/**
     * 此方法定義一個(gè)異常處理器，僅僅處理異常 DemoException , 它使用一個(gè)視圖對(duì)象 
     * DemoExceptionHandlerView 來(lái)處理異常 
     * @param e
     * @return
     */
    @ExceptionHandler(DemoException.class)
    public View handleDemoException(DemoException e) {
        return new DemoExceptionHandlerView(e);
    }

    // DispatcherServlet 代碼片段，
    // 在 HandlerAdaptor 執(zhí)行 Handler 之后調(diào)用，
    // 如果之前的邏輯有異常，則 exception 不為 null，
    // 如果之前的邏輯執(zhí)行正常， 則 exception 為 null
	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {
		boolean errorView = false;
		if (exception != null) {
           // 請(qǐng)求處理出現(xiàn)了異常 
			if (exception instanceof ModelAndViewDefiningException) {
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = ((ModelAndViewDefiningException) exception).getModelAndView();
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
              // 這里視圖處理該異常：
              // 1. 內(nèi)部將其完全處理
              // 2. 或者返回一個(gè)用于渲染錯(cuò)誤的數(shù)據(jù)模型和視圖
				mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}
        // ... 省略其他代碼
    }        
	@Nullable
	protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
			@Nullable Object handler, Exception ex) throws Exception {
		// Success and error responses may use different content types
		request.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
		// Check registered HandlerExceptionResolvers...
		ModelAndView exMv = null;
		if (this.handlerExceptionResolvers != null) {
          // 遍歷`handlerExceptionResolvers`中每個(gè)`HandlerExceptionResolver`對(duì)象
          // 試圖對(duì)異常 ex 進(jìn)行處理
			for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {
				exMv = resolver.resolveException(request, response, handler, ex);
				if (exMv != null) {
					break;
				}
			}
		}
		if (exMv != null) {
			// ...
			return exMv;
		}
		throw ex;
	}