在面试的时候，面试官经常会问你对SpringMVC了解吗？大多数面试者多会说出SpringMVC的执行流程图，其实我觉得这也没有错，毕竟SpringMVC就是按照这一套流程执行的，下面就是该执行流程图：
今天我们就从源码的角度来看它到底是怎么执行的？下面这段代码它是DispatchServlet类中的doDispatch()方法，也就是我们上图的前端控制器
1 protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
2 HttpServletRequest processedRequest = request;
3 HandlerExecutionChain mappedHandler = null;
4 boolean multipartRequestParsed = false;
5 WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
6
7 try {
8 try {
9 ModelAndView mv = null;
10 Object dispatchException = null;
11
12 try {
13 processedRequest = this.checkMultipart(request);
14 multipartRequestParsed = processedRequest != request;
15 mappedHandler = this.getHandler(processedRequest);
16 if (mappedHandler == null) {
17 this.noHandlerFound(processedRequest, response);
18 return;
19 }
20
21 HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());
22 String method = request.getMethod();
23 boolean isGet = "GET".equals(method);
24 if (isGet || "HEAD".equals(method)) {
25 long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
26 if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
27 return;
28 }
29 }
30
31 if (!mappedHandler.applyPreHandle(processedRequest, response)) {
32 return;
33 }
34
35 mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
36 if (asyncManager.isConcurrentHandlingStarted()) {
37 return;
38 }
39
40 this.applyDefaultViewName(processedRequest, mv);
41 mappedHandler.applyPostHandle(processedRequest, response, mv);
42 } catch (Exception var20) {
43 dispatchException = var20;
44 } catch (Throwable var21) {
45 dispatchException = new NestedServletException("Handler dispatch failed", var21);
46 }
47
48 this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
49 } catch (Exception var22) {
50 this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22);
51 } catch (Throwable var23) {
52 this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23));
53 }
54
55 } finally {
56 if (asyncManager.isConcurrentHandlingStarted()) {
57 if (mappedHandler != null) {
58 mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
59 }
60 } else if (multipartRequestParsed) {
61 this.cleanupMultipart(processedRequest);
62 }
63
64 }
65 }
下图就是该方法重要的第一步，获取执行链
执行链中包含两个重要的属性，一个是handler(上图所说的handler)，另一个是HandlerInterceptor(处理器拦截器的集合)，下面再说这两个属性的作用
进入getHandler(...)方法
进入getHandler(...)这个方法
未完。。。。。。