SpringMVC源碼解析二：請求處理過程1

DispatcherServlet繼承了FrameworkServlet，請求首先進入FrameworkServlet的service方法：

FrameworkServlet類中：
protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
		if (HttpMethod.PATCH == httpMethod || httpMethod == null) {
			processRequest(request, response);
		}
		else {
			super.service(request, response);
		}
	}
	
	
	protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {

	long startTime = System.currentTimeMillis();
	Throwable failureCause = null;

	LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
	LocaleContext localeContext = buildLocaleContext(request);

	RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
	ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

	WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
	asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());

	initContextHolders(request, localeContext, requestAttributes);

	try {
		doService(request, response);
	}
	catch (ServletException | IOException ex) {
		failureCause = ex;
		throw ex;
	}
	catch (Throwable ex) {
		failureCause = ex;
		throw new NestedServletException("Request processing failed", ex);
	}

	finally {
		resetContextHolders(request, previousLocaleContext, previousAttributes);
		if (requestAttributes != null) {
			requestAttributes.requestCompleted();
		}

		if (logger.isDebugEnabled()) {
			if (failureCause != null) {
				this.logger.debug("Could not complete request", failureCause);
			}
			else {
				if (asyncManager.isConcurrentHandlingStarted()) {
					logger.debug("Leaving response open for concurrent processing");
				}
				else {
					this.logger.debug("Successfully completed request");
				}
			}
		}

		publishRequestHandledEvent(request, response, startTime, failureCause);
	}
	
}

DispatcherServlet 類中:
	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		if (logger.isDebugEnabled()) {
			String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
			logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
					" processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
		}

		// Keep a snapshot of the request attributes in case of an include,
		// to be able to restore the original attributes after the include.
		Map<String, Object> attributesSnapshot = null;
		if (WebUtils.isIncludeRequest(request)) {
			attributesSnapshot = new HashMap<>();
			Enumeration<?> attrNames = request.getAttributeNames();
			while (attrNames.hasMoreElements()) {
				String attrName = (String) attrNames.nextElement();
				if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
					attributesSnapshot.put(attrName, request.getAttribute(attrName));
				}
			}
		}

		// Make framework objects available to handlers and view objects.
		request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
		request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
		request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
		request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());

		if (this.flashMapManager != null) {
			FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
			if (inputFlashMap != null) {
				request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
			}
			request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
			request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
		}

		try {
			doDispatch(request, response);
		}
		finally {
			if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
				// Restore the original attribute snapshot, in case of an include.
				if (attributesSnapshot != null) {
					restoreAttributesAfterInclude(request, attributesSnapshot);
				}
			}
		}
	}

下面就到了DispatcherServlet類的核心方法：doDispatch

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 {
				// 1.檢查是否是文件上傳的請求
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.
				// 2.取得處理當前請求的controller,這裏也稱爲hanlder,處理器,
				// 	 第一個步驟的意義就在這裏體現了.這裏並不是直接返回controller,
				//	 而是返回的HandlerExecutionChain請求處理器鏈對象,
				//	 該對象封裝了handler和interceptors.
				mappedHandler = getHandler(processedRequest);
				// 如果handler爲空,則返回404
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
				//3. 獲取處理request的處理器適配器handler adapter
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				// 處理 last-modified 請求頭
				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;
				}

				// Actually invoke the handler.
				// 4.實際的處理器處理請求,返回結果視圖對象
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

				//5. 結果視圖對象的處理
				applyDefaultViewName(processedRequest, mv);
				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);
			}
			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) {
					// 請求成功響應之後的方法
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}
	}

 

此方法中最重要的就是以下幾個步驟：

2.取得處理當前請求的controller,這裏也稱爲hanlder,處理器,

mappedHandler = getHandler(processedRequest);

3. 獲取處理request的處理器適配器handler adapter
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

4.實際的處理器處理請求,返回結果視圖對象
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

5.結果視圖對象的處理
 applyDefaultViewName(processedRequest, mv);
 mappedHandler.applyPostHandle(processedRequest, response, mv);

具體處理方法後面會具體介紹