Spring MVC

Spring MVC流程

1. 用户发起请求到DispathcherServlet(中央调度器)
2. 中央调度器接收倒请求后调用handlerMapping映射器，handlerMapping通过url获取HandlerExecutionChain对象，里面包含了handler(handdlerMethod Controller的方法)、handlerInterceptor;
3. 中央调度器调用handlerAdapter,通过适配器模式获取适应的处理器，执行不同的handler(执行Controller的方法);
4. handler执行完给handlerAdapter返回 ModelAndView;
5. handlerAdapter将ModelAndView返回给 中央调度器  ;
6. 中央调度器  将ModelAndView给ViewResloer进行视图解析;
7. ViewResloer将解析后的View返回给中央调度器;
8. 中央调度器将model填充到View中进行视图渲染，然后返回给用户;
   

• DispatcherServlet:中央调度器, 接受请求，响应结果，作为其他组件的转发者，降低其他组件的耦合度;
• HandlerMapping:处理器映射器, 根据url去获取handler(可以理解为通过url获取指定Controller的Method);
• HandlerAdapter:处理器 ,基础的有RequestMappingHandlerAdapter(执行@RequestMapping的修饰的方法),HandlerFunctionAdapter(用于处理实现HandlerFunction接口的实现类),HttpRequestHandlerAdapter(用于处理实现HttpRequestHandler接口的实现类,大多数用于静态资源),SimpleControllerAdapter(用于处理实现HttpRequestHandler接口的实现类)；
  
• ViewResolver:视图解析器 ,根据逻辑视图名解析成真正的视图;

组件

• handlerMapping:根据url找到响应的处理器，常用的是找到Method
• handlerAdapter:找到handler适合的类型，并执行handler
• handlerExceptionResolver：处理handler产生的异常
• requestToViewNameTranslator:当ModelAndView对象不为空且里面的属性为空才会生效，默认返回请求路径的viewName
• ViewResolver:视图解析器，将viewName解析为真正的view视图
• LocaleResolver：解析出用户的区域
• theseResolver:主题，一个主题对应一个properties文件，里面包含图片、颜色、css样式等;
• multipartResolver:将文件包装恒Multipart
• flashMapManager:用于重定向 Redirect 时的参数数据传递

源码解析

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 {

                                //检查是否为文件
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				//获取到handler (获取到controller的方法 handlerMethod)
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				//根据handler获取指定的HandlerAdapter
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
                                //是否直接用客户端的缓存    
				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;
					}
				}

                                //在业务处理前调用拦截器的preHandle方法
    				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				// Actually invoke the handler.
                                //调用handler方法 (controller的方法) 如果是前后端分离 则此处会返回null
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

                                //当ModelAndView对象存在但对象内的view属性不存在则默认返回请求路径的viewName
				applyDefaultViewName(processedRequest, mv);

                                //业务处理后调用拦截器的postHandle方法
				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);
			}

                        //将model数据填充到view里面，并执行拦截器的afterCompletion方法
			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);
				}
			}
		}
	}