Spring - MVC执行流程

SpringMVC执行源代码

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 {
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);
                // 根据当前请求查找HandlerExecutionChain 
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null) {
                                          //没有找到直接返回no mapping错误
                    noHandlerFound(processedRequest, response);
                    return;
                }
                // Determine handler adapter for the current request.
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                                //进行请求方式检查
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }
                              //执行拦截器链的applyPreHandle
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }
                // Actually invoke the handler.
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }
                applyDefaultViewName(processedRequest, mv);
                              //执行拦截器链applyPostHandle
                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 NestedServletException("Handler dispatch failed", err);
            }
                        //视图渲染完成后执行拦截器链的triggerAfterCompletion
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                    new NestedServletException("Handler processing failed", 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);
                }
            }
        }
    }

SpringMVC执行流程:

1. 用户发送请求至前端控制器DispatcherServlet;
2. DispatcherServlet收到请求调用处理器映射器HandlerMapping;
3. 处理器映射器根据请求url找到具体的处理器，生成处理器执行链HandlerExecutionChain(包括处理器对象和处理器拦截器)一并返回给DispatcherServlet;
4. DispatcherServlet根据处理器Handler获取处理器适配器HandlerAdapter执行HandlerAdapter处理一系 列的操作，如：参数封装，数据格式转换，数据验证等操作;
5. 执行处理器Handler前置拦截器，handler和后置拦截器方法(Controller，也叫页面控制器);
6. Handler执行完成返回ModelAndView;
7. HandlerAdapter将Handler执行结果ModelAndView返回到DispatcherServlet;
8. DispatcherServlet将ModelAndView传给ViewReslover视图解析器;
9. ViewReslover解析后返回具体View;
10. DispatcherServlet对View进行渲染视图（即将模型数据model填充至视图中）然后写入response;
11. 执行HandlerExecutionChain的triggerAfterCompletion方法;
12. DispatcherServlet响应用户。