@ SpringMVC 中针对异常问题有一套完整的处理体系,这套体系非常好用,今天松哥就花点时间来和大家聊一聊 SpringMVC 中的异常处理体系,我们把 SpringMVC 中的异常体系从头到尾梳理一下。 在 SpringMVC 的异常体系中,处于最顶层的大 Boss 是 HandlerExceptionResolver,这是一个接口,里边只有一个方法: resolveException 方法就用来解析请求处理过程中所产生的异常,并最终返回一个 ModelAndView。 我们来看下 HandlerExceptionResolver 的实现类: 直接实现 HandlerExceptionResolver 接口的类有三个: 在 SpringMVC 中,大致的异常解析器就是这些,接下来我们来逐个学习这些异常解析器。 AbstractHandlerExceptionResolver 是真正干活的异常解析器的父类,我们就先从他的 resolveException 方法开始看起。 记录异常日志没啥好说的,doResolveException 则是一个空的模版方法,所以这里对我们来说主要就是两个方法:shouldApplyTo 和 prepareResponse,我们分别来看。 shouldApplyTo 这里涉及到了两个对象:mappedHandlers 和 mappedHandlerClasses: 我们在配置异常解析器的时候可以配置这两个对象,进而实现该异常处理器只为某一个处理器服务,但是一般来说没这种需求,所以大家仅做了解即可。 如果开发者一开始配置了 mappedHandlers 或者 mappedHandlerClasses,则用这两个和处理器去比较,否则就直接返回 true,表示支持该异常处理。 prepareResponse prepareResponse 方法比较简单,主要是处理一下响应头的缓存字段。 这是 AbstractHandlerExceptionResolver 的大致内容,可以看到还是非常 easy 的,接下来我们来看它的实现类。 AbstractHandlerMethodExceptionResolver 主要是重写了 shouldApplyTo 方法和 doResolveException 方法,一个一个来看。 shouldApplyTo 这块感觉没啥好说的,判断逻辑基本上都还是调用父类的 shouldApplyTo 方法去处理。 doResolveException doResolveException 是具体的异常处理方法,但是它里边却没有实质性操作,具体的事情交给 doResolveHandlerMethodException 方法去做了,而该方法是一个抽象方法,具体的实现在子类中。 AbstractHandlerMethodExceptionResolver 只有一个子类就是 ExceptionHandlerExceptionResolver,来看下它的 doResolveHandlerMethodException 方法: 这个方法虽然比较长,但是很好理解: 这就是 ExceptionHandlerExceptionResolver 的大致工作流程,可以看到,还是非常 easy 的。 这个看名字就知道是一个默认的异常处理器,用来处理一些常见的异常类型,我们来看一下它的 doResolveException 方法: 可以看到,这里实际上就是根据不同的异常类型,然后调用不同的类去处理该异常。这里相关的处理都比较容易,以 HttpRequestMethodNotSupportedException 为例,异常处理就是对 response 对象做一些配置,如下: 配置响应头,然后 sendError,最后返回一个空的 ModelAndView 对象。 其实这里哥哥异常处理方法都大同小异,松哥就不再赘述啦。 这个用来处理 ResponseStatusException 类型的异常,或者使用了 @ResponseStatus 注解标记的普通异常类。我们来看下它的 doResolveException 方法: 可以看到,首先判断异常类型是不是 ResponseStatusException,如果是,则直接调用 resolveResponseStatusException 方法进行异常信息处理,如果不是,则去查找到异常类上的 @ResponseStatus 注解,并从中查找出相关的异常信息,然后调用 resolveResponseStatus 方法进行处理。 可以看到,ResponseStatusExceptionResolver 处理的异常类型有两种: 这个比较简单,没啥好说的。 SimpleMappingExceptionResolver 则是根据不同的异常显示不同的 error 页面。可能有的小伙伴还没用过 SimpleMappingExceptionResolver,所以松哥这里先简单说一下用法。 SimpleMappingExceptionResolver 的配置非常简单,直接提供一个 SimpleMappingExceptionResolver 的实例即可,如下: 在 mappings 中配置异常和 view 之间的对应关系,要写异常类的全路径,后面的 11、22 则表示视图名称;statusCodes 中配置了视图和响应状态码之间的映射关系。配置完成后,如果我们的项目在运行时抛出了 ArithmeticException 异常,则会展示出 11 视图,如果我们的项目在运行时抛出了 NullPointerException 异常,则会展示出 22 视图。 这是用法,了解了用法之后我们再来看源码,就容易理解了,我们直接来看 doResolveException 方法: 在上面这个过程中,有两个比较长的方法,松哥这里需要和大家额外多说两句。 determineViewName 这个就是根据异常类型找到视图名,我们来看下具体的查找方式: determineStatusCode 这个就比较容易,直接去 statusCodes 中查看是否有视图对应的状态码,如果有则直接返回,如果没有,就返回一个默认的。 最后,还有一个 HandlerExceptionResolverComposite 需要和大家介绍下,这是一个组合的异常处理器,用来代理哪些真正干活的异常处理器。 它的 resolveException 方法就比较简单了,这种写法我们已经见到过很多次了,不再赘述。 好啦,今天就和大家简单聊一聊 SpringMVC 中的异常处理体系,整体来说并不难,小伙伴们可以仔细品一品。1.异常解析器概览
public interface HandlerExceptionResolver {
@Nullable
ModelAndView resolveException(
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex);
