Spring MVC 源码分析 之 DispatcherServlet

	@Override
	public final void init() throws ServletException {

		// Set bean properties from init parameters.
		PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
		if (!pvs.isEmpty()) {
			try {
				BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
				ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
				bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
				initBeanWrapper(bw);
				bw.setPropertyValues(pvs, true);
			}
			catch (BeansException ex) {
				if (logger.isErrorEnabled()) {
					logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
				}
				throw ex;
			}
		}

		// Let subclasses do whatever initialization they like.
		initServletBean();
	}

	@Override
	protected final void initServletBean() throws ServletException {
		getServletContext().log("Initializing Spring " + getClass().getSimpleName() + " '" + getServletName() + "'");
		if (logger.isInfoEnabled()) {
			logger.info("Initializing Servlet '" + getServletName() + "'");
		}
		long startTime = System.currentTimeMillis();

		try {
			this.webApplicationContext = initWebApplicationContext();
			initFrameworkServlet();
		}
		catch (ServletException | RuntimeException ex) {
			logger.error("Context initialization failed", ex);
			throw ex;
		}

		if (logger.isDebugEnabled()) {
			String value = this.enableLoggingRequestDetails ?
					"shown which may lead to unsafe logging of potentially sensitive data" :
					"masked to prevent unsafe logging of potentially sensitive data";
			logger.debug("enableLoggingRequestDetails='" + this.enableLoggingRequestDetails +
					"': request parameters and headers will be " + value);
		}

		if (logger.isInfoEnabled()) {
			logger.info("Completed initialization in " + (System.currentTimeMillis() - startTime) + " ms");
		}
	}

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、调用 {@link MultipartResolver#isMultipart(HttpServletRequest)}方法检测请求是否是文件上传，
             * 如果是，则调用 {@link MultipartResolver#resolveMultipart(HttpServletRequest)} 对请求进行解析
             */
            processedRequest = checkMultipart(request);
            multipartRequestParsed = (processedRequest != request);

            // Determine handler for the current request.
            /**
             * 2、逐个调用 {@link HandlerMapping#getHandler(HttpServletRequest)}方法，以获取 {@link HandlerExecutionChain}对象实例
             */
            mappedHandler = getHandler(processedRequest);
            if (mappedHandler == null) {
                noHandlerFound(processedRequest, response);
                return;
            }

            // Determine handler adapter for the current request.
            /**
             * 3、逐个调用 {@link HandlerAdapter#supports(Object)}}方法，找到第一个支持处理 Handler 的 {@link HandlerAdapter}
             */
            HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

            // Process last-modified header, if supported by the handler.
            String method = request.getMethod();
            boolean isGet = "GET".equals(method);
            /**
             * 4、处理 GET｜HEAD 请求中的 last-modified 请求头
             */
            if (isGet || "HEAD".equals(method)) {
                long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                    return;
                }
            }

            /**
             * 5、触发拦截器 {@link HandlerInterceptor#preHandle(HttpServletRequest, HttpServletResponse, Object) }方法
             */
            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }

            // Actually invoke the handler.
            /**
             * 6、调用 {@link HandlerAdapter#handle(HttpServletRequest, HttpServletResponse, Object)}方法真实处理 {@code handler}
             */
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

            if (asyncManager.isConcurrentHandlingStarted()) {
                return;
            }
            /**
             * 7、从 Request 翻译视图名称 {@link RequestToViewNameTranslator#getViewName(HttpServletRequest)}
             */
            applyDefaultViewName(processedRequest, mv);
            /**
             * 8、触发拦截器的 {@link HandlerInterceptor#postHandle(HttpServletRequest, HttpServletResponse, Object, ModelAndView)} 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);
        }
        /**
         * 9、处理 DispatchResult
         */
        processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    } catch (Exception ex) {
        /**
         * 10、触发 {@link HandlerInterceptor#afterCompletion(HttpServletRequest, HttpServletResponse, Object, Exception)}方法
         */
        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) {
                /**
                 * 11、触发 {@link AsyncHandlerInterceptor#afterConcurrentHandlingStarted(HttpServletRequest, HttpServletResponse, Object)}方法
                 */
                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            }
        } else {
            // Clean up any resources used by a multipart request.
            /**
             * 12、如果是文件上传请求，则清理 {@link MultipartResolver#cleanupMultipart(MultipartHttpServletRequest)}
             */
            if (multipartRequestParsed) {
                cleanupMultipart(processedRequest);
            }
        }
    }
}