调用顺序：

1. Filter.doFilter() (自定义Filter)

   1. //do something （处理请求）

   2. chain.doFilter()

      1. //...

      2. DispatcherServlet (所有请求都经过这个Servlet分发)

         1. Interceptor.preHandle()
         2. Controller
         3. Interceptor.postHandle
         4. @ExceptionHandler
         5. Interceptor.afterCompletion()

      3. //...

   3. do something （处理响应）

DispatcherServlet.doDispatch()

/**
 * 用于HTTP请求处理程序/控制器的中央分派器，例如用于web UI控制器或基于HTTP的远程服务导出器。
 * 分派给注册的处理程序以处理web请求，提供方便的映射和异常处理功能。
 */
public class DispatcherServlet extends FrameworkServlet {
    /**
     * 所有HTTP方法都由该方法处理。由HandlerAdapters或处理程序自己决定哪些方法是可接受的。 
     * 参数：request–当前HTTP请求 
     *      response–当前HTTP响应
     */
    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

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

            try {
                //根据content-type判断，是multipart类型且未解析，就解析并返回MultipartHttpServletRequest，否则返回原request
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // 确定当前请求的处理程序
                mappedHandler = getHandler(processedRequest);  // 图-mappedHandler
                if (mappedHandler == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // 确定当前请求的处理程序适配器。
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // 如果处理程序支持，则处理上次修改的报头。 
                String method = request.getMethod();
                boolean isGet = HttpMethod.GET.matches(method);
                if (isGet || HttpMethod.HEAD.matches(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }
                //调拦截器 Interceptor.preHandle
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // 实际上调用处理程序。
                 //调Controller
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                applyDefaultViewName(processedRequest, mv);
                 //调拦截器 Interceptor.postHandle
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                dispatchException = ex;
            }
            catch (Throwable err) {
                // As of 4.3, we're processing Errors thrown from handler methods as well,
                // making them available for @ExceptionHandler methods and other scenarios.
                dispatchException = new ServletException("Handler dispatch failed: " + err, err);
            }
             //调@ExceptionHandler
             //调拦截器 Interceptor.afterCompletion
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                    new ServletException("Handler processing failed: " + err, 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);
                }
            }
        }
    }
}