在Spring MVC中，如果对异常不做任何处理，Spring MVC会将异常直接抛给容器。

例如下面的代码抛出了异常：

@GetMapping("e1")
public String exception() {int i = 1 / 0;return "exception";
}

浏览器页面上会显示500错误。

对异常的处理

@ExceptionHandler处理当前Controller的异常

@ExceptionHandler能对当前Controller中指定的异常进行处理，可以通过ModelAndView将异常信息传递给页面。

使用如下：

@GetMapping("e1")
public String exception() {int i = 1 / 0;return "exception";
}@ExceptionHandler(value = RuntimeException.class)
public ModelAndView handlerRuntimeException(Exception exception) {ModelAndView mv = new ModelAndView("error");mv.addObject("exception", exception);return mv;
}

@ExceptionHandler要注意异常的优先级，如果Controller中有如下的异常处理方法，那么还是会执行handlerArithmeticException()方法，因为ArithmeticException异常更加具体：

@ExceptionHandler(value = RuntimeException.class)
public ModelAndView handlerRuntimeException(Exception exception) {ModelAndView mv = new ModelAndView("error");mv.addObject("exception", exception);return mv;
}

@ControllerAdvice处理全局异常

@ExceptionHandler的作用域是当前Controller，如果想对全局的异常进行处理需要使用@ControllerAdvice。

使用如下：

@ControllerAdvice
public class ExceptionHandlerControllerAdvice {@ExceptionHandler(value = ArithmeticException.class)public ModelAndView handlerArithmeticException(Exception exception) {ModelAndView mv = new ModelAndView("error");mv.addObject("exception", exception);return mv;}}

如果Controller中使用了@ExceptionHandler处理异常，那么他的优先级比全局的异常处理高。

@ResponseStatus定制错误码和错误内容

可以使用@ResponseStatus加到异常类上，这样当这个异常抛出时，页面显示的是定制的错误消息。

异常类定义如下：

@ResponseStatus(value = HttpStatus.FORBIDDEN, reason = "用户名和密码不匹配")
public class UsernameNotMatchPasswordException extends RuntimeException {}

在方法中抛出这个异常：

/*** 使用@ResponseStatus定义错误码和错误内容* @param i* @return*/
@GetMapping("e3")
public String exception3(int i) {if (13 == i) {throw new UsernameNotMatchPasswordException();}return "success";
}

页面显示的错误消息如下：

使用SimpleMappingExceptionResolver处理指定异常

注入SimpleMappingExceptionResolver，并指定要处理的异常与视图。

com.morris.spring.mvc.config.MVCConfig#extendHandlerExceptionResolvers

public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {SimpleMappingExceptionResolver simpleMappingExceptionResolver = new SimpleMappingExceptionResolver();Properties properties = new Properties();// 指定要处理的异常与视图properties.setProperty("java.lang.NullPointerException", "error");simpleMappingExceptionResolver.setExceptionMappings(properties);resolvers.add(simpleMappingExceptionResolver);}

在Controller中抛出指定的异常：

/*** 使用SimpleMappingExceptionResolver处理异常** @return*/
@GetMapping("e5")
public String exception5() {if(true) {throw new NullPointerException();}return "success";
}

这样就会跳到指定的视图error.jsp页面。

自定义HandlerExceptionResolver

如果觉得SpringMVC提供的异常处理不满足需求，可以实现HandlerExceptionResolver接口自定义异常处理。

package com.morris.spring.mvc.exception;import org.springframework.core.PriorityOrdered;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;@Component
public class MyHandlerExceptionResolver extends AbstractHandlerExceptionResolver implements PriorityOrdered {@Overrideprotected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {if(ex instanceof ArrayIndexOutOfBoundsException) {ModelAndView mv = new ModelAndView("error");mv.addObject("exception", "MyHandlerExceptionResolver");return mv;}return null;}/*** 优先级设置高一点，否则会被@ControllerAdvice全局异常处理* @return*/@Overridepublic int getOrder() {return 1;}
}

总结：不管使用上面哪种异常处理方法，只能处理在请求到达了DispatcherServlet，并且出现了异常后进入processDispatchResult()方法。

下面的这两种异常场景不适用：

请求没有到达DispatcherServlet的核心流程，如在filter中抛出异常。
请求进入processDispatchResult()方法处理异常，但是在处理过程中有抛出了异常，如在@ControllerAdvice方法中抛出了异常。

