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
实际应用
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
HandlerExceptionResolver-异常解析接口
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);
AbstractHandlerExceptionResolver-异常解析抽象基类
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);
}
1. SimpleMappingExceptionResolver-异常映射实现类
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
SimpleMappingExceptionResolver#determineViewName()-找寻viewName
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
SimpleMappingExceptionResolver#getModelAndView()-创建ModelAndView对象
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
2. ResponseStatusExceptionResolver-响应状态异常解析类
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;
}
ResponseStatusExceptionResolver#resolveResponseStatus()-返回异常信息给客户端
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();
}
3. DefaultHandlerExceptionResolver-springmvc默认的异常解析处理
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
- 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
- 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
4. ExceptionHandlerExceptionResolver-处理handlerMethod对象过程中的异常
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
尝试从handlerMethod所在的class类去找寻是否含有
@ExceptionHandler注解的方法判断
@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
小结
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