SpringMVC工作原理流程（二）

    public void service(ServletRequest req, ServletResponse res)
	throws ServletException, IOException
    {
	HttpServletRequest	request;
	HttpServletResponse	response;
	
	try {
	    request = (HttpServletRequest) req;
	    response = (HttpServletResponse) res;
	} catch (ClassCastException e) {
	    throw new ServletException("non-HTTP request or response");
	}
	//调用FrameworkServlet的Service方法
	service(request, response);
    }

 @Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
		if (HttpMethod.PATCH == httpMethod || httpMethod == null) {
			//统一处理请求
			processRequest(request, response);
		}
		else {
			//调用HttpServlet的service
			super.service(request, response);
		}
	}

protected void service(HttpServletRequest req, HttpServletResponse resp)
	throws ServletException, IOException
    {
	String method = req.getMethod();

	if (method.equals(METHOD_GET)) {
	    long lastModified = getLastModified(req);
	    if (lastModified == -1) {
		doGet(req, resp);
	    } else {
		long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
		if (ifModifiedSince < (lastModified / 1000 * 1000)) {
		    maybeSetLastModified(resp, lastModified);
		    doGet(req, resp);
		} else {
		    resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
		}
	    }

	} else if (method.equals(METHOD_HEAD)) {
	    long lastModified = getLastModified(req);
	    maybeSetLastModified(resp, lastModified);
	    doHead(req, resp);

	} else if (method.equals(METHOD_POST)) {
	    doPost(req, resp);
	    
	} else if (method.equals(METHOD_PUT)) {
	    doPut(req, resp);	
	    
	} else if (method.equals(METHOD_DELETE)) {
	    doDelete(req, resp);
	    
	} else if (method.equals(METHOD_OPTIONS)) {
	    doOptions(req,resp);
	    
	} else if (method.equals(METHOD_TRACE)) {
	    doTrace(req,resp);
	    
	} else {
	   	String errMsg = lStrings.getString("http.method_not_implemented");
	    Object[] errArgs = new Object[1];
	    errArgs[0] = method;
	    errMsg = MessageFormat.format(errMsg, errArgs);
	    
	    resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
	}
    }

	@Override
	protected final void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		processRequest(request, response);
	}

	protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		Throwable failureCause = null;
		//获取与当前线程绑定的localContext对象
		LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
		//构造新的LocaleContext
		LocaleContext localeContext = buildLocaleContext(request);
		//获取与当前线程绑定的RequestAttributes对象
		RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
		//构造新的LocaleContext
		ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
		asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
		//新构建的localeContext和requestAttributes与当前线程绑定，并且设置值
		initContextHolders(request, localeContext, requestAttributes);
		try {
			//抽象方法，具体实现在DispatherServlet
			doService(request, response);
		}
		catch (ServletException ex) {
			failureCause = ex;
			throw ex;
		}
		catch (IOException ex) {
			failureCause = ex;
			throw ex;
		}
		catch (Throwable ex) {
			failureCause = ex;
			throw new NestedServletException("Request processing failed", ex);
		}

		finally {
			//doService执行完之后，恢复原来的previousLocaleContext和previousAttributes
			resetContextHolders(request, previousLocaleContext, previousAttributes);
			if (requestAttributes != null) {
				//request已经执行完成，不可赋值
				requestAttributes.requestCompleted();
			}

			if (logger.isDebugEnabled()) {
				//省略日志
			}
			//无论请求是否成功，都会发布信息
			publishRequestHandledEvent(request, response, startTime, failureCause);
		}
	}

@Override
	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		//判断是否是include请求
		Map<String, Object> attributesSnapshot = null;
		if (WebUtils.isIncludeRequest(request)) {
			attributesSnapshot = new HashMap<String, Object>();
			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));
				}
			}
		}

		//设置属性
		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());

		//可以保存重定向数据
		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 {
			//进行分发处理
			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);
				}
			}
		}
	}

	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 {

				//检查是不是上传请求
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				//根据Request查找Handler
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null || mappedHandler.getHandler() == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				//根据Handler查找HandlerAdapter
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// 处理GET，HEAD请求的lastModified
				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;
					}
				}
				//执行相应Interceptor的preHandle
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				// HandlerAdapter使用Handler处理请求
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}
				//当view为空时，根据request设置默认view
				applyDefaultViewName(processedRequest, mv);
				//执行相应的Interceptor的postHandle
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
			catch (Throwable err) {
				//处理返回结果。包括处理异常、渲染页面、发出完成通知触发Interceptor的afterCompletion
				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) {
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				//删除上传请求资源
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}
	}