}
2.AbstractHandlerExceptionResolver
@Override
@Nullable
public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {
if (shouldApplyTo(request, handler)) {
prepareResponse(ex, response);
ModelAndView result = doResolveException(request, response, handler, ex);
if (result != null) {
logException(ex, request);
}
return result;
}
else {
return null;
}
}
protected boolean shouldApplyTo(HttpServletRequest request, @Nullable Object handler) {
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;
}
}
}
}
return !hasHandlerMappings();
}
protected void prepareResponse(Exception ex, HttpServletResponse response) {
if (this.preventResponseCaching) {
preventCaching(response);
}
}
protected void preventCaching(HttpServletResponse response) {
response.addHeader(HEADER_CACHE_CONTROL, "no-store");
}
2.1 AbstractHandlerMethodExceptionResolver
@Override
protected boolean shouldApplyTo(HttpServletRequest request, @Nullable Object handler) {
if (handler == null) {
return super.shouldApplyTo(request, null);
}
else if (handler instanceof HandlerMethod) {
HandlerMethod handlerMethod = (HandlerMethod) handler;
handler = handlerMethod.getBean();
return super.shouldApplyTo(request, handler);
}
else if (hasGlobalExceptionHandlers() && hasHandlerMappings()) {
return super.shouldApplyTo(request, handler);
}
else {
return false;
}
}
@Override
@Nullable
protected final ModelAndView doResolveException(
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {
HandlerMethod handlerMethod = (handler instanceof HandlerMethod ? (HandlerMethod) handler : null);
return doResolveHandlerMethodException(request, response, handlerMethod, ex);
}
@Nullable
protected abstract ModelAndView doResolveHandlerMethodException(
HttpServletRequest request, HttpServletResponse response, @Nullable HandlerMethod handlerMethod, Exception ex);
2.1.1 ExceptionHandlerExceptionResolver
@Override
@Nullable
protected ModelAndView doResolveHandlerMethodException(HttpServletRequest request,
HttpServletResponse response, @Nullable HandlerMethod handlerMethod, Exception exception) {
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();
ArrayList<Throwable> exceptions = new ArrayList<>();
try {
if (logger.isDebugEnabled()) {
logger.debug("Using @ExceptionHandler " + exceptionHandlerMethod);
}
// Expose causes as provided arguments as well
Throwable exToExpose = exception;
while (exToExpose != null) {
exceptions.add(exToExpose);
Throwable cause = exToExpose.getCause();
exToExpose = (cause != exToExpose ? cause : null);
}
Object[] arguments = new Object[exceptions.size() + 1];
exceptions.toArray(arguments); // efficient arraycopy call in ArrayList
arguments[arguments.length - 1] = handlerMethod;
exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, arguments);
}
catch (Throwable invocationEx) {
// Any other than the original exception (or a cause) is unintended here,
// probably an accident (e.g. failed assertion or the like).
