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。