Spring MVC异常处理详解

Spring MVC中异常处理的类体系结构

下图中，我画出了Spring MVC中，跟异常处理相关的主要类和接口。

在Spring MVC中，所有用于处理在请求映射和请求处理过程中抛出的异常的类，都要实现HandlerExceptionResolver接口。AbstractHandlerExceptionResolver实现该接口和Orderd接口，是HandlerExceptionResolver类的实现的基类。ResponseStatusExceptionResolver等具体的异常处理类均在AbstractHandlerExceptionResolver之上，实现了具体的异常处理方式。一个基于Spring MVC的Web应用程序中，可以存在多个实现了HandlerExceptionResolver的异常处理类，他们的执行顺序，由其order属性决定, order值越小，越是优先执行, 在执行到第一个返回不是null的ModelAndView的Resolver时，不再执行后续的尚未执行的Resolver的异常处理方法。。

下面我逐个介绍一下SpringMVC提供的这些异常处理类的功能。

DefaultHandlerExceptionResolver

HandlerExceptionResolver接口的默认实现，基本上是Spring MVC内部使用，用来处理Spring定义的各种标准异常，将其转化为相对应的HTTP Status Code。其处理的异常类型有：

handleNoSuchRequestHandlingMethod handleHttpRequestMethodNotSupported handleHttpMediaTypeNotSupported handleMissingServletRequestParameter handleServletRequestBindingException handleTypeMismatch handleHttpMessageNotReadable handleHttpMessageNotWritable handleMethodArgumentNotValidException handleMissingServletRequestParameter handleMissingServletRequestPartException handleBindException

ResponseStatusExceptionResolver

用来支持ResponseStatus的使用，处理使用了ResponseStatus注解的异常，根据注解的内容，返回相应的HTTP Status Code和内容给客户端。如果Web应用程序中配置了ResponseStatusExceptionResolver，那么我们就可以使用ResponseStatus注解来注解我们自己编写的异常类，并在Controller中抛出该异常类，之后ResponseStatusExceptionResolver就会自动帮我们处理剩下的工作。

这是一个自己编写的异常，用来表示订单不存在：

 @ResponseStatus(value=HttpStatus.NOT_FOUND, reason="No such Order")  // 404     public class OrderNotFoundException extends RuntimeException {         // ...     }

这是一个使用该异常的Controller方法：

@RequestMapping(value="/orders/{id}", method=GET)     public String showOrder(@PathVariable("id") long id, Model model) {         Order order = orderRepository.findOrderById(id);         if (order == null) throw new OrderNotFoundException(id);         model.addAttribute(order);         return "orderDetail";     }

这样，当OrderNotFoundException被抛出时，ResponseStatusExceptionResolver会返回给客户端一个HTTP Status Code为404的响应。

AnnotationMethodHandlerExceptionResolver和ExceptionHandlerExceptionResolver

用来支持ExceptionHandler注解，使用被ExceptionHandler注解所标记的方法来处理异常。其中AnnotationMethodHandlerExceptionResolver在3.0版本中开始提供，ExceptionHandlerExceptionResolver在3.1版本中开始提供，从3.2版本开始，Spring推荐使用ExceptionHandlerExceptionResolver。如果配置了AnnotationMethodHandlerExceptionResolver和ExceptionHandlerExceptionResolver这两个异常处理bean之一，那么我们就可以使用ExceptionHandler注解来处理异常。

