SpringMVC工作原理之：HandlerAdapter

根据 Handler 来找到支持它的 HandlerAdapter，通过 HandlerAdapter 执行这个 Handler 得到 ModelAndView 对象。HandlerAdapter 接口中的方法如下：

supports(Object handler); // 当前 HandlerAdapter 是否支持这个 Handler

handle(HttpServletRequest req, HttpServletResponse res, Object handler); // 利用 Handler 处理请求

getLastModified(HttpServletRequest request, Object handler);

1 RequestMappingHandlerAdapter

从上面的文章中可以知道，利用 RequestMappingHandlerMapping 获取的 Handler 是 HadnlerMethod 类型，它代表 Controller 里要执行的方法，而 RequestMappingHandlerAdapter 可以执行 HadnlerMethod 对象。

RequestMappingHandlerAdapter 的 handle() 方法是在它的父类 AbstractHandlerMethodAdapter 类中实现的，源码如下所示

handleInternal() 方法是由 RequestMappingHandlerAdapter 自己来实现的，源码如下所示

@Override
	protected final ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
        // 是否通过 @SessionAttributes 注释声明了 session 属性。
		if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
			// Always prevent caching in case of session attribute management.
			checkAndPrepare(request, response, this.cacheSecondsForSessionAttributeHandlers, true);
		}
		else {
			// Uses configured default cacheSeconds setting.
			checkAndPrepare(request, response, true);
		}

		// 是否需要在 synchronize 块中执行
		if (this.synchronizeOnSession) {
			HttpSession session = request.getSession(false);
			if (session != null) {
				Object mutex = WebUtils.getSessionMutex(session);
				synchronized (mutex) {
                    // 执行 HandlerMethod
					return invokeHandleMethod(request, response, handlerMethod);
				}
			}
		}
        // 执行 HandlerMethod，得到 ModelAndView
		return invokeHandleMethod(request, response, handlerMethod);
	}

继续再来看一下如何得到 ModelAndView，invokeHandlerMethod() 方法如下

private ModelAndView invokeHandleMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
        // 数据绑定
		WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
		ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
         // 绑定参数，执行方法
		ServletInvocableHandlerMethod requestMappingMethod = createRequestMappingMethod(handlerMethod, binderFactory);
        // 创建模型和视图容器
		ModelAndViewContainer mavContainer = new ModelAndViewContainer();
        // 设置FlasgMap中的值
		mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
         // 初始化模型
		modelFactory.initModel(webRequest, mavContainer, requestMappingMethod);
		mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

		AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
		asyncWebRequest.setTimeout(this.asyncRequestTimeout);

		final WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
		asyncManager.setTaskExecutor(this.taskExecutor);
		asyncManager.setAsyncWebRequest(asyncWebRequest);
		asyncManager.registerCallableInterceptors(this.callableInterceptors);
		asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);

		if (asyncManager.hasConcurrentResult()) {
			Object result = asyncManager.getConcurrentResult();
			mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
			asyncManager.clearConcurrentResult();

			if (logger.isDebugEnabled()) {
				logger.debug("Found concurrent result value [" + result + "]");
			}
			requestMappingMethod = requestMappingMethod.wrapConcurrentResult(result);
		}

		requestMappingMethod.invokeAndHandle(webRequest, mavContainer);

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

		return getModelAndView(mavContainer, modelFactory, webRequest);
	}

2 HttpRequestHandlerAdapter

HttpRequestHandlerAdapter 可以执行 HttpRequestHandler 类型的 Handler，源码如下

3 SimpleControllerHandlerAdapter

SimpleControllerHandlerAdapter 可以执行 Controller 类型的 Handler，源码如下

4 SimpleServletHandlerAdapter 

SimpleServletHandlerAdapter 可以执行 Servlet 类型的 Handler，源码如下