行數(shù)據(jù)的初步處理

//創(chuàng)建ModelAndViewContainer 實例對象ModelAndViewContainer mavContainer = new ModelAndViewContainer();//從請求中獲取InputFlashMap并把其數(shù)據(jù)放入defaultModel中，flashmap的作用是在redirect中傳遞參數(shù)mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));//調(diào)用modelFactory對model進(jìn)行初始化modelFactory.initModel(webRequest, mavContainer, invocableMethod);//重定向時忽略默認(rèn)ModelmavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

首先看下ModelAndViewContainer，其核心有三個屬性view-視圖對象，defaultModel-默認(rèn)的數(shù)據(jù)存放地方以及redirectModel-重定向時數(shù)據(jù)存放地方。

modelFactory.initModel(webRequest, mavContainer, invocableMethod);，這里對model做了處理。也可以說是對目標(biāo)方法實際調(diào)用前對數(shù)據(jù)做的最后一次處理：

public void initModel(NativeWebRequest request, ModelAndViewContainer container, HandlerMethod handlerMethod)throws Exception {//獲取會話屬性鍵值對Map<String, ?> sessionAttributes = this.sessionAttributesHandler.retrieveAttributes(request);//對model中屬性-值進(jìn)行合并處理：稱之為補(bǔ)缺更合適//如果model中不存在，則放入---這個很重要container.mergeAttributes(sessionAttributes);//調(diào)用標(biāo)注了@ModelAttribute注解的方法invokeModelAttributeMethods(request, container);//如果handlerMethod的方法參數(shù)標(biāo)注了@ModelAttribute注解并且在sessionAttributetes存在/或類型匹配，則對其進(jìn)行遍歷//嘗試獲取值，如果獲取不到值就會拋出異常；如果獲取到值就會放到model-defaultModel中for (String name : findSessionAttributeArguments(handlerMethod)) {if (!container.containsAttribute(name)) {Object value = this.sessionAttributesHandler.retrieveAttribute(request, name);if (value == null) {throw new HttpSessionRequiredException('Expected session attribute ’' + name + '’', name);}container.addAttribute(name, value);}}}

Map<String, ?> sessionAttributes = this.sessionAttributesHandler.retrieveAttributes(request);獲取會話屬性鍵值對，方法源碼如下：

public Map<String, Object> retrieveAttributes(WebRequest request) {Map<String, Object> attributes = new HashMap<>();//遍歷通過@SessionAttributes注解獲取的namefor (String name : this.knownAttributeNames) {//從session中獲取name對應(yīng)的值Object value = this.sessionAttributeStore.retrieveAttribute(request, name);if (value != null) {//如果值存在，則放入attributesattributes.put(name, value);}}return attributes;}

container.mergeAttributes(sessionAttributes);關(guān)于ModelMap.mergeAttributes合并屬性方法源碼如下：

#也就是說遍歷sessionAttributes ，如果model中不存在，就放入。如果存在，就跳過！注意，不會進(jìn)行值覆蓋 public ModelMap mergeAttributes(@Nullable Map<String, ?> attributes) { if (attributes != null) { attributes.forEach((key, value) -> {if (!this.containsKey(key)) { this.put(key, value);//this這里值的是modelMap，也就是defaultModel} }); } return this; }

這里 invokeModelAttributeMethods(request, container);調(diào)用了@ModelAttribute注解的方法，該方法通常會對model中的值進(jìn)行更新。從另外一個方面來說呢，類里面的@ModelAttribute方法會在目標(biāo)方法調(diào)用前逐個進(jìn)行調(diào)用！，方法源碼如下：

private void invokeModelAttributeMethods(NativeWebRequest request, ModelAndViewContainer container)throws Exception {//循環(huán)調(diào)用modelMethod while (!this.modelMethods.isEmpty()) {InvocableHandlerMethod modelMethod = getNextModelMethod(container).getHandlerMethod();ModelAttribute ann = modelMethod.getMethodAnnotation(ModelAttribute.class);Assert.state(ann != null, 'No ModelAttribute annotation');if (container.containsAttribute(ann.name())) {if (!ann.binding()) {container.setBindingDisabled(ann.name());}continue;}//反射調(diào)用方法并獲取返回值Object returnValue = modelMethod.invokeForRequest(request, container);//如果返回值不為空，就放入model-(returnValueName, returnValue)if (!modelMethod.isVoid()){String returnValueName = getNameForReturnValue(returnValue, modelMethod.getReturnType());if (!ann.binding()) {container.setBindingDisabled(returnValueName);}if (!container.containsAttribute(returnValueName)) {container.addAttribute(returnValueName, returnValue);}}}}

