SpringMVC源码情操陶冶-AbstractHandlerExceptionResolver

springmvc支持服务端在处理业务逻辑过程中出现异常的时候可以配置相应的modelandview对象返回给客户端，本文介绍springmvc默认的几种handlerExceptionResolver类

springmvc的xml配置化-Exception配置

<bean id="exceptionHandler" class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver"> <!--设置默认返回viewName，通常与freemarker引擎搭配使用--> <property name="defaultErrorView" value="error/defaultError" /> <!--设置默认返回response status--> <property name="defaultStatusCode" value="500" /> <!--配置相应的异常类与viewName的映射--> <property name="exceptionMappings"> <props> <prop key="SessionTimeoutException">redirect:../login.html</prop> <prop key="AuthenticationException">error/403</prop> </props> </property> </bean> 

以上的配置会对出SessionTimeoutException异常则跳转至login页面，对AuthenticationException异常则跳转至403页面，对其他的异常则默认跳转至defaultError页面呈现并返回500的错误码

接口内只有一个方法resolveException()，通过解析异常查询配置以得到符合条件的ModelAndView对象

 /** * Try to resolve the given exception that got thrown during handler execution, * returning a {@link ModelAndView} that represents a specific error page if appropriate. * <p>The returned {@code ModelAndView} may be {@linkplain ModelAndView#isEmpty() empty} * to indicate that the exception has been resolved successfully but that no view * should be rendered, for instance by setting a status code. * @param request current HTTP request * @param response current HTTP response * @param handler the executed handler, or {@code null} if none chosen at the * time of the exception (for example, if multipart resolution failed) * @param ex the exception that got thrown during handler execution * @return a corresponding {@code ModelAndView} to forward to, or {@code null} * for default processing */ ModelAndView resolveException( HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex); 

所有的spring内置异常解析类都继承于此，直奔主题看resolveException()方法

 @Override public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) { //判断是否需要解析 if (shouldApplyTo(request, handler)) { //此处一般是判断内部属性preventResponseCaching是否为true，是则设置响应包头cache-control:no-store prepareResponse(ex, response); //使用模板方法doResolveException()方法供子类实现 ModelAndView result = doResolveException(request, response, handler, ex); if (result != null) { //日志打印一发 logException(ex, request); } return result; } else { return null; } } 

附带着分析下shouldApplyTo()方法

 /** **可以配置mappedHandlers和mappedHandlerClasses属性来特定匹配 **默认情况下两者都为空则直接返回true，表明对所有的handler都进行异常解析 */ protected boolean shouldApplyTo(HttpServletRequest request, Object handler) { //此处的handler一般为bean对象 if (handler != null) { if (this.mappedHandlers != null && this.mappedHandlers.contains(handler)) { return true; } 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); } 

比较简单的实现类，可以配绑定viewName和exception以完成简单的异常映射视图页面

 protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) { // Expose ModelAndView for chosen error view. String viewName = determineViewName(ex, request); if (viewName != null) { //如果配置了statusCodes属性，则对此异常的状态码进行设置 Integer statusCode = determineStatusCode(request, viewName); if (statusCode != null) { applyStatusCodeIfPossible(request, response, statusCode); } //创建ModelAndView对象 return getModelAndView(viewName, ex, request); } else { return null; } } 

针对以上的源码我们分两步去简单分析下

 protected String determineViewName(Exception ex, HttpServletRequest request) { String viewName = null; //判断异常是否属于excludeExceptions集合内，是则直接返回null if (this.excludedExceptions != null) { for (Class<?> excludedEx : this.excludedExceptions) { if (excludedEx.equals(ex.getClass())) { return null; } } } // Check for specific exception mappings. // 从exceptionMappings集合内根据exception获取到相应的viewName if (this.exceptionMappings != null) { viewName = findMatchingViewName(this.exceptionMappings, ex); } //当exceptionMappings集合内不存在指定的exception但是默认视图指定则直接返回默认视图 if (viewName == null && this.defaultErrorView != null) { viewName = this.defaultErrorView; } return viewName; } 