源码分析

HandlerExceptionResolverComposite的调用过程

在处理controller的返回结果时，发现有异常就会调用异常处理的逻辑：

org.springframework.web.servlet.DispatcherServlet#processDispatchResult

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,@Nullable Exception exception) throws Exception {boolean errorView = false;if (exception != null) {if (exception instanceof ModelAndViewDefiningException) {logger.debug("ModelAndViewDefiningException encountered", exception);mv = ((ModelAndViewDefiningException) exception).getModelAndView();}else {Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);// 异常处理mv = processHandlerException(request, response, handler, exception);errorView = (mv != null);}}
... ...

org.springframework.web.servlet.DispatcherServlet#processHandlerException

protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,@Nullable Object handler, Exception ex) throws Exception {// Success and error responses may use different content typesrequest.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);// Check registered HandlerExceptionResolvers...ModelAndView exMv = null;if (this.handlerExceptionResolvers != null) {/*** handlerExceptionResolvers什么时候初始化的？* @see DispatcherServlet#initHandlerExceptionResolvers(org.springframework.context.ApplicationContext)** @see AbstractHandlerExceptionResolver#resolveException(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, java.lang.Object, java.lang.Exception)* @see HandlerExceptionResolverComposite#resolveException(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, java.lang.Object, java.lang.Exception)*/for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {exMv = resolver.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()) {String defaultViewName = getDefaultViewName(request);if (defaultViewName != null) {exMv.setViewName(defaultViewName);}}if (logger.isTraceEnabled()) {logger.trace("Using resolved error view: " + exMv, ex);}else if (logger.isDebugEnabled()) {logger.debug("Using resolved error view: " + exMv);}WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());return exMv;}throw ex;
}

handlerExceptionResolvers何时被初始化的？

org.springframework.web.servlet.DispatcherServlet#initHandlerExceptionResolvers

private void initHandlerExceptionResolvers(ApplicationContext context) {this.handlerExceptionResolvers = null;if (this.detectAllHandlerExceptionResolvers) {/*** HandlerExceptionResolver在WebMvcConfigurationSupport中注入了*/// Find all HandlerExceptionResolvers in the ApplicationContext, including ancestor contexts.Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);if (!matchingBeans.isEmpty()) {this.handlerExceptionResolvers = new ArrayList<>(matchingBeans.values());// We keep HandlerExceptionResolvers in sorted order.AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);}}else {try {HandlerExceptionResolver her =context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);this.handlerExceptionResolvers = Collections.singletonList(her);}catch (NoSuchBeanDefinitionException ex) {// Ignore, no HandlerExceptionResolver is fine too.}}// Ensure we have at least some HandlerExceptionResolvers, by registering// default HandlerExceptionResolvers if no other resolvers are found.if (this.handlerExceptionResolvers == null) {// 默认ExceptionHandlerExceptionResolver、ResponseStatusExceptionResolver、DefaultHandlerExceptionResolverthis.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);if (logger.isTraceEnabled()) {logger.trace("No HandlerExceptionResolvers declared in servlet '" + getServletName() +"': using default strategies from DispatcherServlet.properties");}}
}

handlerExceptionResolvers是从在SpringMVC容器中获取所有的HandlerExceptionResolver实例，那么这些实例是什么时候注入的呢？

org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport#handlerExceptionResolver

@Bean
public HandlerExceptionResolver handlerExceptionResolver(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager) {List<HandlerExceptionResolver> exceptionResolvers = new ArrayList<>();configureHandlerExceptionResolvers(exceptionResolvers);if (exceptionResolvers.isEmpty()) {// 添加默认的HandlerExceptionResolveraddDefaultHandlerExceptionResolvers(exceptionResolvers, contentNegotiationManager);}extendHandlerExceptionResolvers(exceptionResolvers);HandlerExceptionResolverComposite composite = new HandlerExceptionResolverComposite();composite.setOrder(0);composite.setExceptionResolvers(exceptionResolvers);return composite;
}protected final void addDefaultHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers,ContentNegotiationManager mvcContentNegotiationManager) {// 添加ExceptionHandlerExceptionResolverExceptionHandlerExceptionResolver exceptionHandlerResolver = createExceptionHandlerExceptionResolver();exceptionHandlerResolver.setContentNegotiationManager(mvcContentNegotiationManager);exceptionHandlerResolver.setMessageConverters(getMessageConverters());exceptionHandlerResolver.setCustomArgumentResolvers(getArgumentResolvers());exceptionHandlerResolver.setCustomReturnValueHandlers(getReturnValueHandlers());if (jackson2Present) {exceptionHandlerResolver.setResponseBodyAdvice(Collections.singletonList(new JsonViewResponseBodyAdvice()));}if (this.applicationContext != null) {exceptionHandlerResolver.setApplicationContext(this.applicationContext);}exceptionHandlerResolver.afterPropertiesSet();exceptionResolvers.add(exceptionHandlerResolver);// 添加ResponseStatusExceptionResolverResponseStatusExceptionResolver responseStatusResolver = new ResponseStatusExceptionResolver();responseStatusResolver.setMessageSource(this.applicationContext);exceptionResolvers.add(responseStatusResolver);// 添加DefaultHandlerExceptionResolverexceptionResolvers.add(new DefaultHandlerExceptionResolver());
}