關(guān)于findSessionAttributeArguments方法源碼如下：

//從方法參數(shù)中找到在(@SessionAttributes注解的屬性/參數(shù))中存在的或者類型匹配 // 且方法參數(shù)上標(biāo)注了@ModelAttribute注解的屬性名集合private List<String> findSessionAttributeArguments(HandlerMethod handlerMethod) {List<String> result = new ArrayList<>();for (MethodParameter parameter : handlerMethod.getMethodParameters()) {if (parameter.hasParameterAnnotation(ModelAttribute.class)) {String name = getNameForParameter(parameter);Class<?> paramType = parameter.getParameterType();if (this.sessionAttributesHandler.isHandlerSessionAttribute(name, paramType)) {result.add(name);}}}return result;}

⑦ 異步請求

這一塊先不用管，后續(xù)分析

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);}

接下來調(diào)用invocableMethod.invokeAndHandle(webRequest, mavContainer);就到了ServletInvocableHandlerMethod.invokeAndHandle。

【3】調(diào)用目標(biāo)方法并對返回值進(jìn)行處理ServletInvocableHandlerMethod.invokeAndHandle

其類繼承示意圖如下：

ServletInvocableHandlerMethod.invokeAndHandle方法源碼如下：

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,Object... providedArgs) throws Exception {//調(diào)用目標(biāo)方法并獲取返回值，這里對應(yīng) 【3.1】 InvocableHandlerMethod.invokeForRequest調(diào)用目標(biāo)方法Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);//設(shè)置響應(yīng)狀態(tài)setResponseStatus(webRequest);//如果返回值為null，則將mavContainer.RequestHandled設(shè)置為true，表示已經(jīng)處理不需要視圖解析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;}//將mavContainer.RequestHandled設(shè)置為falsemavContainer.setRequestHandled(false);Assert.state(this.returnValueHandlers != null, 'No return value handlers');//返回值進(jìn)行處理 ，這里對應(yīng)【3.2】try {this.returnValueHandlers.handleReturnValue(returnValue, getReturnValueType(returnValue), mavContainer, webRequest);}catch (Exception ex) {if (logger.isTraceEnabled()) {logger.trace(formatErrorForReturnValue(returnValue), ex);}throw ex;}}

關(guān)于mavContainer.setRequestHandled(false);源碼如下：

public void setRequestHandled(boolean requestHandled) {this.requestHandled = requestHandled;}

檢驗請求添加了@ResponseBody注解的方法是否已經(jīng)處理完，如果處理完則視圖解析不再需要。當(dāng)方法參數(shù)有ServletResponse或者OutputStream類型時，同樣可以設(shè)置這個標(biāo)識。requestHandled 默認(rèn)值為false。

【3.1】 InvocableHandlerMethod.invokeForRequest調(diào)用目標(biāo)方法

其方法源碼如下所示，結(jié)構(gòu)很清晰：獲取方法參數(shù)值然后調(diào)用目標(biāo)方法：

public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,Object... providedArgs) throws Exception {//解析參數(shù)--這里對應(yīng) 1Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);if (logger.isTraceEnabled()) {logger.trace('Arguments: ' + Arrays.toString(args));}//根據(jù)上面得到的參數(shù)值調(diào)用目標(biāo)方法 這里對應(yīng) 2 return doInvoke(args);}

① 解析參數(shù)getMethodArgumentValues

protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,Object... providedArgs) throws Exception {//獲取到方法的參數(shù)對象 MethodParameter[]數(shù)組MethodParameter[] parameters = getMethodParameters();//如果為空，返回空參數(shù)組if (ObjectUtils.isEmpty(parameters)) {return EMPTY_ARGS;}Object[] args = new Object[parameters.length];//遍歷MethodParameter[] parameters，對每一個方法參數(shù)對象獲取到具體參數(shù)并解析得到參數(shù)值for (int i = 0; i < parameters.length; i++) {MethodParameter parameter = parameters[i];//綁定參數(shù)名稱發(fā)現(xiàn)器parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);//從providedArgs中嘗試獲取到參數(shù)名args[i] = findProvidedArgument(parameter, providedArgs);if (args[i] != null) {continue;}//如果方法參數(shù)解析器不支持parameter，則拋出異常if (!this.resolvers.supportsParameter(parameter)) {throw new IllegalStateException(formatArgumentError(parameter, 'No suitable resolver'));}try {//使用參數(shù)解析器解析參數(shù)獲取到值，下面會重點分析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;}

