寫過(guò)java后端的好像沒有不會(huì)spring mvc的漆际，至于spring mvc的介紹優(yōu)點(diǎn)河泳，自行g(shù)oogle腾誉，在這里就不balabala的介紹了。

在分析spring mvc源碼之前呵俏，先看一張圖：

spring mvc.png

請(qǐng)求處理的過(guò)程：
1.DispatcherServelt作為前端控制器，攔截request對(duì)象春瞬。
2.DispatcherServlet接收到request對(duì)象之后柴信，查詢HandlerMapping,得到一個(gè)HandlerExecutionChain對(duì)象。
3.DispatcherServlet將Handler對(duì)象交由HandlerAdapter(適配器模式的典型應(yīng)用)宽气，調(diào)用相應(yīng)的controller方法随常。
4.Controller方法返回ModelAndView對(duì)象，DispatcherServlet將view交由ViewResolver進(jìn)行解析萄涯，得到相應(yīng)的視圖绪氛。用model渲染視圖。
5.返回響應(yīng)結(jié)果涝影。

整個(gè)過(guò)程的流程其實(shí)就是DispatcherServelt中doDispatch()方法的調(diào)用過(guò)程枣察。

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        //第一步攔截request對(duì)象，doDispatch()方法在doService()方法中被調(diào)用燃逻，request對(duì)象是經(jīng)過(guò)處理的序目。
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            ModelAndView mv = null;
            Exception dispatchException = null;

            try {
                //和文件的上傳和下載有關(guān)系，判斷請(qǐng)求的類型是否是multipart類型
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // Determine handler for the current request.
                //主要看這里伯襟，這里是得到HandlerExecutionChain的方法猿涨。關(guān)于Handler()方法向下看
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
                //這里已經(jīng)獲取到HandlerExecutionChain對(duì)象，接下來(lái)就要獲取HandlerAdapter對(duì)象姆怪，調(diào)用Handler對(duì)象的方法叛赚。
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // Process last-modified header, if supported by the handler
                //有關(guān)瀏覽器緩存的設(shè)定（304）
                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;
                    }
                }
                //pan'du
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

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

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }
                //解析視圖，數(shù)據(jù)渲染
                applyDefaultViewName(request, mv);
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                dispatchException = ex;
            }
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Error err) {
            triggerAfterCompletionWithError(processedRequest, response, mappedHandler, 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);
                }
            }
        }
    }

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        //遍歷HandlerMappingList對(duì)象（存儲(chǔ)若干個(gè)HandlerMapping對(duì)象）稽揭，不斷調(diào)用俺附，直到不為空為止，否則返回null
        for (HandlerMapping hm : this.handlerMappings) {
            if (logger.isTraceEnabled()) {
                logger.trace(
                        "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
            }
            HandlerExecutionChain handler = hm.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
        return null;
    }