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 {
// 檢查多部件請求
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
// 標記1：根據給定的request獲取當前請求的handler
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
// 標記2： 確定適配器
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
// 獲取請求方法
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
// 攔截器前置處理
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
// 標記3： 執行目標方法
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
// 申請默認視圖名
applyDefaultViewName(processedRequest, mv);
// 攔截器的後置處理方法
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);
}
// 標記4：結果處理
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);
}
}
}
}// 標記1：根據給定的request獲取當前請求的handler
mappedHandler = getHandler(processedRequest); /**
* Return the HandlerExecutionChain for this request. // 返回當前請求的執行鏈
* <p>Tries all handler mappings in order. // 按序循環查找所有的handler mappings
* @param request current HTTP request
* @return the HandlerExecutionChain, or {@code null} if no handler could be found
*/
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// for循環遍歷所有的handlerMapping
// 注1：這裏的handlerMapping是在初始化策略中加載的springMVC的默認的handler， 初始化策略在dispatcher的intiStrategies()方法中
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
// 根據handlerMapping獲取handler執行鏈，包含攔截器interceptor和處理器handler
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}AbstractHandlerMapping的getHandler(request)方法：
/**
* Look up a handler for the given request, falling back to the default
* handler if no specific one is found.
* @param request current HTTP request
* @return the corresponding handler instance, or the default handler
* @see #getHandlerInternal
*/
@Override
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// 獲取handler
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 = getApplicationContext().getBean(handlerName);
}
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}AbstractUrlHandlerMappinggetHandlerInternal(HttpServletRequest request) AbstractHandlerMethodMapping的getHandlerInternal()方法：
/**
* Look up a handler method for the given request.
*/
@Override
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
if (logger.isDebugEnabled()) {
logger.debug("Looking up handler method for path " + lookupPath);
}
this.mappingRegistry.acquireReadLock();
try {
// 查找handlerMethod處理器方法
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
if (logger.isDebugEnabled()) {
if (handlerMethod != null) {
logger.debug("Returning handler method [" + handlerMethod + "]");
}
else {
logger.debug("Did not find handler method for [" + lookupPath + "]");
}
}
return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
}
finally {
this.mappingRegistry.releaseReadLock();
}
} /**
* Return the HandlerAdapter for this handler object. 找到handler的適配器，遍歷初始化策略加載的所有適配器
* @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 {
for (HandlerAdapter ha : this.handlerAdapters) {
if (logger.isTraceEnabled()) {
logger.trace("Testing handler adapter [" + ha + "]");
}
if (ha.supports(handler)) {
return ha;
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
} /**
* Apply preHandle methods of registered interceptors. 攔截器前置處理
* @return {@code true} if the execution chain should proceed with the
* next interceptor or the handler itself. Else, DispatcherServlet assumes
* that this interceptor has already dealt with the response itself.
*/
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
// 遍歷所有的攔截器進行前置處理
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
// 執行目標方法
@Override
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler);
} protected ModelAndView handleInternal(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
this.checkRequest(request);
ModelAndView mav;
// 是否需要在同步塊中執行目標方法
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized(mutex) {
mav = this.invokeHandlerMethod(request, response, handlerMethod);
}
} else {
mav = this.invokeHandlerMethod(request, response, handlerMethod);
}
} else {
// 執行處理器方法
mav = this.invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader("Cache-Control")) {
if (this.getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
this.applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
} else {
this.prepareResponse(response);
}
}
return mav;
}
/**
* Invoke the {@link RequestMapping} handler method preparing a {@link ModelAndView}
* if view resolution is required.
* @since 4.2
* @see #createInvocableHandlerMethod(HandlerMethod)
*/
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);
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
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();
if (logger.isDebugEnabled()) {
logger.debug("Found concurrent result value [" + result + "]");
}
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
HandlerMapping初始化：
/**
* Initialize the strategy objects that this servlet uses. 初始化該servlet用到的策略組件
* <p>May be overridden in subclasses in order to initialize further strategy objects.
*/
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}