MethodParameter[] parameters = getMethodParameters();這里獲取的 MethodParameter[] parameters如下圖所示：

參數(shù)解析器組合對象( this.resolvers)列表如下所示：

為什么稱之為參數(shù)解析器組合對象？其實這里的this.resolvers并不是具體的參數(shù)解析器而是argumentResolvers、argumentResolverCache組合而成的HandlerMethodArgumentResolverComposite！

可以看到起還有argumentResolverCache屬性，其值列表如下：

默認(rèn)argumentResolverCache是一個容量為256的ConcurrentHashMap，是HandlerMethodArgumentResolverComposite的成員變量：

private final Map<MethodParameter, HandlerMethodArgumentResolver> argumentResolverCache =new ConcurrentHashMap<>(256);

這個argumentResolverCache是在動態(tài)改變，其在判斷是否支持paramter的方法中會改變，HandlerMethodArgumentResolverComposite.getArgumentResolver源碼如下：

private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {//如果緩存中有，則直接返回HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);//如果緩存中沒有就嘗試從解析器列表中獲取一個支持parameter的，并將解析器 parameter放入緩存if (result == null) {for (HandlerMethodArgumentResolver resolver : this.argumentResolvers) {if (resolver.supportsParameter(parameter)) {result = resolver;this.argumentResolverCache.put(parameter, result);break;}}}return result;}

為什么要有argumentResolverCache ？你可以沒有，但是你就需要每次從argumentResolvers遍歷尋找支持當(dāng)前MethodParameter的參數(shù)解析器！之所以保存一份鍵值對數(shù)據(jù)到argumentResolverCache ，就是為了下次不用尋找，就是為了更快！

ok ,引申多了。咱們繼續(xù)回去看如何解析參數(shù)獲取到參數(shù)值！

args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);

這里會調(diào)用HandlerMethodArgumentResolverComposite.resolveArgument方法：

public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {//這里獲取具體的、實際的參數(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.');}return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);}

獲取的實際的參數(shù)解析器如下所示(是RequestResponseBodyMethodProcessor)：

調(diào)用RequestResponseBodyMethodProcessor.resolveArgument解析參數(shù)：

public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {//這里獲取具體的、實際的參數(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.');}return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);}

獲取方法參數(shù)變量名稱String name = Conventions.getVariableNameForParameter(parameter);Conventions.getVariableNameForParameter方法源碼如下：

public static String getVariableNameForParameter(MethodParameter parameter) {Assert.notNull(parameter, 'MethodParameter must not be null');Class<?> valueClass;boolean pluralize = false;String reactiveSuffix = '';//判斷參數(shù)類型是不是數(shù)組if (parameter.getParameterType().isArray()) {valueClass = parameter.getParameterType().getComponentType();pluralize = true;}// 判斷是不是集合類型else if (Collection.class.isAssignableFrom(parameter.getParameterType())) {valueClass = ResolvableType.forMethodParameter(parameter).asCollection().resolveGeneric();if (valueClass == null) {throw new IllegalArgumentException('Cannot generate variable name for non-typed Collection parameter type');}pluralize = true;}else {//獲取參數(shù)類型，這里是com.alibaba.fastjson.JSONObjectvalueClass = parameter.getParameterType();ReactiveAdapter adapter = ReactiveAdapterRegistry.getSharedInstance().getAdapter(valueClass);if (adapter != null && !adapter.getDescriptor().isNoValue()) {reactiveSuffix = ClassUtils.getShortName(valueClass);valueClass = parameter.nested().getNestedParameterType();}}String name = ClassUtils.getShortNameAsProperty(valueClass);return (pluralize ? pluralize(name) : name + reactiveSuffix);}

拿到參數(shù)變量名與參數(shù)值后，就會進(jìn)行數(shù)據(jù)綁定過程。在這個過程中會使用binderFactory創(chuàng)建WebDataBinder對象，然后使用WebBindingInitializer對其進(jìn)行初始化。

if (binderFactory != null) {WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);if (arg != null) {validateIfApplicable(binder, parameter);if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());}}if (mavContainer != null) {mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());}}

