释放双眼，带上耳机，听听看~！
————吾亦无他,唯手熟尔，谦卑若愚，好学若饥————-
先从概念理解，从中央调度器，携带参数request，调度到HandleMapping处理器映射器，处理器映射器返回处理器执行链给中央调度器
我从底层走一遍，印证这个概念：
1.都说是中央调度器的，所以先找到中央调度器DispatcherServlet
2.从他里面找到一个方法 ctrl+f 找（doDistch）
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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 err = null;
10 Exception dispatchException = null;
11
12 try {
13 processedRequest = this.checkMultipart(request);
14 multipartRequestParsed = processedRequest != request;
15 mappedHandler = this.getHandler(processedRequest);
16 if(mappedHandler == null || mappedHandler.getHandler() == null) {
17 this.noHandlerFound(processedRequest, response);
18 return;
19 }
20
21 HandlerAdapter ex = this.getHandlerAdapter(mappedHandler.getHandler());
22 String method = request.getMethod();
23 boolean isGet = "GET".equals(method);
24 if(isGet || "HEAD".equals(method)) {
25 long lastModified = ex.getLastModified(request, mappedHandler.getHandler());
26 if(this.logger.isDebugEnabled()) {
27 this.logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
28 }
29
30 if((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
31 return;
32 }
33 }
34
35 if(!mappedHandler.applyPreHandle(processedRequest, response)) {
36 return;
37 }
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39 err = ex.handle(processedRequest, response, mappedHandler.getHandler());
40 if(asyncManager.isConcurrentHandlingStarted()) {
41 return;
42 }
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44 this.applyDefaultViewName(processedRequest, err);
45 mappedHandler.applyPostHandle(processedRequest, response, err);
46 } catch (Exception var19) {
47 dispatchException = var19;
48 }
49
50 this.processDispatchResult(processedRequest, response, mappedHandler, err, dispatchException);
51 } catch (Exception var20) {
52 this.triggerAfterCompletion(processedRequest, response, mappedHandler, var20);
53 } catch (Error var21) {
54 this.triggerAfterCompletionWithError(processedRequest, response, mappedHandler, var21);
55 }
56
57 } finally {
58 if(asyncManager.isConcurrentHandlingStarted()) {
59 if(mappedHandler != null) {
60 mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
61 }
62 } else if(multipartRequestParsed) {
63 this.cleanupMultipart(processedRequest);
64 }
65
66 }
67 }
68
这个方法里面很多内容不需要关注，需要关注的的我讲讲
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2 //接收请求
3 HandlerExecutionChain mappedHandler = null;
4 //处理器执行链
5 boolean multipartRequestParsed = false;
6 //多部分请求，文件上传
7 WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
8 //异部请求
9
10 try {
11 try {
12
13 ModelAndView err = null;
14 //视图解析
15
16 try {
17
18 processedRequest = this.checkMultipart(request);
19 //检查是否是多部分请求
20 multipartRequestParsed = processedRequest != request;
21
22 mappedHandler = this.getHandler(processedRequest);
23 //这就返回处理器执行链
24
3.到这儿，点击getHandler（processedRequest）查看
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2 Iterator var2 = this.handlerMappings.iterator();
3
4 HandlerExecutionChain handler;
5 do {
6 if(!var2.hasNext()) {
7 return null;
8 }
9
10 HandlerMapping hm = (HandlerMapping)var2.next();
11 if(this.logger.isTraceEnabled()) {
12 this.logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name \'" + this.getServletName() + "\'");
13 }
14
15 handler = hm.getHandler(request);
16 } while(handler == null);
17
18 return handler;
19 }
20
我把关键代码提炼出来解释一波
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2 Iterator var2 = this.handlerMappings.iterator();
3 //处理器执行链
4 HandlerExecutionChain handler;
5 do {
6 if(!var2.hasNext()) {
7 return null;
8 }
9 //处理器映射器
10 HandlerMapping hm = (HandlerMapping)var2.next();
11
12 //继续追踪
13 handler = hm.getHandler(request);
14 } while(handler == null);
15
16 return handler;
17
**4.追踪hm.getHandler(request)方法，发现他是HandlerMapping接口的，（Ctrl+H）找它的实现类AbstractHandlerMapping,ctrl+F找getHandler
**
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2 Object handler = this.getHandlerInternal(request);
3 if(handler == null) {
4 handler = this.getDefaultHandler();
5 }
6
7 if(handler == null) {
8 return null;
9 } else {
10 if(handler instanceof String) {
11 String executionChain = (String)handler;
12 handler = this.getApplicationContext().getBean(executionChain);
13 }
14
15 HandlerExecutionChain executionChain1 = this.getHandlerExecutionChain(handler, request);
16 if(CorsUtils.isCorsRequest(request)) {
17 CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
18 CorsConfiguration handlerConfig = this.getCorsConfiguration(handler, request);
19 CorsConfiguration config = globalConfig != null?globalConfig.combine(handlerConfig):handlerConfig;
20 executionChain1 = this.getCorsHandlerExecutionChain(request, executionChain1, config);
21 }
22
23 return executionChain1;
24 }
25 }
26
同样，我把关键代码提出来解释一波
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2 Object handler = this.getHandlerInternal(request);
3 //处理器为空就用默认的
4 if(handler == null) {
5 handler = this.getDefaultHandler();
6 }
7 //默认的也是空就返回null
8 if(handler == null) {
9 return null;
10 } else {
11 //判断是否是String类型
12 if(handler instanceof String) {
13 //这儿就是我们一般用的处理器的从配置文件bean的id
14 String handlerName = (String)handler; // /hello
15 //这就是Spring啊
16 handler = this.getApplicationContext().getBean(handlerName);
17 }
18 //获取处理程序执行链
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3return this.getHandlerExecutionChain(handler, request); }
4
5.追踪获取程序执行链,this.getHandlerExecutionChain(handler,request)
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2 //三元表达式，是处理器执行链就强转，不是就获取根据处理器生成一个
3 HandlerExecutionChain chain = handler instanceof HandlerExecutionChain?(HandlerExecutionChain)handler:new HandlerExecutionChain(handler);
4 String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
5 Iterator var5 = this.adaptedInterceptors.iterator();
6
7 while(var5.hasNext()) {
8
9 //只需要知道这儿添加拦截器即可
10 HandlerInterceptor interceptor = (HandlerInterceptor)var5.next();
11 if(interceptor instanceof MappedInterceptor) {
12 MappedInterceptor mappedInterceptor = (MappedInterceptor)interceptor;
13 if(mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
14 chain.addInterceptor(mappedInterceptor.getInterceptor());
15 }
16 } else {
17 chain.addInterceptor(interceptor);
18 }
19 }
20
21 return chain;
22 }
23
