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————-********
先放一张图
很熟悉啊，之前就看过，我们之前已经把handlerMapping剖了个底朝天，顺着上次的进度，继续跟，把HandlerAdapter处理器适配器剖一下
它同样是由中央调度器DispatcherServlet调度到的，所以，还是这个类中找doDispatch(request,response)这个方法，我把有用的代码，扒下来
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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;
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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//上面的是我说的HandleMapping的执行 流程
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23//所以从后面的第一行开始看
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27 HandlerAdapter ex = this.getHandlerAdapter(mappedHandler.getHandler());
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2它外面的this.getHandlerAdpter
3点过去追踪
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2//迭代器
3 Iterator var2 = this.handlerAdapters.iterator();
4//一会要返回去的适配器对象
5 HandlerAdapter ha;
6 do {
7//如果没有下一个的话。就抛异常
8 if(!var2.hasNext()) {
9 throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
10 }
11//将此强转成为处理器适配器
12 ha = (HandlerAdapter)var2.next();
13 if(this.logger.isTraceEnabled()) {
14 this.logger.trace("Testing handler adapter [" + ha + "]");
15 }
16 } while(!ha.supports(handler));
17//这儿有个适配器模式
18 return ha;
19 }
20
这是下载源码后的最直观的源码
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2 for (HandlerAdapter ha : this.handlerAdapters) {
3 if (logger.isTraceEnabled()) {
4 logger.trace("Testing handler adapter [" + ha + "]");
5 }
6 if (ha.supports(handler)) {
7 return ha;
8 }
9 }
10 throw new ServletException("No adapter for handler [" + handler +
11 "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
12 }
13
看ha.sipports(handler)这个方法
找到HandlerAdapter接口
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3 boolean supports(Object handler);
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5 ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
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7 long getLastModified(HttpServletRequest request, Object handler);
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9}
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再来看一下自己写的控制器实现了Controller。这样就看DispatcherServlet属性中的HandlerApater谁支持Controller类型的处理器了。在运行的过程中发现SimpleControllerHandlerAdapter是支持Controller类型的控制器的。
来看一下SimpleControllerHandlerAdapter的代码
找它的实现类：Ctrl+H SimpleControllerHandlerAdapter
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3 public boolean supports(Object handler) {
4 return (handler instanceof Controller);
5 }
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7 public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
8 throws Exception {
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10 return ((Controller) handler).handleRequest(request, response);
11 }
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13 public long getLastModified(HttpServletRequest request, Object handler) {
14 if (handler instanceof LastModified) {
15 return ((LastModified) handler).getLastModified(request);
16 }
17 return -1L;
18 }
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20}
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它support来判断是否是处理器
拿到处理器在中央调度器一处调用了handle方法
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2 HttpServletRequest processedRequest = request;
3 HandlerExecutionChain mappedHandler = null;
4 boolean multipartRequestParsed = false;
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6 WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
7
8 try {
9 ModelAndView mv = null;
10 Exception dispatchException = null;
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12 try {
13 processedRequest = checkMultipart(request);
14 multipartRequestParsed = (processedRequest != request);
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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 }
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23 // Determine handler adapter for the current request.
24 HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
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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 }
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39 if (!mappedHandler.applyPreHandle(processedRequest, response)) {
40 return;
41 }
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43 // Actually invoke the handler.
44 mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
45
46//就是上面这处
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看看handle方法,因为被执行调用到，它返回ModelAndView
里面return走的handleRequest是Controller接口的，找它的实现类
AbstractController抽象类，它有实现handleRequest
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2 public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
3 throws Exception {
4
5 // Delegate to WebContentGenerator for checking and preparing.
6 checkRequest(request);
7 prepareResponse(response);
8
9 // Execute handleRequestInternal in synchronized block if required.
10 if (this.synchronizeOnSession) {
11 HttpSession session = request.getSession(false);
12 if (session != null) {
13 Object mutex = WebUtils.getSessionMutex(session);
14 synchronized (mutex) {
15 return handleRequestInternal(request, response);
16 }
17 }
18 }
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20 return handleRequestInternal(request, response);
21 }
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看到最后面的那个返回值了吗？是ModelAndView对象，它调用了handleRequestInternal(request,respone)这个方法
还记得AbstractController的实现类吗？不是有种处理器的定义方法就是继承AbstractController****
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3import org.springframework.web.servlet.ModelAndView;
4import org.springframework.web.servlet.mvc.AbstractController;
5import org.springframework.web.servlet.mvc.Controller;
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7import javax.servlet.http.HttpServletRequest;
8import javax.servlet.http.HttpServletResponse;
9
10/**
11 * Created by Dawn on 2018/3/19.
12 */
13//处理器
14public class FirstController extends AbstractController {
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16 protected ModelAndView handleRequestInternal(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
17 ModelAndView me=new ModelAndView();
18 me.setViewName("index");
19 return me;
20 }
21}
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它的实现类默认要求必须实现handleRequestInternal（request,response）这个方法
所以，理清了吧，再一步步return回去，最后回到了中央调度器
结论，中央处理器DispatcherServlet通过处理器执行链找到handlerAdapter处理器适配器，后者调度了它的处理器，通过处理器处理，返回一个ModelAndView模型和视图对象，一路返回，到中央调度器
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