首先我們看一下WebDataBinder實例對象創(chuàng)建過程。DefaultDataBinderFactory.createBinder方法源碼如下：

public final WebDataBinder createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName) throws Exception {//創(chuàng)建WebDataBinder 實例WebDataBinder dataBinder = createBinderInstance(target, objectName, webRequest);//如果初始化器不為null，進(jìn)行初始化if (this.initializer != null) {this.initializer.initBinder(dataBinder, webRequest);}//這是擴(kuò)展接口，可以用戶自定義以進(jìn)行更深入的初始化initBinder(dataBinder, webRequest);return dataBinder;}

繼續(xù)跟createBinderInstance(target, objectName, webRequest);，其會走到ServletRequestDataBinderFactory.createBinderInstance方法，如下所示：

可以發(fā)現(xiàn)器創(chuàng)建了一個ExtendedServletRequestDataBinder實例對象，其類繼承圖如下：

創(chuàng)建ExtendedServletRequestDataBinder實例對象時，一路調(diào)用父類的構(gòu)造方法，最終跟到DataBinder類中：

public DataBinder(@Nullable Object target, String objectName) { this.ignoreUnknownFields = true; this.ignoreInvalidFields = false; this.autoGrowNestedPaths = true; this.autoGrowCollectionLimit = 256; this.bindingErrorProcessor = new DefaultBindingErrorProcessor(); this.validators = new ArrayList(); this.target = ObjectUtils.unwrapOptional(target); this.objectName = objectName; }

創(chuàng)建完數(shù)據(jù)綁定器后，就使用初始化器對其進(jìn)行初始化，ConfigurableWebBindingInitializer.initBinder方法如下所示：

public void initBinder(WebDataBinder binder) {binder.setAutoGrowNestedPaths(this.autoGrowNestedPaths);if (this.directFieldAccess) {binder.initDirectFieldAccess();}if (this.messageCodesResolver != null) {binder.setMessageCodesResolver(this.messageCodesResolver);}if (this.bindingErrorProcessor != null) {binder.setBindingErrorProcessor(this.bindingErrorProcessor);}//如果target不為null且校驗器不為空，就綁定校驗器if (this.validator != null && binder.getTarget() != null &&this.validator.supports(binder.getTarget().getClass())) {binder.setValidator(this.validator);}//綁定類型轉(zhuǎn)換服務(wù)類if (this.conversionService != null) {binder.setConversionService(this.conversionService);}if (this.propertyEditorRegistrars != null) {for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {propertyEditorRegistrar.registerCustomEditors(binder);}}}

代碼如下所示，初始化完WebDataBinder后，就嘗試使用binder的校驗器對parameter進(jìn)行校驗(如果參數(shù)使用了@Valid注解或者以Valid開頭的注解)。校驗完后就會獲取org.springframework.validation.BeanPropertyBindingResult，如果BeanPropertyBindingResult有錯誤且你并沒有用一個Errors對象的參數(shù)接收異常，那么就會拋出MethodArgumentNotValidException異常！

public void initBinder(WebDataBinder binder) {binder.setAutoGrowNestedPaths(this.autoGrowNestedPaths);if (this.directFieldAccess) {binder.initDirectFieldAccess();}if (this.messageCodesResolver != null) {binder.setMessageCodesResolver(this.messageCodesResolver);}if (this.bindingErrorProcessor != null) {binder.setBindingErrorProcessor(this.bindingErrorProcessor);}//如果target不為null且校驗器不為空，就綁定校驗器if (this.validator != null && binder.getTarget() != null &&this.validator.supports(binder.getTarget().getClass())) {binder.setValidator(this.validator);}//綁定類型轉(zhuǎn)換服務(wù)類if (this.conversionService != null) {binder.setConversionService(this.conversionService);}if (this.propertyEditorRegistrars != null) {for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {propertyEditorRegistrar.registerCustomEditors(binder);}}}

數(shù)據(jù)綁定這一塊就是參數(shù)從形參變?yōu)閷崊⒌淖詈笠徊剑∪绾伟颜埱笾械膮?shù)值賦給方法的形參，就是通過WebDataBinder 這個對象實現(xiàn)的！可以看下此時binder對象：

有了綁定結(jié)果后的binder：

繼續(xù)往下走mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());把綁定結(jié)果放到model中：

OK！回到HandlerMethodArgumentResolverComposite.resolveArgument!