默认注册了三个HandlerExceptionResolver：

ExceptionHandlerExceptionResolver
ResponseStatusExceptionResolver
DefaultHandlerExceptionResolver

我们可以通过实现WebMvcConfigurer接口extendHandlerExceptionResolvers()方法注入自己的HandlerExceptionResolver，也可以通过向SpringMVC容器中注入HandlerExceptionResolver实例。

最后ExceptionHandlerExceptionResolver、ResponseStatusExceptionResolver、DefaultHandlerExceptionResolver以及通过实现WebMvcConfigurer接口的extendHandlerExceptionResolvers()方法注入的HandlerExceptionResolver都会包装到HandlerExceptionResolverComposite中。

最后异常处理都会调用HandlerExceptionResolverComposite#resolveException

org.springframework.web.servlet.handler.HandlerExceptionResolverComposite#resolveException

public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {if (this.resolvers != null) {for (HandlerExceptionResolver handlerExceptionResolver : this.resolvers) {/*** @see AbstractHandlerExceptionResolver#resolveException(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, java.lang.Object, java.lang.Exception)*/ModelAndView mav = handlerExceptionResolver.resolveException(request, response, handler, ex);if (mav != null) {return mav;}}}return null;
}

然后会调用各个HandlerExceptionResolver的doResolveException()进行异常处理。

org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver#resolveException

public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {if (shouldApplyTo(request, handler)) {prepareResponse(ex, response);/*** @see DefaultHandlerExceptionResolver#doResolveException(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, java.lang.Object, java.lang.Exception)* @see ResponseStatusExceptionResolver#doResolveException(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, java.lang.Object, java.lang.Exception)* @see SimpleMappingExceptionResolver#doResolveException(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, java.lang.Object, java.lang.Exception)* @see AbstractHandlerMethodExceptionResolver#doResolveException(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, java.lang.Object, java.lang.Exception)**/// 让所有的ExceptionResolver按顺序挨个处理，有视图返回就救赎ModelAndView result = doResolveException(request, response, handler, ex);if (result != null) {// Print debug message when warn logger is not enabled.if (logger.isDebugEnabled() && (this.warnLogger == null || !this.warnLogger.isWarnEnabled())) {logger.debug("Resolved [" + ex + "]" + (result.isEmpty() ? "" : " to " + result));}// Explicitly configured warn logger in logException method.logException(ex, request);}return result;}else {return null;}
}

ExceptionHandlerExceptionResolver

ExceptionHandlerExceptionResolver从名字就可以看出是处理@ExceptionHandler注解的。

首先看下ExceptionHandlerExceptionResolver的afterPropertiesSet方法，主要解析@ControllerAdvice注解的类中的带有@ExceptionHandler的方法，建议异常与方法之间的映射关系，注意这里只解析了@ControllerAdvice注解的类中的带有@ExceptionHandler注解的方法，并没有解析Controller中带有ExceptionHandler注解的方法。

org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver#afterPropertiesSet

public void afterPropertiesSet() {// Do this first, it may add ResponseBodyAdvice beans// 解析带有@ControllerAdvice注解的类initExceptionHandlerAdviceCache();if (this.argumentResolvers == null) {List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);}if (this.returnValueHandlers == null) {List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);}
}private void initExceptionHandlerAdviceCache() {if (getApplicationContext() == null) {return;}// 从容器中查找所有带有ControllerAdvice注解的类List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());for (ControllerAdviceBean adviceBean : adviceBeans) {Class<?> beanType = adviceBean.getBeanType();if (beanType == null) {throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);}// 解析类中带有@ExceptionHandler的方法ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType);if (resolver.hasExceptionMappings()) {this.exceptionHandlerAdviceCache.put(adviceBean, resolver);}if (ResponseBodyAdvice.class.isAssignableFrom(beanType)) {this.responseBodyAdvice.add(adviceBean);}}if (logger.isDebugEnabled()) {int handlerSize = this.exceptionHandlerAdviceCache.size();int adviceSize = this.responseBodyAdvice.size();if (handlerSize == 0 && adviceSize == 0) {logger.debug("ControllerAdvice beans: none");}else {logger.debug("ControllerAdvice beans: " +handlerSize + " @ExceptionHandler, " + adviceSize + " ResponseBodyAdvice");}}
}

