SpringMVC處理流程非常詳細(xì)的講解

作者：Springboot實(shí)戰(zhàn)案例錦集 2023-03-17 08:11:25

通過(guò)HandlerMapping找到了相應(yīng)的HandlerMethod對(duì)象，最后封裝到了HandlerExecutionChain中，接下來(lái)就是根據(jù)HandlerMethod查找合適的HandlerAdapter處理程序。

1 請(qǐng)求入口

public class DispatcherServlet extends FrameworkServlet {
   protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
     HandlerExecutionChain mappedHandler = null;
     try {
       ModelAndView mv = null;
       Exception dispatchException = null;
       try {
         // 2.1.通過(guò)HandlerMapping獲取請(qǐng)求處理鏈，該對(duì)象由處理程序（Controller，一般HandlerMethod對(duì)象）及攔截器（Interceptor）組成
         mappedHandler = getHandler(processedRequest);
         if (mappedHandler == null) {
           noHandlerFound(processedRequest, response);
           return;
         }
         // 2.2.根據(jù)2.1獲取的處理程序（HandlerMethod）對(duì)象確定能夠處理該處理程序的HandlerAdapter對(duì)象
         HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
         // ...
         // 2.3.執(zhí)行處理程序之前，執(zhí)行攔截器preHandle方法，如果返回了false，本次請(qǐng)求將被終止
         if (!mappedHandler.applyPreHandle(processedRequest, response)) {
           return;
         }
 
         // 2.4.真正的執(zhí)行處理程序
         mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
         // ...
         // 2.5.執(zhí)行處理程序之后，執(zhí)行攔截器postHandle方法
         mappedHandler.applyPostHandle(processedRequest, response, mv);
       } catch (Exception ex) {
         dispatchException = ex;
       } catch (Throwable err) {
         dispatchException = new NestedServletException("Handler dispatch failed", err);
       }
       // 2.6.處理結(jié)果，根據(jù)處理程序是否發(fā)生異常，是否返回有ModelAndView對(duì)象進(jìn)行結(jié)果的處理
       processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
     }
     // ...
   }
 }

2 處理請(qǐng)求

2.1 獲取請(qǐng)求處理鏈

該步驟通過(guò)HandlerMapping獲取HandlerExecutionChain處理器執(zhí)行鏈。

public class DispatcherServlet {
   protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
     if (this.handlerMappings != null) {
       // 遍歷當(dāng)前容器中注冊(cè)的所有HandlerMapping對(duì)象
       for (HandlerMapping mapping : this.handlerMappings) {
         // 針對(duì)Controller接口，使用的是RequestMappingHandlerMapping對(duì)象
         HandlerExecutionChain handler = mapping.getHandler(request);
         if (handler != null) {
           return handler;
         }
       }
     }
     return null;
   }
 }

這里以RequestMappingHandlerMapping為例

mapping.getHandler(request)方法調(diào)用流程如下：

public abstract class AbstractHandlerMapping {
   public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
     // 調(diào)用子類實(shí)現(xiàn)的getHandlerInternal方法
     Object handler = getHandlerInternal(request);
     // ...
     // 根據(jù)查找到的處理程序封裝到處理程序執(zhí)行鏈
     // 這里會(huì)將攔截器也添加其中
     HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
     // ...這里是跨域相關(guān)的配置
     return executionChain;
   }
   protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
     HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
         (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
     for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
       if (interceptor instanceof MappedInterceptor) {
         MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
         if (mappedInterceptor.matches(request)) {
           chain.addInterceptor(mappedInterceptor.getInterceptor());
         }
       } else {
         chain.addInterceptor(interceptor);
       }
     }
     return chain;
   }
 }

調(diào)用子類RequestMappingInfoHandlerMapping#getHandlerInternal實(shí)現(xiàn)。

public abstract class RequestMappingInfoHandlerMapping extends AbstractHandlerMethodMapping<RequestMappingInfo> {
   protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
     request.removeAttribute(PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
     try {
       // 又調(diào)父類的實(shí)現(xiàn) (⊙o⊙)…
       return super.getHandlerInternal(request);
     }
   }
}