然后繼續(xù)回到InvocableHandlerMethod.getMethodArgumentValues中：

因為本次請求的目標(biāo)方法只有一個參數(shù)，則其會繼續(xù)返回到InvocableHandlerMethod.invokeForRequest，也就是說到此，① 已經(jīng)結(jié)束！

② 根據(jù)參數(shù)值反射調(diào)用目標(biāo)方法

InvocableHandlerMethod.doInvoke方法源碼如下：

protected Object doInvoke(Object... args) throws Exception {//獲取橋接方法并使方法可以調(diào)用ReflectionUtils.makeAccessible(getBridgedMethod());try {//獲取橋接方法以及對應(yīng)的bean 參數(shù)值，然后反射調(diào)用return getBridgedMethod().invoke(getBean(), args);}catch (IllegalArgumentException ex) {assertTargetBean(getBridgedMethod(), getBean(), args);String text = (ex.getMessage() != null ? ex.getMessage() : 'Illegal argument');throw new IllegalStateException(formatInvokeError(text, args), ex);}catch (InvocationTargetException ex) {// Unwrap for HandlerExceptionResolvers ...Throwable targetException = ex.getTargetException();if (targetException instanceof RuntimeException) {throw (RuntimeException) targetException;}else if (targetException instanceof Error) {throw (Error) targetException;}else if (targetException instanceof Exception) {throw (Exception) targetException;}else {throw new IllegalStateException(formatInvokeError('Invocation failure', args), targetException);}}}

這里就會反射調(diào)用目標(biāo)方法進(jìn)行處理！處理完后會再次返回，一直返回到ServletInvocableHandlerMethod.invokeAndHandle!

到此【3.1】結(jié)束！已經(jīng)調(diào)用了目標(biāo)方法并獲取到了目標(biāo)方法返回值！

【3.2】返回結(jié)果處理

ServletInvocableHandlerMethod.invokeAndHandle方法首先會反射調(diào)用目標(biāo)方法，然后拿到方法返回值。最后會根據(jù)returnValueHandlers對返回結(jié)果進(jìn)行處理！

this.returnValueHandlers.handleReturnValue(returnValue, getReturnValueType(returnValue), mavContainer, webRequest);

這里this.returnValueHandlers同樣是一個返回結(jié)果處理器組合對象，值列表如下：

① 獲取返回結(jié)果類型

HandlerMethod.getReturnValueType源碼如下：

public MethodParameter getReturnValueType(@Nullable Object returnValue) {return new ReturnValueMethodParameter(returnValue);}

ReturnValueMethodParameter是HandlerMethod的內(nèi)部類，并繼承自HandlerMethod.HandlerMethodParameter(沒錯，這貨也是HandlerMethod的內(nèi)部類)：

private class ReturnValueMethodParameter extends HandlerMethodParameter {@Nullableprivate final Object returnValue;public ReturnValueMethodParameter(@Nullable Object returnValue) {super(-1);this.returnValue = returnValue;}protected ReturnValueMethodParameter(ReturnValueMethodParameter original) {super(original);this.returnValue = original.returnValue;}@Overridepublic Class<?> getParameterType() {return (this.returnValue != null ? this.returnValue.getClass() : super.getParameterType());}@Overridepublic ReturnValueMethodParameter clone() {return new ReturnValueMethodParameter(this);}}

② 選擇HandlerMethodReturnValueHandler

HandlerMethodReturnValueHandlerComposite.handleReturnValue方法源碼如下：

private class ReturnValueMethodParameter extends HandlerMethodParameter {@Nullableprivate final Object returnValue;public ReturnValueMethodParameter(@Nullable Object returnValue) {super(-1);this.returnValue = returnValue;}protected ReturnValueMethodParameter(ReturnValueMethodParameter original) {super(original);this.returnValue = original.returnValue;}@Overridepublic Class<?> getParameterType() {return (this.returnValue != null ? this.returnValue.getClass() : super.getParameterType());}@Overridepublic ReturnValueMethodParameter clone() {return new ReturnValueMethodParameter(this);}}