• excludedExceptions集合可以过滤指定的exception，对其不进行解析直接返回null。可配置

• exceptionMappings绑定了exception与viewName的关系，如果在其集合内没找到相应的viewName，但是defaultErrorView属性指定，则会直接返回defaultErrorView对应的视图

 protected ModelAndView getModelAndView(String viewName, Exception ex) { ModelAndView mv = new ModelAndView(viewName); //exceptionAttribute默认为exception if (this.exceptionAttribute != null) { //将exception信息添加到model中 mv.addObject(this.exceptionAttribute, ex); } return mv; } 

主要就是将exceptionAttribute对应的参数值默认为exception属性添加到视图对象的model中

主要是解析带有@ResponseStatus的异常类，将其中的异常信息描述直接返回给客户端

 @Override protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) { //获取相应类上的注解@ResponseStatus ResponseStatus responseStatus = AnnotatedElementUtils.findMergedAnnotation(ex.getClass(), ResponseStatus.class); if (responseStatus != null) { try { return resolveResponseStatus(responseStatus, request, response, handler, ex); } catch (Exception resolveEx) { logger.warn("Handling of @ResponseStatus resulted in Exception", resolveEx); } } else if (ex.getCause() instanceof Exception) { ex = (Exception) ex.getCause(); //递归 return doResolveException(request, response, handler, ex); } return null; } 

读取@ResponseStatus注解信息，返回异常内容给客户端

 protected ModelAndView resolveResponseStatus(ResponseStatus responseStatus, HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception { //状态码 int statusCode = responseStatus.code().value(); //异常原因描述 String reason = responseStatus.reason(); if (this.messageSource != null) { reason = this.messageSource.getMessage(reason, null, reason, LocaleContextHolder.getLocale()); } //通过response对象直接返回错误信息给客户端 if (!StringUtils.hasLength(reason)) { response.sendError(statusCode); } else { //通过response对象直接返回错误信息给客户端 response.sendError(statusCode, reason); } return new ModelAndView(); } 

源码就不公布了，读者可自行去查询，基本都是调用response的sendError()方法返回错误信息给客户端。本文对其中的异常归下类

1. 请求方式异常

• HttpRequestMethodNotSupportedException-服务端不支持相应的请求方法
• HttpMediaTypeNotSupportedException/HttpMediaTypeNotAcceptableException-服务端/客户端不支持相应的mediaType，比如application/json
• MissingPathVariableException-@PathVaribale指定参数请求中不包含
• MissingServletRequestParameterException/ServletRequestBindingException-请求参数绑定错误
• MethodArgumentNotValidException-@Valid注解指定的参数校验失败
• AsyncRequestTimeoutException-异步请求超时

2. 消息内容异常

• ConversionNotSupportedException-服务端找寻不到相应的Convert对象来解析javabean
• TypeMismatchException-设置javabean属性类型出错
• HttpMessageNotReadableException/HttpMessageNotWritableException-消息内容不可读/不可写
• MissingServletRequestPartException-文件上传类错误，可能请求没有multipart/form-data或者服务不支持文件上传
• NoHandlerFoundException-handler处理器没有找到，即可能没有对应的请求处理供响应

具体的逻辑本文则不展开了，简述下其中的逻辑：
当处理handlerMethod业务逻辑过程中出现了异常，则此解析器

1. 尝试从handlerMethod所在的class类去找寻是否含有@ExceptionHandler注解的方法

2. 判断@ExceptionHandler指定的exception类与产生的异常一致，一致则执行相应的方法，当有多个@ExceptionHandler(value)，则默认采用第一个

3. 当上述在class类找寻不到则尝试判断class类是否含有@ControllerAdvice注解，有则按照上述第一二步的步骤再次找寻@ControllerAdvice指定的类

springmvc开放了对异常也可以包装成页面显示的功能，通过本文的简单分析可以帮助博主和读者更好的理解springmvc对异常的处理

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