調(diào)用父類AbstractHandlerMethodMapping#getHandlerInternal方法

public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMapping implements InitializingBean {
   private final MappingRegistry mappingRegistry = new MappingRegistry();
   protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
     // 根據(jù)當(dāng)前的請(qǐng)求獲取請(qǐng)求的uri
     String lookupPath = initLookupPath(request);
     this.mappingRegistry.acquireReadLock();
     try {
       HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
       return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
     }
   }
   protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
     List<Match> matches = new ArrayList<>();
     // 系統(tǒng)啟動(dòng)時(shí)初始化RequestMappingHandlerMapping解析了整個(gè)系統(tǒng)中所有的Controller然后注冊(cè)到MappingRegistry中
     // 根據(jù)當(dāng)前的請(qǐng)求uri，對(duì)應(yīng)List<RequestMappingInfo>對(duì)象,相同的uri可能對(duì)應(yīng)不同的request method，所以這里返回的是List集合
     List<T> directPathMatches = this.mappingRegistry.getMappingsByDirectPath(lookupPath);
     if (directPathMatches != null) {
       // 該方法內(nèi)部會(huì)根據(jù)找到的RequestMappingInfo進(jìn)行遍歷，根據(jù)請(qǐng)求信息逐個(gè)的判斷對(duì)應(yīng)@RequestMapping配置的屬性是否匹配
       addMatchingMappings(directPathMatches, matches, request);
     }
     if (matches.isEmpty()) {
       addMatchingMappings(this.mappingRegistry.getRegistrations().keySet(), matches, request);
     }
     // 下面if的邏輯就是判斷如果找到了匹配并且存在多個(gè)會(huì)找出最合適的
     if (!matches.isEmpty()) {
       Match bestMatch = matches.get(0);
       if (matches.size() > 1) {
         Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
         matches.sort(comparator);
         bestMatch = matches.get(0);
         if (CorsUtils.isPreFlightRequest(request)) {
           for (Match match : matches) {
             if (match.hasCorsConfig()) {
               return PREFLIGHT_AMBIGUOUS_MATCH;
             }
           }
         } else {
           Match secondBestMatch = matches.get(1);
           if (comparator.compare(bestMatch, secondBestMatch) == 0) {
             Method m1 = bestMatch.getHandlerMethod().getMethod();
             Method m2 = secondBestMatch.getHandlerMethod().getMethod();
             String uri = request.getRequestURI();
             throw new IllegalStateException(
                 "Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
           }
         }
       }
       request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.getHandlerMethod());
       // 將當(dāng)前請(qǐng)求uri保存到request對(duì)象中setAttribute
       handleMatch(bestMatch.mapping, lookupPath, request);
       // 返回當(dāng)前uri對(duì)應(yīng)的HandlerMethod對(duì)象
       return bestMatch.getHandlerMethod();
     }
   }
   protected void handleMatch(T mapping, String lookupPath, HttpServletRequest request) {
     request.setAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE, lookupPath);
   }
 }

2.2 獲取HandlerAdapter

在上一步中通過(guò)HandlerMapping找到了相應(yīng)的HandlerMethod對(duì)象，最后封裝到了HandlerExecutionChain中，接下來(lái)就是根據(jù)HandlerMethod查找合適的HandlerAdapter處理程序。

public class DispatcherServlet {
   protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
     if (this.handlerAdapters != null) {
       // 這里的參數(shù)handler一般都是HandlerMethod對(duì)象
       for (HandlerAdapter adapter : this.handlerAdapters) {
         // 這個(gè)根據(jù)handler判斷哪個(gè)HandlerAdapter支持，一般都是RequestMappingHandlerAdapter
         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");
   }
 }

RequestMappingHandlerAdapter 這調(diào)用的是父類方法

public abstract class AbstractHandlerMethodAdapter {
  public final boolean supports(Object handler) {
    return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
  }
}
public class RequestMappingHandlerAdapter {
  protected boolean supportsInternal(HandlerMethod handlerMethod) {
    return true;
  }
}

2.3 執(zhí)行攔截器preHandle方法

在真正調(diào)用處理程序前，執(zhí)行攔截器preHandle方法

public class HandlerExecutionChain {
   boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
     for (int i = 0; i < this.interceptorList.size(); i++) {
       HandlerInterceptor interceptor = this.interceptorList.get(i);
       // 如果任何一個(gè)攔截器返回了false，本次請(qǐng)求都會(huì)被終止
       if (!interceptor.preHandle(request, response, this.handler)) {
         // 該攔截器的完成回調(diào)會(huì)被執(zhí)行
         triggerAfterCompletion(request, response, null);
         return false;
       }
       this.interceptorIndex = i;
     }
     return true;
   }
 }

2.4 實(shí)際請(qǐng)求處理

public class DispatcherServlet {
   protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
     mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
   }
 }