這里returnType如下所示，其是HandlerMethod$ReturnValueMethodParameter對象：

這里尋找到的Handler是RequestResponseBodyMethodProcessor：

還記得上面解析參數(shù)時，咱們獲取到的實際參數(shù)解析器也是這個RequestResponseBodyMethodProcessor！

也就是說RequestResponseBodyMethodProcessor就是用來處理@RequestBody和@ResponseBody的！它可以使用HttpMessageConverter從請求中讀數(shù)據(jù)賦給參數(shù)，并可以把返回結(jié)果扔給響應(yīng)。HttpMessageConverter在這中間起到了什么作用呢？顧名思義，數(shù)據(jù)格式轉(zhuǎn)換！

其類結(jié)構(gòu)繼承圖如下：

③ 返回結(jié)果寫到outputMessage中

RequestResponseBodyMethodProcessor.handleReturnValue源碼如下：

@Overridepublic void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,ModelAndViewContainer mavContainer, NativeWebRequest webRequest)throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {//設(shè)置請求已經(jīng)被處理mavContainer.setRequestHandled(true);//獲取一個ServletServerHttpRequest實例-構(gòu)造函數(shù)參數(shù)為HttpServletRequestServletServerHttpRequest inputMessage = createInputMessage(webRequest);//獲取一個 實例ServletServerHttpResponse ，構(gòu)造函數(shù)參數(shù)為HttpServletResponseServletServerHttpResponse outputMessage = createOutputMessage(webRequest);// Try even with null return value. ResponseBodyAdvice could get involved.writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);}

記得在上面解析參數(shù)的時候調(diào)用過readWithMessageConverters方法，那時是從請求中獲取數(shù)據(jù)。這里返回響應(yīng)信息需要把返回結(jié)果寫到響應(yīng)體中。

AbstractMessageConverterMethodProcessor.writeWithMessageConverters源碼如下：

protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {Object body;Class<?> valueType;Type targetType;if (value instanceof CharSequence) {body = value.toString();valueType = String.class;targetType = String.class;}else {body = value;//值類型，這里是class com.baby.healthcare.common.ResponseBeanvalueType = getReturnValueType(body, returnType);targetType = GenericTypeResolver.resolveType(getGenericType(returnType), returnType.getContainingClass());}//判斷是否Resource 或InputStreamSourceif (isResourceType(value, returnType)) {outputMessage.getHeaders().set(HttpHeaders.ACCEPT_RANGES, 'bytes');if (value != null && inputMessage.getHeaders().getFirst(HttpHeaders.RANGE) != null &&outputMessage.getServletResponse().getStatus() == 200) {Resource resource = (Resource) value;try {List<HttpRange> httpRanges = inputMessage.getHeaders().getRange();outputMessage.getServletResponse().setStatus(HttpStatus.PARTIAL_CONTENT.value());body = HttpRange.toResourceRegions(httpRanges, resource);valueType = body.getClass();targetType = RESOURCE_REGION_LIST_TYPE;}catch (IllegalArgumentException ex) {outputMessage.getHeaders().set(HttpHeaders.CONTENT_RANGE, 'bytes */' + resource.contentLength());outputMessage.getServletResponse().setStatus(HttpStatus.REQUESTED_RANGE_NOT_SATISFIABLE.value());}}}MediaType selectedMediaType = null;//響應(yīng)內(nèi)容類型MediaType contentType = outputMessage.getHeaders().getContentType();boolean isContentTypePreset = contentType != null && contentType.isConcrete();if (isContentTypePreset) {if (logger.isDebugEnabled()) {logger.debug('Found ’Content-Type:' + contentType + '’ in response');}selectedMediaType = contentType;}else {HttpServletRequest request = inputMessage.getServletRequest();//獲取接收的MediaTypeList<MediaType> acceptableTypes = getAcceptableMediaTypes(request);//獲取返回結(jié)果的MediaTypeList<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);//如果body不為空，但是沒有合適的返回結(jié)果類型，則拋出異常if (body != null && producibleTypes.isEmpty()) {throw new HttpMessageNotWritableException('No converter found for return value of type: ' + valueType);}//循環(huán)比較，從acceptableTypes找到適配producibleTypes的List<MediaType> mediaTypesToUse = new ArrayList<>();for (MediaType requestedType : acceptableTypes) {for (MediaType producibleType : producibleTypes) {if (requestedType.isCompatibleWith(producibleType)) {mediaTypesToUse.add(getMostSpecificMediaType(requestedType, producibleType));}}}if (mediaTypesToUse.isEmpty()) {if (body != null) {throw new HttpMediaTypeNotAcceptableException(producibleTypes);}if (logger.isDebugEnabled()) {logger.debug('No match for ' + acceptableTypes + ', supported: ' + producibleTypes);}return;}//對MediaType進(jìn)行排序MediaType.sortBySpecificityAndQuality(mediaTypesToUse);for (MediaType mediaType : mediaTypesToUse) {if (mediaType.isConcrete()) {selectedMediaType = mediaType;break;}else if (mediaType.isPresentIn(ALL_APPLICATION_MEDIA_TYPES)) {selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;break;}}if (logger.isDebugEnabled()) {logger.debug('Using ’' + selectedMediaType + '’, given ' +acceptableTypes + ' and supported ' + producibleTypes);}}if (selectedMediaType != null) {selectedMediaType = selectedMediaType.removeQualityValue();for (HttpMessageConverter<?> converter : this.messageConverters) {GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?(GenericHttpMessageConverter<?>) converter : null);if (genericConverter != null ?((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :converter.canWrite(valueType, selectedMediaType)) {body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,(Class<? extends HttpMessageConverter<?>>) converter.getClass(),inputMessage, outputMessage);if (body != null) {Object theBody = body;LogFormatUtils.traceDebug(logger, traceOn ->'Writing [' + LogFormatUtils.formatValue(theBody, !traceOn) + ']');addContentDispositionHeader(inputMessage, outputMessage);if (genericConverter != null) {genericConverter.write(body, targetType, selectedMediaType, outputMessage);}else {((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);}}else {if (logger.isDebugEnabled()) {logger.debug('Nothing to write: null body');}}return;}}}if (body != null) {Set<MediaType> producibleMediaTypes =(Set<MediaType>) inputMessage.getServletRequest().getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);if (isContentTypePreset || !CollectionUtils.isEmpty(producibleMediaTypes)) {throw new HttpMessageNotWritableException('No converter for [' + valueType + '] with preset Content-Type ’' + contentType + '’');}throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes);}}

