spring mvc 請求處理流程

SpringMVC核心處理流程：

1川无、DispatcherServlet前端控制器接收發(fā)過來的請求，交給HandlerMapping處理器映射器

2枕稀、HandlerMapping處理器映射器，根據(jù)請求路徑找到相應(yīng)的HandlerAdapter處理器適配器（處理器適配器就是那些攔截器或Controller）

3、HandlerAdapter處理器適配器荞估，請求數(shù)據(jù)綁定和轉(zhuǎn)換貌笨，處理一些功能請求弱判，返回一個ModelAndView對象（包括模型數(shù)據(jù)、邏輯視圖名）

4锥惋、ViewResolver視圖解析器昌腰，先根據(jù)ModelAndView中設(shè)置的View解析具體視圖

5、然后再將Model模型中的數(shù)據(jù)渲染到View上

這些過程都是以DispatcherServlet為中軸線進(jìn)行的膀跌。

1.入口源碼

springMVC的請求會交由dispatcherServlet處理遭商，其本質(zhì)上是一個多線程的請求處理機(jī)制；核心業(yè)務(wù)邏輯被設(shè)計(jì)在doDispatcher(..)方法中捅伤；

/**
 * Process the actual dispatching to the handler.
 * <p>The handler will be obtained by applying the servlet's HandlerMappings in order.
 * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
 * to find the first that supports the handler class.
 * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
 * themselves to decide which methods are acceptable.
 * @param request current HTTP request
 * @param response current HTTP response
 * @throws Exception in case of any kind of processing failure
 */
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 {
         processedRequest = checkMultipart(request);
         multipartRequestParsed = (processedRequest != request);
 
          // 綁定url -> 具體的handler/Controller.method(..)
         // Determine handler for the current request.
         mappedHandler = getHandler(processedRequest);
         if (mappedHandler == null || mappedHandler.getHandler() == null) {
            noHandlerFound(processedRequest, response);
            return;
         }
 
         // 根據(jù)handler綁定具體的adapter
         // Determine handler adapter for the current request.
         HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
 
 
         // Process last-modified header, if supported by the handler.
         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;
            }
         }
 
         // interceptor 攔截器進(jìn)行前置預(yù)處理
         if (!mappedHandler.applyPreHandle(processedRequest, response)) {
            return;
         }
 
         // 在handle方法中進(jìn)行了請求數(shù)據(jù)的綁定劫流，方法invoke，返回model的處理和封裝等
         // Actually invoke the handler.
         mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
 
         if (asyncManager.isConcurrentHandlingStarted()) {
            return;
         }
 
         applyDefaultViewName(processedRequest, mv);
         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);
      }
      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);
         }
      }
   }
}

2.核心關(guān)注的幾個問題

2.1 請求如何路由到具體的Controller上的方法進(jìn)行處理?

根據(jù)請求路徑丛忆，與已知的handlerMapping進(jìn)行匹配祠汇，并加入interceptors:

dispatcherServlet.getHandler()最終調(diào)用AbstracteHandlerMapping.getHandlerExecutionChain(..)中
進(jìn)行url與handlerMapping進(jìn)行匹配，并加入interceptors;

2.2 扁平化的前端請求數(shù)據(jù)如何進(jìn)行數(shù)據(jù)綁定熄诡？

我們知道可很，前端的get/post等請求，會被requestServlet接受凰浮，并封裝成HttpServletRequest的parameterMap中我抠，每一項(xiàng)請求的數(shù)據(jù)結(jié)構(gòu)都是 K-V 形的姜骡。

image.png

那么在這個中間數(shù)據(jù)如何實(shí)現(xiàn)數(shù)據(jù)綁定到Bean圈澈，String格式的Value 轉(zhuǎn)換成各種目標(biāo)格式。

事實(shí)上尘惧，spring MVC將整個網(wǎng)絡(luò)請求的處理流程進(jìn)行了合理的切分,其大致的處理流程如下：

1.調(diào)用匹配到的adapter.handle(..)

2.然后調(diào)用invokeAndHandle(..)

3.調(diào)用invokeForRequest(..)獲取getMethodArgumentValues(..)獲取和綁定入?yún)?

4.在具體的方法中康栈，獲取支持處理的argumentResolvers,然后調(diào)用resolveArgument(..)方法;

5.在ModelAttributeMethodProcessor中調(diào)用bindRequestParameters(binder, webRequest),方法，然后再調(diào)用bind()進(jìn)行bean參數(shù)的綁定喷橙；

6.調(diào)用binder.convertIfNecessary(arg, parameter.getParameterType(), parameter)方法進(jìn)行參數(shù)的轉(zhuǎn)換啥么；

數(shù)據(jù)綁定調(diào)用堆棧

請求參數(shù)最初都是扁平化的