if (!exceptions.contains(invocationEx) && 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;
}
}
2.2 DefaultHandlerExceptionResolver
@Override
@Nullable
protected ModelAndView doResolveException(
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {
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) {
}
return null;
}
protected ModelAndView handleHttpRequestMethodNotSupported(HttpRequestMethodNotSupportedException ex,
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler) throws IOException {
String[] supportedMethods = ex.getSupportedMethods();
if (supportedMethods != null) {
response.setHeader("Allow", StringUtils.arrayToDelimitedString(supportedMethods, ", "));
}
response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, ex.getMessage());
return new ModelAndView();
}
2.3 ResponseStatusExceptionResolver
@Override
@Nullable
protected ModelAndView doResolveException(
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {
try {
if (ex instanceof ResponseStatusException) {
return resolveResponseStatusException((ResponseStatusException) ex, request, response, handler);
}
ResponseStatus status = AnnotatedElementUtils.findMergedAnnotation(ex.getClass(), ResponseStatus.class);
if (status != null) {
return resolveResponseStatus(status, request, response, handler, ex);
}
if (ex.getCause() instanceof Exception) {
return doResolveException(request, response, handler, (Exception) ex.getCause());
}
}
catch (Exception resolveEx) {
}
return null;
}
2.4 SimpleMappingExceptionResolver
@Bean
SimpleMappingExceptionResolver simpleMappingExceptionResolver() {
SimpleMappingExceptionResolver resolver = new SimpleMappingExceptionResolver();
Properties mappings = new Properties();
mappings.put("java.lang.ArithmeticException", "11");
mappings.put("java.lang.NullPointerException", "22");
resolver.setExceptionMappings(mappings);
Properties statusCodes = new Properties();
statusCodes.put("11", "500");
statusCodes.put("22", "500");
resolver.setStatusCodes(statusCodes);
return resolver;
}
@Override
@Nullable
protected ModelAndView doResolveException(
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {
String viewName = determineViewName(ex, request);
if (viewName != null) {
Integer statusCode = determineStatusCode(request, viewName);
if (statusCode != null) {
applyStatusCodeIfPossible(request, response, statusCode);
}
return getModelAndView(viewName, ex, request);
}
else {
return null;
}
}
@Nullable
protected String determineViewName(Exception ex, HttpServletRequest request) {
String viewName = null;
if (this.excludedExceptions != null) {
for (Class<?> excludedEx : this.excludedExceptions) {
if (excludedEx.equals(ex.getClass())) {
return null;
}
}
}
if (this.exceptionMappings != null) {
viewName = findMatchingViewName(this.exceptionMappings, ex);
}
if (viewName == null && this.defaultErrorView != null) {
viewName = this.defaultErrorView;
}
return viewName;
}
@Nullable
protected Integer determineStatusCode(HttpServletRequest request, String viewName) {
if (this.statusCodes.containsKey(viewName)) {
return this.statusCodes.get(viewName);
}
return this.defaultStatusCode;
}
3.HandlerExceptionResolverComposite
@Override
@Nullable
public ModelAndView resolveException(
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {
if (this.resolvers != null) {
for (HandlerExceptionResolver handlerExceptionResolver : this.resolvers) {
ModelAndView mav = handlerExceptionResolver.resolveException(request, response, handler, ex);
if (mav != null) {
return mav;
}
}
}
return null;
}
4.小结