關(guān)于MediaType、MimeType與ContType對照表可以參考博文：ContentType與MIME對照表

循環(huán)比較，從acceptableTypes找到適配producibleTypes的：

//循環(huán)比較，從acceptableTypes找到適配producibleTypes的List<MediaType> mediaTypesToUse = new ArrayList<>();for (MediaType requestedType : acceptableTypes) {for (MediaType producibleType : producibleTypes) {if (requestedType.isCompatibleWith(producibleType)) {mediaTypesToUse.add(getMostSpecificMediaType(requestedType, producibleType));}}}

請求接收的內(nèi)容類型與返回響應(yīng)的內(nèi)容類型如下所示：

MediaType.sortBySpecificityAndQuality(mediaTypesToUse);對mediaTypesToUse進(jìn)行排序，排序后的效果如下所示：

尋找合適的轉(zhuǎn)換器把body寫到outputMessage中：

for (HttpMessageConverter<?> converter : this.messageConverters) {GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?(GenericHttpMessageConverter<?>) converter : null);if (genericConverter != null ?((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :converter.canWrite(valueType, selectedMediaType)) {body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,(Class<? extends HttpMessageConverter<?>>) converter.getClass(),inputMessage, outputMessage);if (body != null) {Object theBody = body;LogFormatUtils.traceDebug(logger, traceOn ->'Writing [' + LogFormatUtils.formatValue(theBody, !traceOn) + ']');addContentDispositionHeader(inputMessage, outputMessage);if (genericConverter != null) {genericConverter.write(body, targetType, selectedMediaType, outputMessage);}else {((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);}}else {if (logger.isDebugEnabled()) {logger.debug('Nothing to write: null body');}}return;}}

這里遍歷的messageConverters如下所示：

genericConverter.write(body, targetType, selectedMediaType, outputMessage);最后使用MappingJackson2HttpMessageConverter把body寫到outputMessage中。其類結(jié)構(gòu)繼承示意圖如下：

往響應(yīng)輸出流中寫完返回結(jié)果并flush后就會依次返回，此時【3.2】HandlerMethodReturnValueHandlerComposite.handleReturnValue返回結(jié)果處理執(zhí)行完畢！