下面是几个ExceptionHandler注解的使用例子：

@Controller public class ExceptionHandlingController {    // @RequestHandler methods   ...      // 以下是异常处理方法      // 将DataIntegrityViolationException转化为Http Status Code为409的响应   @ResponseStatus(value=HttpStatus.CONFLICT, reason="Data integrity violation")  // 409   @ExceptionHandler(DataIntegrityViolationException.class)   public void conflict() {     // Nothing to do   }      // 针对SQLException和DataAccessException返回视图databaseError   @ExceptionHandler({SQLException.class,DataAccessException.class})   public String databaseError() {     // Nothing to do.  Returns the logical view name of an error page, passed to     // the view-resolver(s) in usual way.     // Note that the exception is _not_ available to this view (it is not added to     // the model) but see "Extending ExceptionHandlerExceptionResolver" below.     return "databaseError";   }    // 创建ModleAndView，将异常和请求的信息放入到Model中，指定视图名字，并返回该ModleAndView   @ExceptionHandler(Exception.class)   public ModelAndView handleError(HttpServletRequest req, Exception exception) {     logger.error("Request: " + req.getRequestURL() + " raised " + exception);      ModelAndView mav = new ModelAndView();     mav.addObject("exception", exception);     mav.addObject("url", req.getRequestURL());     mav.setViewName("error");     return mav;   } }

需要注意的是，上面例子中的ExceptionHandler方法的作用域，只是在本Controller类中。如果需要使用ExceptionHandler来处理全局的Exception，则需要使用ControllerAdvice注解。

@ControllerAdvice class GlobalDefaultExceptionHandler {     public static final String DEFAULT_ERROR_VIEW = "error";     @ExceptionHandler(value = Exception.class)     public ModelAndView defaultErrorHandler(HttpServletRequest req, Exception e) throws Exception {  // 如果异常使用了ResponseStatus注解，那么重新抛出该异常，Spring框架会处理该异常。   if (AnnotationUtils.findAnnotation(e.getClass(), ResponseStatus.class) != null)      throw e;  // 否则创建ModleAndView，处理该异常。  ModelAndView mav = new ModelAndView();  mav.addObject("exception", e);  mav.addObject("url", req.getRequestURL());  mav.setViewName(DEFAULT_ERROR_VIEW);  return mav;     } } 

SimpleMappingExceptionResolver

提供了将异常映射为视图的能力，高度可定制化。其提供的能力有：

1. 根据异常的类型，将异常映射到视图；
2. 可以为不符合处理条件没有被处理的异常，指定一个默认的错误返回；
3. 处理异常时，记录log信息；
4. 指定需要添加到Modle中的Exception属性，从而在视图中展示该属性。

@Configuration @EnableWebMvc  public class MvcConfiguration extends WebMvcConfigurerAdapter {     @Bean(name="simpleMappingExceptionResolver")     public SimpleMappingExceptionResolver createSimpleMappingExceptionResolver() {  SimpleMappingExceptionResolver r = new SimpleMappingExceptionResolver();  Properties mappings = new Properties();  mappings.setProperty("DatabaseException", "databaseError");  mappings.setProperty("InvalidCreditCardException", "creditCardError");  r.setExceptionMappings(mappings);  // 默认为空  r.setDefaultErrorView("error");    // 默认没有  r.setExceptionAttribute("ex");   r.setWarnLogCategory("example.MvcLogger");   return r;     }     ... } 

自定义ExceptionResolver

Spring MVC的异常处理非常的灵活，如果提供的ExceptionResolver类不能满足使用，我们可以实现自己的异常处理类。可以通过继承SimpleMappingExceptionResolver来定制Mapping的方式和能力，也可以直接继承AbstractHandlerExceptionResolver来实现其它类型的异常处理类。

Spring MVC是如何创建和使用这些Resolver的？

首先看Spring MVC是怎么加载异常处理bean的。

1. Spring MVC有两种加载异常处理类的方式，一种是根据类型，这种情况下，会加载ApplicationContext下所有实现了ExceptionResolver接口的bean，并根据其order属性排序，依次调用；一种是根据名字，这种情况下会加载ApplicationContext下，名字为handlerExceptionResolver的bean。
2. 不管使用那种加载方式，如果在ApplicationContext中没有找到异常处理bean，那么Spring MVC会加载默认的异常处理bean。
3. 默认的异常处理bean定义在DispatcherServlet.properties中。

org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,/  org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,/  org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