AbstractHandlerMethodAdapter

public abstract class AbstractHandlerMethodAdapter {
   public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
       throws Exception {
     // 子類重寫(xiě)了該方法
     return handleInternal(request, response, (HandlerMethod) handler);
   }
 }

RequestMappingHandlerAdapter

public class RequestMappingHandlerAdapter {
   protected ModelAndView handleInternal(HttpServletRequest request, 
       HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
     ModelAndView mav;
     if (this.synchronizeOnSession) {
       // ...
     } else {
       // No synchronization on session demanded at all...
       // 執(zhí)行HandlerMethod調(diào)用
       mav = invokeHandlerMethod(request, response, handlerMethod);
     }
     // ...
     return mav;
   }
   protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
       HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
 
     ServletWebRequest webRequest = new ServletWebRequest(request, response);
     try {
       // 創(chuàng)建數(shù)據(jù)綁定工廠，主要作用就是將請(qǐng)求的參數(shù)信息與Controller方法的參數(shù)進(jìn)行綁定（數(shù)據(jù)類型的轉(zhuǎn)換）及參數(shù)校驗(yàn)
       WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
       // 處理@ModelAttribute和@SessionAttribute注解，它將做兩件事：
       // 1.將@SessionAttribute注解的方法的相關(guān)數(shù)據(jù)合并到下面的ModelAndViewContainer中
       // 2.將@ModelAttribute注解的方法返回值添加到ModelAndViewContainer中
       ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
       // 實(shí)際HandlerMethod調(diào)用對(duì)象
       ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
       if (this.argumentResolvers != null) {
         // 設(shè)置參數(shù)解析器
         invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
       }
       if (this.returnValueHandlers != null) {
         // 設(shè)置Controller方法返回值的處理器
         invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
       }
       invocableMethod.setDataBinderFactory(binderFactory);
       invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
 
       ModelAndViewContainer mavContainer = new ModelAndViewContainer();
       mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
       // 執(zhí)行上面說(shuō)的兩個(gè)步驟
       modelFactory.initModel(webRequest, mavContainer, invocableMethod);
       mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
       // ...
       // 執(zhí)行調(diào)用HandlerMethod
       // 在這個(gè)過(guò)程中會(huì)應(yīng)用到參數(shù)解析器和返回值處理器，這里就不展開(kāi)說(shuō)了
       invocableMethod.invokeAndHandle(webRequest, mavContainer);
       if (asyncManager.isConcurrentHandlingStarted()) {
         return null;
       }
       // 這里會(huì)返回ModelAndView對(duì)象，這個(gè)根據(jù)情況，如果你是RestController，那么在通過(guò)返回值處理器就已經(jīng)將結(jié)果進(jìn)行了輸出如使用@ResponseBody注解的方法
       // 如果是RestController，請(qǐng)求結(jié)果就提前輸出了，同時(shí)會(huì)將ModelAndViewContainer的requestHandled屬性設(shè)置為true。
       return getModelAndView(mavContainer, modelFactory, webRequest);
     } finally {
       webRequest.requestCompleted();
     }
   }
   private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
       ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
 
     modelFactory.updateModel(webRequest, mavContainer);
     // 如果是@ResponseBody注解的方法，那么直接返回null
     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());
     }
     // ...
     return mav;
   }
 }

2.5 執(zhí)行攔截器postHandle方法

public class HandlerExecutionChain {
   void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
       throws Exception {
     for (int i = this.interceptorList.size() - 1; i >= 0; i--) {
       HandlerInterceptor interceptor = this.interceptorList.get(i);
       interceptor.postHandle(request, response, this.handler, mv);
     }
   }
}

2.6 處理結(jié)果

public class DispatcherServlet {
   protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
     processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
   }
   private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
       @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
       @Nullable Exception exception) throws Exception {
 
     boolean errorView = false;
 
     // 在處理過(guò)程中如果出現(xiàn)了異常會(huì)進(jìn)入這里進(jìn)行異常處理
     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);
       }
     }
 
     // 如果Controller方法返回有ModelAndView
     if (mv != null && !mv.wasCleared()) {
       // 進(jìn)行視圖的渲染輸出到客戶端
       render(mv, request, response);
       if (errorView) {
         WebUtils.clearErrorRequestAttributes(request);
       }
     }
 
     if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
       // Concurrent handling started during a forward
       return;
     }
 
     // 如果是RestController接口，那么上面的代碼都不會(huì)執(zhí)行
     if (mappedHandler != null) {
       // 執(zhí)行攔截器的afterCompletion回調(diào)方法
       mappedHandler.triggerAfterCompletion(request, response, null);
     }
   }
 }