然后返回到ServletInvocableHandlerMethod.invokeAndHandle,此時【3】執(zhí)行完畢！

【4】RequestMappingHandlerAdapter.getModelAndView嘗試獲取視圖對象

RequestMappingHandlerAdapter.getModelAndView方法源碼如下：

@Nullableprivate ModelAndView getModelAndView(ModelAndViewContainer mavContainer,ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {//更新modelmodelFactory.updateModel(webRequest, mavContainer);//如果請求已經(jīng)處理完，則直接返回，不會再嘗試創(chuàng)建mav if (mavContainer.isRequestHandled()) {return null;}ModelMap model = mavContainer.getModel();ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());if (!mavContainer.isViewReference()) {mav.setView((View) mavContainer.getView());}if (model instanceof RedirectAttributes) {Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);if (request != null) {RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);}}return mav;}

① modelFactory.updateModel(webRequest, mavContainer);更新model

② 如果請求處理完畢，則直接返回null

如下圖所示，在【3.2】-③中handleReturnValue首先將requestHandled設(shè)置為true。那么自然不會往下走去獲取視圖名并嘗試解析

【5】ServletWebRequest.requestCompleted

ServletWebRequest類繼承示意圖如下：

其會直接調(diào)用AbstractRequestAttributes.requestCompleted,方法源碼如下：

#標(biāo)記這個請求已經(jīng)被完成##調(diào)用所有的銷毀回調(diào)方法##更新請求過程中訪問到的會話屬性public void requestCompleted() {executeRequestDestructionCallbacks();updateAccessedSessionAttributes();this.requestActive = false;}

AbstractRequestAttributes.executeRequestDestructionCallbacks源碼如下，其會遍歷requestDestructionCallbacks并依次執(zhí)行每個Runnable。

private void executeRequestDestructionCallbacks() {//這里使用synchronized 保證每個runnable 只被調(diào)用一次synchronized (this.requestDestructionCallbacks) {for (Runnable runnable : this.requestDestructionCallbacks.values()) {runnable.run();}this.requestDestructionCallbacks.clear();}}

然后依次返回到RequestMappingHandlerAdapter.handleInternal也就是【1】-②:

如果響應(yīng)頭中不包含緩存控制Cache-Control,則嘗試對response進(jìn)行Cache-Control設(shè)置：

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

然后會返回到AbstractHandlerMethodAdapter.handle方法，然后回到DispatcherServlet.doDispatch,這是獲取到的MV為null。

【6】DispatcherServlet剩下的處理

① applyDefaultViewName(processedRequest, mv);嘗試獲取視圖名字

源碼如下所示，這里MV為null，自然不存在view name。

private void applyDefaultViewName(HttpServletRequest request, @Nullable ModelAndView mv) throws Exception {if (mv != null && !mv.hasView()) {String defaultViewName = getDefaultViewName(request);if (defaultViewName != null) {mv.setViewName(defaultViewName);}}}

② mappedHandler.applyPostHandle(processedRequest, response, mv);方法后置處理

其實就是執(zhí)行攔截器的后置方法postHandle，HandlerExecutionChain.applyPostHandle源碼如下：

void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)throws Exception {HandlerInterceptor[] interceptors = getInterceptors();if (!ObjectUtils.isEmpty(interceptors)) {for (int i = interceptors.length - 1; i >= 0; i--) {HandlerInterceptor interceptor = interceptors[i];interceptor.postHandle(request, response, this.handler, mv);}}}

③ processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

如果存在異常，則MV為 ((ModelAndViewDefiningException) exception).getModelAndView();然后進(jìn)行render(mv, request, response);;

如果不存在異常，且MV不為null，則進(jìn)行render(mv, request, response);;

如果MV不存在，則不會進(jìn)行render(mv, request, response);;，其會直接調(diào)用mappedHandler.triggerAfterCompletion(request, response, null);。

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

攔截器的完成方法afterCompletion調(diào)用，HandlerExecutionChain.triggerAfterCompletion方法源碼如下：

void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex)throws Exception {HandlerInterceptor[] interceptors = getInterceptors();if (!ObjectUtils.isEmpty(interceptors)) {for (int i = this.interceptorIndex; i >= 0; i--) {HandlerInterceptor interceptor = interceptors[i];try {interceptor.afterCompletion(request, response, this.handler, ex);}catch (Throwable ex2) {logger.error('HandlerInterceptor.afterCompletion threw exception', ex2);}}}}

最后執(zhí)行finally 里面的邏輯：

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);}}

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