ExceptionHandlerExceptionResolver对异常的处理就是找到@ExceptionHandler注解的方法，并进行反射调用。

protected ModelAndView doResolveHandlerMethodException(HttpServletRequest request,HttpServletResponse response, @Nullable HandlerMethod handlerMethod, Exception exception) {// 不管是Controller中的@ExceptionHandler，还是ControllerAdvice中的@ExceptionHandler// 最终异常的处理都是要找到带有@ExceptionHandler注解的方法进行调用ServletInvocableHandlerMethod exceptionHandlerMethod = getExceptionHandlerMethod(handlerMethod, exception);if (exceptionHandlerMethod == null) {return null;}if (this.argumentResolvers != null) {exceptionHandlerMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);}if (this.returnValueHandlers != null) {exceptionHandlerMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);}ServletWebRequest webRequest = new ServletWebRequest(request, response);ModelAndViewContainer mavContainer = new ModelAndViewContainer();try {if (logger.isDebugEnabled()) {logger.debug("Using @ExceptionHandler " + exceptionHandlerMethod);}Throwable cause = exception.getCause();if (cause != null) {// Expose cause as provided argument as wellexceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, cause, handlerMethod);}else {// Otherwise, just the given exception as-isexceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, handlerMethod);}}catch (Throwable invocationEx) {// Any other than the original exception (or its cause) is unintended here,// probably an accident (e.g. failed assertion or the like).if (invocationEx != exception && invocationEx != exception.getCause() && logger.isWarnEnabled()) {logger.warn("Failure in @ExceptionHandler " + exceptionHandlerMethod, 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;}
}@Nullable
protected ServletInvocableHandlerMethod getExceptionHandlerMethod(@Nullable HandlerMethod handlerMethod, Exception exception) {Class<?> handlerType = null;if (handlerMethod != null) {// Local exception handler methods on the controller class itself.// To be invoked through the proxy, even in case of an interface-based proxy.handlerType = handlerMethod.getBeanType();ExceptionHandlerMethodResolver resolver = this.exceptionHandlerCache.get(handlerType);if (resolver == null) {// 解析controller中带有@ExceptionHandler注解的方法resolver = new ExceptionHandlerMethodResolver(handlerType);this.exceptionHandlerCache.put(handlerType, resolver);}// 根据异常找到@ExceptionHandler注解的方法Method method = resolver.resolveMethod(exception);if (method != null) {return new ServletInvocableHandlerMethod(handlerMethod.getBean(), method);}// For advice applicability check below (involving base packages, assignable types// and annotation presence), use target class instead of interface-based proxy.if (Proxy.isProxyClass(handlerType)) {handlerType = AopUtils.getTargetClass(handlerMethod.getBean());}}// 这里@ControllerAdvice全局异常的处理// exceptionHandlerAdviceCache属性在afterProperties()方法中初始化for (Map.Entry<ControllerAdviceBean, ExceptionHandlerMethodResolver> entry : this.exceptionHandlerAdviceCache.entrySet()) {ControllerAdviceBean advice = entry.getKey();if (advice.isApplicableToBeanType(handlerType)) {ExceptionHandlerMethodResolver resolver = entry.getValue();// 根据异常找到@ExceptionHandler注解的方法Method method = resolver.resolveMethod(exception);if (method != null) {return new ServletInvocableHandlerMethod(advice.resolveBean(), method);}}}return null;
}

ResponseStatusExceptionResolver

ResponseStatusExceptionResolver主要是要拿到异常类上面的@ResponseStatus注解，然后将response的状态和内容设置为@ResponseStatus注解中的内容。

org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver#doResolveException

protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {try {if (ex instanceof ResponseStatusException) {return resolveResponseStatusException((ResponseStatusException) ex, request, response, handler);}// 拿到异常上面的@ResponseStatus注解ResponseStatus status = AnnotatedElementUtils.findMergedAnnotation(ex.getClass(), ResponseStatus.class);if (status != null) {// 设置错误码和错误内容return resolveResponseStatus(status, request, response, handler, ex);}if (ex.getCause() instanceof Exception) {return doResolveException(request, response, handler, (Exception) ex.getCause());}}catch (Exception resolveEx) {if (logger.isWarnEnabled()) {logger.warn("Failure while trying to resolve exception [" + ex.getClass().getName() + "]", resolveEx);}}return null;
}

