springmvc揭秘异常处理机制

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HandlerExceptionResolver异常处理

HandlerExceptionResolver是专门进行异常处理的，在render之前进行工作，从异常中解析出ModelAndView

public interface HandlerExceptionResolver {
  
   ModelAndView resolveException(
         HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex);

}

• DefaultHandlerExceptionResolver 根据不同类型的异常来进行解析，response.sendError设置不同的错误码

  response.sendError(HttpServletResponse.SC_NOT_FOUND);
  

• ExceptionHandlerExceptionResolver 使用@ExceptionHandler注解的方法来进行异常解析

• ResponseStatusExceptionResolver 解析有@ResponseStatus注解的异常

• SimpleMappingExceptionResolver 通过配置的异常类和View的映射关系来解析异常

ExceptionHandlerExceptionResolver

我一般都是使用@ExceptionHandler注解，所以就以ExceptionHandlerExceptionResolver为例

所有的HandlerExceptionResolver实现类都是去重写resolveException方法

// org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver#resolveException
@Override
public ModelAndView resolveException(
      HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
		// 判断当前HandlerExceptionResolver是否可以解析
   if (shouldApplyTo(request, handler)) {
     // 判断是否禁用缓存，如果禁用缓存的话，设置响应头
      prepareResponse(ex, response);
     // 具体的处理逻辑
      ModelAndView result = doResolveException(request, response, handler, ex);
      if (result != null) {
         
         // Explicitly configured warn logger in logException method.
         logException(ex, request);
      }
      return result;
   }
   else {
      return null;
   }
}

shouldApplyTo

// org.springframework.web.servlet.handler.AbstractHandlerMethodExceptionResolver#shouldApplyTo
@Override
protected boolean shouldApplyTo(HttpServletRequest request, Object handler) {
   if (handler == null) {
      return super.shouldApplyTo(request, handler);
   }
   else if (handler instanceof HandlerMethod) {
      HandlerMethod handlerMethod = (HandlerMethod) handler;
      handler = handlerMethod.getBean();
      return super.shouldApplyTo(request, handler);
   }
   else {
      return false;
   }
}

// org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver#shouldApplyTo
protected boolean shouldApplyTo(HttpServletRequest request, Object handler) {
		if (handler != null) {
      // mappedHandlers是处理器的集合
      if (this.mappedHandlers != null && this.mappedHandlers.contains(handler)) {
				return true;
			}
      // mappedHandlerClasses是处理器类型的集合
			if (this.mappedHandlerClasses != null) {
				for (Class<?> handlerClass : this.mappedHandlerClasses) {
					if (handlerClass.isInstance(handler)) {
						return true;
					}
				}
			}
		}
		// Else only apply if there are no explicit handler mappings.
		return (this.mappedHandlers == null && this.mappedHandlerClasses == null);
	}

doResolveException

该方法是处理异常的实际方法

protected final ModelAndView doResolveException(
      HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {

   return doResolveHandlerMethodException(request, response, (HandlerMethod) handler, ex);
}

protected ModelAndView doResolveHandlerMethodException(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod, Exception exception) {
		// 找到处理异常的方法
		ServletInvocableHandlerMethod exceptionHandlerMethod = getExceptionHandlerMethod(handlerMethod, exception);
		if (exceptionHandlerMethod == null) {
			return null;
		}
		// 设置argumentResolvers和returnValueHandlers
		exceptionHandlerMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
		exceptionHandlerMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		ModelAndViewContainer mavContainer = new ModelAndViewContainer();

		try {
			
			Throwable cause = exception.getCause();
			if (cause != null) {
				// Expose cause as provided argument as well
        // 执行exceptionHandler方法解析异常
				exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, cause, handlerMethod);
			}
			else {
				// Otherwise, just the given exception as-is
				exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, handlerMethod);
			}
		}
		catch (Throwable invocationEx) {
			
			// Continue with default processing of the original exception...
			return null;
		}

		if (mavContainer.isRequestHandled()) {
			return new ModelAndView();
		}
		else {
			ModelMap model = mavContainer.getModel();
			HttpStatus status = mavContainer.getStatus();
			ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, status);
			mav.setViewName(mavContainer.getViewName());
			if (!mavContainer.isViewReference()) {
				mav.setView((View) mavContainer.getView());
			}
			if (model instanceof RedirectAttributes) {
				Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
				RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
			}
			return mav;
		}
	}

参考文献

• HandlerExceptionResolver