SpringMVC源码-DispatcherServlet处理请求概述

请求由Servlet的doService处理。

DispatcherServlet.doService(HttpServletRequest request, HttpServletResponse response)

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
	logRequest(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);
	}

	RequestPath previousRequestPath = null;
	if (this.parseRequestPath) {
		previousRequestPath = (RequestPath) request.getAttribute(ServletRequestPathUtils.PATH_ATTRIBUTE);
		ServletRequestPathUtils.parseAndCache(request);
	}

	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);
			}
		}
		ServletRequestPathUtils.setParsedRequestPath(previousRequestPath, request);
	}
}

1、logRequest返回request的参数字符串供日志打印。
2、对request的属性做快照
3、request设置属性WEB_APPLICATION_CONTEXT_ATTRIBUTE为WebApplicationContext，设置属性LOCALE_RESOLVER_ATTRIBUTE为localeResolver，设置属性THEME_RESOLVER_ATTRIBUTE为themeResolver，设置属性THEME_SOURCE_ATTRIBUTE为ThemeSource。
4、如果flashMapManager不为null，flashMapManager.retrieveAndUpdate保存以前的FlashMap，匹配当前请求的FlashMap并返回，inputFlashMap不为null设置INPUT_FLASH_MAP_ATTRIBUTE为名，inputFlashMap为值的属性。设置OUTPUT_FLASH_MAP_ATTRIBUTE和FLASH_MAP_MANAGER_ATTRIBUTE属性。
5、如果parseRequestPath为true，解析request的PATH_ATTRIBUTE属性值并缓存。
6、doDispatch分发请求进行处理
7、还原request的属性快照

DispatcherServlet.doDispatch(HttpServletRequest request, HttpServletResponse response)

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 {
			processedRequest = checkMultipart(request);
			multipartRequestParsed = (processedRequest != request);

			// Determine handler for the current request.
			mappedHandler = getHandler(processedRequest);
			if (mappedHandler == null) {
				noHandlerFound(processedRequest, response);
				return;
			}

			// Determine handler adapter for the current request.
			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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
					return;
				}
			}

			if (!mappedHandler.applyPreHandle(processedRequest, response)) {
				return;
			}

			// Actually invoke the handler.
			mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

			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) {
				mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
			}
		}
		else {
			// Clean up any resources used by a multipart request.
			if (multipartRequestParsed) {
				cleanupMultipart(processedRequest);
			}
		}
	}
}

1、WebAsyncUtils.getAsyncManager获取异步web管理器WebAsyncManager
2、checkMultipart检查是否是文件上传请求
3、调用getHandler获取request的handle
4、如果没有当前请求的handle则调用noHandlerFound
5、调用getHandlerAdapter获取handle对应的HandlerAdapter
6、如果请求类型是GET或HEAD则检查请求的lastModified
7、调用mappedHandler.applyPreHandle处理拦截器的前置方法HandlerInterceptor.preHandle,如果为false则退出
8、HandlerAdapter.handle调用Controller层的方法处理请求并返回ModelAndView
9、applyDefaultViewName处理视图名
10、mappedHandler.applyPostHandle处理拦截器的前置方法HandlerInterceptor.postHandle
11、processDispatchResult渲染视图
12、如果是异步web调用mappedHandler.applyAfterConcurrentHandlingStarted否则cleanupMultipart清理文件上传请求

DispatcherServlet.checkMultipart(HttpServletRequest request)

protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
	if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
		if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
			if (DispatcherType.REQUEST.equals(request.getDispatcherType())) {
				logger.trace("Request already resolved to MultipartHttpServletRequest, e.g. by MultipartFilter");
			}
		}
		else if (hasMultipartException(request)) {
			logger.debug("Multipart resolution previously failed for current request - " +
					"skipping re-resolution for undisturbed error rendering");
		}
		else {
			try {
				return this.multipartResolver.resolveMultipart(request);
			}
			catch (MultipartException ex) {
				if (request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) != null) {
					logger.debug("Multipart resolution failed for error dispatch", ex);
					// Keep processing error dispatch with regular request handle below
				}
				else {
					throw ex;
				}
			}
		}
	}
	// If not returned before: return original request.
	return request;
}

如果multipartResolver不为null且multipartResolver.isMultipart判断request是文件上传请求则
1、WebUtils.getNativeRequest判断request是MultipartHttpServletRequest，若是且request.getDispatcherType()是DispatcherType.REQUEST打印日志
2、hasMultipartException判断是否有异常，若有打印日志
3、调用multipartResolver.resolveMultipart解析request并返回