SpringMVC 工作流程

官方文档

最好的文档当然是我们的官网文档了
官网文档

小知识

在了解SpringMVC的工作流程之前先恶补一下小知识
（1）DispatcherServlet: 前置控制器，相当于一个调度器。
（2）HandlerMapping: 处理器映射器，根据配置和注解或者名字找到最终要执行的Controller
（3）HandlerAdapter:处理器的适配器,处理handler
（4）Handler:处理器，可以称作后置控制器。在使用中一般用controller表示
（5）ViewResolver：视图解析器，把从handler返回的逻辑view转化成真实的view

流程图

流程图是网上随便找的，自己画的太不忍直视了。

源码解读

我们可以根据源码一起验证我们的工作流程图
查看 org.springframework.web.servlet.DispatcherServlet类中的doDispatch方法

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        //请求进入DispatcherServlet
        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;

                // Determine handler for the current request.
                //DispatcherServlet调用HandleMapping获取HandlerExecutionChain处理链
                mappedHandler = getHandler(processedRequest, false);
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
                // 把HandlerMapping返回的处理链对象调用getHandler()方法获得handler，并且传送给HandlerAdapter
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (logger.isDebugEnabled()) {
                        logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                    }
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }

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

                try {
                    // Actually invoke the handler.
                   //handlerAdpter处理handler，并且返回ModelAndView
                    mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
                }
                finally {
                    if (asyncManager.isConcurrentHandlingStarted()) {
                        return;
                    }
                }

                applyDefaultViewName(request, mv);
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                dispatchException = ex;
            }
            // 解析视图，并且处理异常。在源码中找到该方法，追溯下去，可以看到我们的ViewResolver类
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Error err) {
            triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
        }
        finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                // Instead of postHandle and afterCompletion
                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                return;
            }
            // Clean up any resources used by a multipart request.
            if (multipartRequestParsed) {
                cleanupMultipart(processedRequest);
            }
        }
    }

源码中我加了工作流程中重要步骤的注解，通过上面的源码，我们可以和我们的流程图一一对应起来。这样是不是就比较容易理解了呢。当然这只是工作流程的一个简单描述，其实内部还有很多复杂的实现，革命还未成功，同志还需努力。

转载于:https://www.cnblogs.com/amberbar/p/10065013.html