写出一个你自己的MVC框架-基于对springMVC源码实现和理解（6）：执行，调度和渲染（一）

数据初始化结束后，我们需要考虑对请求如何处理。回到springMVC源代码中，找到方法doService(),七七八八的一大片，想来想去核心的可能只有这句了：

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1. try {  
2.             doDispatch(request, response);  
3.         }  

我们再来看看doDispatch(),又是一大片:

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1. protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {  
2.         HttpServletRequest processedRequest = request;  
3.         HandlerExecutionChain mappedHandler = null;  
4.         boolean multipartRequestParsed = false;  
5.   
6.         WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);  
7.   
8.         try {  
9.             ModelAndView mv = null;  
10.             Exception dispatchException = null;  
11.   
12.             try {  
13.                 processedRequest = checkMultipart(request);  
14.                 multipartRequestParsed = (processedRequest != request);  
15.   
16.                 // Determine handler for the current request.  
17.                 mappedHandler = getHandler(processedRequest);  
18.                 if (mappedHandler == null || mappedHandler.getHandler() == null) {  
19.                     noHandlerFound(processedRequest, response);  
20.                     return;  
21.                 }  
22.   
23.                 // Determine handler adapter for the current request.  
24.                 HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());  
25.   
26.                 // Process last-modified header, if supported by the handler.  
27.                 String method = request.getMethod();  
28.                 boolean isGet = "GET".equals(method);  
29.                 if (isGet || "HEAD".equals(method)) {  
30.                     long lastModified = ha.getLastModified(request, mappedHandler.getHandler());  
31.                     if (logger.isDebugEnabled()) {  
32.                         logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);  
33.                     }  
34.                     if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {  
35.                         return;  
36.                     }  
37.                 }  
38.   
39.                 if (!mappedHandler.applyPreHandle(processedRequest, response)) {  
40.                     return;  
41.                 }  
42.   
43.                 try {  
44.                     // Actually invoke the handler.  
45.                     mv = ha.handle(processedRequest, response, mappedHandler.getHandler());  
46.                 }  
47.                 finally {  
48.                     if (asyncManager.isConcurrentHandlingStarted()) {  
49.                         return;  
50.                     }  
51.                 }  
52.   
53.                 applyDefaultViewName(request, mv);  
54.                 mappedHandler.applyPostHandle(processedRequest, response, mv);  
55.             }  
56.             catch (Exception ex) {  
57.                 dispatchException = ex;  
58.             }  
59.             processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);  
60.         }  
61.         catch (Exception ex) {  
62.             triggerAfterCompletion(processedRequest, response, mappedHandler, ex);  
63.         }  
64.         catch (Error err) {  
65.             triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);  
66.         }  
67.         finally {  
68.             if (asyncManager.isConcurrentHandlingStarted()) {  
69.                 // Instead of postHandle and afterCompletion  
70.                 mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);  
71.                 return;  
72.             }  
73.             // Clean up any resources used by a multipart request.  
74.             if (multipartRequestParsed) {  
75.                 cleanupMultipart(processedRequest);  
76.             }  
77.         }  
78.     }  

其实核心就是那么几个过程：

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1. mappedHandler = getHandler(processedRequest);  

获得了HandlerExecutionChain执行模块链。

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1. // Determine handler adapter for the current request.  
2.                 HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());  

获得request匹配的handlerAdapter

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1. if (!mappedHandler.applyPreHandle(processedRequest, response)) {  
2.                     return;  
3.                 }  

调用HandlerExecutionChain中所有拦截器的preHandler方法，根据返回值判断是否继续。

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1. try {  
2.                     // Actually invoke the handler.  
3.                     mv = ha.handle(processedRequest, response, mappedHandler.getHandler());  
4.                 }  

如果preHander都返回true则执行handler

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1. mappedHandler.applyPostHandle(processedRequest, response, mv);  

结束后执行postHande方法

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1. processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);  

完成页面渲染

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1. triggerAfterCompletion(processedRequest, response, mappedHandler, ex);  

最后根据判断结果执行各种afterCompletion