DefaultHandlerExceptionResolver

DefaultHandlerExceptionResolver是用来处理spring mvc内部异常，如HttpRequestMethodNotSupportedException、HttpMediaTypeNotSupportedException等异常。

protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {// 处理spring内部异常try {if (ex instanceof HttpRequestMethodNotSupportedException) {return handleHttpRequestMethodNotSupported((HttpRequestMethodNotSupportedException) ex, request, response, handler);}else if (ex instanceof HttpMediaTypeNotSupportedException) {return handleHttpMediaTypeNotSupported((HttpMediaTypeNotSupportedException) ex, request, response, handler);}else if (ex instanceof HttpMediaTypeNotAcceptableException) {return handleHttpMediaTypeNotAcceptable((HttpMediaTypeNotAcceptableException) ex, request, response, handler);}else if (ex instanceof MissingPathVariableException) {return handleMissingPathVariable((MissingPathVariableException) ex, request, response, handler);}else if (ex instanceof MissingServletRequestParameterException) {return handleMissingServletRequestParameter((MissingServletRequestParameterException) ex, request, response, handler);}else if (ex instanceof ServletRequestBindingException) {return handleServletRequestBindingException((ServletRequestBindingException) ex, request, response, handler);}else if (ex instanceof ConversionNotSupportedException) {return handleConversionNotSupported((ConversionNotSupportedException) ex, request, response, handler);}else if (ex instanceof TypeMismatchException) {return handleTypeMismatch((TypeMismatchException) ex, request, response, handler);}else if (ex instanceof HttpMessageNotReadableException) {return handleHttpMessageNotReadable((HttpMessageNotReadableException) ex, request, response, handler);}else if (ex instanceof HttpMessageNotWritableException) {return handleHttpMessageNotWritable((HttpMessageNotWritableException) ex, request, response, handler);}else if (ex instanceof MethodArgumentNotValidException) {return handleMethodArgumentNotValidException((MethodArgumentNotValidException) ex, request, response, handler);}else if (ex instanceof MissingServletRequestPartException) {return handleMissingServletRequestPartException((MissingServletRequestPartException) ex, request, response, handler);}else if (ex instanceof BindException) {return handleBindException((BindException) ex, request, response, handler);}else if (ex instanceof NoHandlerFoundException) {return handleNoHandlerFoundException((NoHandlerFoundException) ex, request, response, handler);}else if (ex instanceof AsyncRequestTimeoutException) {return handleAsyncRequestTimeoutException((AsyncRequestTimeoutException) ex, request, response, handler);}}catch (Exception handlerEx) {if (logger.isWarnEnabled()) {logger.warn("Failure while trying to resolve exception [" + ex.getClass().getName() + "]", handlerEx);}}return null;
}

SimpleMappingExceptionResolver

我们在构造SimpleMappingExceptionResolver时就会指定异常与视图的映射关系，在处理异常时只需要在映射map中获取即可。

protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {// Expose ModelAndView for chosen error view.// 将异常与属性exceptionMappings、excludedExceptions进行匹配，拿到视图名称String viewName = determineViewName(ex, request);if (viewName != null) {// Apply HTTP status code for error views, if specified.// Only apply it if we're processing a top-level request.Integer statusCode = determineStatusCode(request, viewName);if (statusCode != null) {applyStatusCodeIfPossible(request, response, statusCode);}return getModelAndView(viewName, ex, request);}else {return null;}
}protected String determineViewName(Exception ex, HttpServletRequest request) {String viewName = null;if (this.excludedExceptions != null) {// 与传入的异常的类型进行匹配for (Class<?> excludedEx : this.excludedExceptions) {if (excludedEx.equals(ex.getClass())) {return null;}}}// Check for specific exception mappings.if (this.exceptionMappings != null) {// 与传入的异常的名字进行匹配viewName = findMatchingViewName(this.exceptionMappings, ex);}// Return default error view else, if defined.if (viewName == null && this.defaultErrorView != null) {if (logger.isDebugEnabled()) {logger.debug("Resolving to default view '" + this.defaultErrorView + "'");}viewName = this.defaultErrorView;}return viewName;
}

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