以下代码摘自ispatcherServlet，描述了异常处理类的加载过程：

/**  * Initialize the HandlerMappings used by this class.  * <p>If no HandlerMapping beans are defined in the BeanFactory for this namespace,  * we default to BeanNameUrlHandlerMapping.  */ private void initHandlerMappings(ApplicationContext context) {  this.handlerMappings = null;   if (this.detectAllHandlerMappings) {   // Find all HandlerMappings in the ApplicationContext, including ancestor contexts.   Map<String, HandlerMapping> matchingBeans =     BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);   if (!matchingBeans.isEmpty()) {    this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());    // We keep HandlerMappings in sorted order.    OrderComparator.sort(this.handlerMappings);   }  }  else {   try {    HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);    this.handlerMappings = Collections.singletonList(hm);   }   catch (NoSuchBeanDefinitionException ex) {    // Ignore, we'll add a default HandlerMapping later.   }  }   // Ensure we have at least one HandlerMapping, by registering  // a default HandlerMapping if no other mappings are found.  if (this.handlerMappings == null) {   this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);   if (logger.isDebugEnabled()) {    logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");   }  } }

然后看Spring MVC是怎么使用异常处理bean的。

1. Spring MVC把请求映射和处理过程放到try catch中，捕获到异常后，使用异常处理bean进行处理。
2. 所有异常处理bean按照order属性排序，在处理过程中，遇到第一个成功处理异常的异常处理bean之后，不再调用后续的异常处理bean。

以下代码摘自DispatcherServlet，描述了处理异常的过程。

/**  * Process the actual dispatching to the handler.  * <p>The handler will be obtained by applying the servlet's HandlerMappings in order.  * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters  * to find the first that supports the handler class.  * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers  * themselves to decide which methods are acceptable.  * @param request current HTTP request  * @param response current HTTP response  * @throws Exception in case of any kind of processing failure  */ 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 || mappedHandler.getHandler() == 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 (logger.isDebugEnabled()) {      logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);     }     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(request, mv);    mappedHandler.applyPostHandle(processedRequest, response, mv);   }   catch (Exception ex) {    dispatchException = ex;   }   processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);  }  catch (Exception ex) {   triggerAfterCompletion(processedRequest, response, mappedHandler, ex);  }  catch (Error err) {   triggerAfterCompletionWithError(processedRequest, response, mappedHandler, 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);    }   }  } }   /**  * Determine an error ModelAndView via the registered HandlerExceptionResolvers.  * @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 ModelAndView to forward to  * @throws Exception if no error ModelAndView found  */ protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,   Object handler, Exception ex) throws Exception {   // Check registered HandlerExceptionResolvers...  ModelAndView exMv = null;  for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {   exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);   if (exMv != null) {    break;   }  }  if (exMv != null) {   if (exMv.isEmpty()) {    request.setAttribute(EXCEPTION_ATTRIBUTE, ex);    return null;   }   // We might still need view name translation for a plain error model...   if (!exMv.hasView()) {    exMv.setViewName(getDefaultViewName(request));   }   if (logger.isDebugEnabled()) {    logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);   }   WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());   return exMv;  }   throw ex; }

何时该使用何种ExceptionResolver？

Spring提供了很多选择和非常灵活的使用方式，下面是一些使用建议：

1. 如果自定义异常类，考虑加上ResponseStatus注解；
2. 对于没有ResponseStatus注解的异常，可以通过使用ExceptionHandler+ControllerAdvice注解，或者通过配置SimpleMappingExceptionResolver，来为整个Web应用提供统一的异常处理。
3. 如果应用中有些异常处理方式，只针对特定的Controller使用，那么在这个Controller中使用ExceptionHandler注解。
4. 不要使用过多的异常处理方式，不然的话，维护起来会很苦恼，因为异常的处理分散在很多不同的地方。