开头
试想一下我们一般怎么统一处理异常呢,答:切面。但抛开切面不讲,如果对每一个controller方法抛出的异常做专门处理,那么着实太费劲了,有没有更好的方法呢?当然有,就是本篇文章接下来要介绍的springmvc的异常处理机制,用到了ControllerAdvice和ExceptionHandler注解,有点切面的感觉哈哈。
1.ExceptionHandlerExceptionResolver
首先从springmvc的异常处理解析器开始讲,当执行完controller方法后,不管有没有异常产生都会调用DispatcherServlet#doDispatch()
方法中的processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
方法,接着会判断是否有异常,若无异常则走正常流程,若有异常则需要进行处理 mv = processHandlerException(request, response, handler, exception);
再接着就是遍历spring已经注册的异常处理解析器直到有处理器返回mav
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
@Nullable Exception exception) throws Exception {
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
// 执行处理器产生的异常处理
mv = processHandlerException(request, response, handler, exception);
// 是否有异常视图返回
errorView = (mv != null);
}
}
// Did the handler return a view to render? 处理程序是否返回要渲染的视图
if (mv != null && !mv.wasCleared()) {
// 渲染视图
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
"': assuming HandlerAdapter completed request handling");
}
}
}
@Nullable
protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
@Nullable Object handler, Exception ex) throws Exception {
// Check registered HandlerExceptionResolvers...
ModelAndView exMv = null;
if (this.handlerExceptionResolvers != null) {
for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
if (exMv != null) {
break;
}
}
}
if (exMv != null) {
// 无视图view
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);
}
}
WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
return exMv;
}
throw ex;
}
其中最重要也是最常使用的一个处理器就是ExceptionHandlerExceptionResolver,下面将着重介绍它,先来看看这个类的继承结构图,实现了InitializingBean接口,在这个bean创建完成之前会调用生命周期初始化方法afterPropertiesSet()
,这里面包含了对@ControllerAdvice
注解的解析,初始化完后的信息供后续解析异常使用。
实现HandlerExceptionResolver
接口,实现解析方法resolveException()
public interface HandlerExceptionResolver {
@Nullable
ModelAndView resolveException(
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex);
}
@Override
public void afterPropertiesSet() {
// Do this first, it may add ResponseBodyAdvice beans
// 初始化异常注解 @ControllerAdvice
initExceptionHandlerAdviceCache();
}
private void initExceptionHandlerAdviceCache() {
if (getApplicationContext() == null) {
return;
}
if (logger.isDebugEnabled()) {
logger.debug("Looking for exception mappings: " + getApplicationContext());
}
// 解析有@ControllerAdvice注解的bean,并将这个bean构建成ControllerAdviceBean对象
List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
// 将ControllerAdviceBean根据order排序
AnnotationAwareOrderComparator.sort(adviceBeans);
for (ControllerAdviceBean adviceBean : adviceBeans) {
Class<?> beanType = adviceBean.getBeanType();
if (beanType == null) {
throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
}
ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType);
// mappedMethods 映射不为空
if (resolver.hasExceptionMappings()) {
// 添加到缓存中
this.exceptionHandlerAdviceCache.put(adviceBean, resolver);
if (logger.isInfoEnabled()) {
logger.info("Detected @ExceptionHandler methods in " + adviceBean);
}
}
// 若实现了ResponseBodyAdvice接口(暂不介绍)
if (ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
this.responseBodyAdvice.add(adviceBean);
if (logger.isInfoEnabled()) {
logger.info("Detected ResponseBodyAdvice implementation in " + adviceBean);
}
}
}
}
ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType);
这行代码会解析拥有@ControllerAdvice
注解的class,并且会遍历class中带有 @ExceptionHandler
注解的方法,获取方法注解带有的异常类型,将异常类型和方法放入到mappedMethods
中供后面获取,获取的时候若对应处理此异常类型的method有多个,则需要进行排序,选取一个异常类型与method ExceptionHandler注解异常类型最近的一个(深度最小的那个也即是继承关系最少的那个)具体代码如下:
ExceptionHandlerMethodResolver
@Override
@Nullable
protected ModelAndView doResolveHandlerMethodException(HttpServletRequest request,
HttpServletResponse response, @Nullable HandlerMethod handlerMethod, Exception exception) {
// exception为controller方法抛出的异常
// 根据异常及其类型从上述的mappedMethods中获取对应的方法,再获取方法所在的对象 封装成ServletInvocableHandlerMethod
ServletInvocableHandlerMethod exceptionHandlerMethod = getExceptionHandlerMethod(handlerMethod, exception);
if (exceptionHandlerMethod == null) {
return null;
}
// 设置参数解析器,主要用来获取方法的参数值的,供后续反射调用方法
if (this.argumentResolvers != null) {
exceptionHandlerMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
// 设置返回值解析器,当执行完方法后获取返回值,对返回值进行处理 或返回视图或将结果写入到response
if (this.returnValueHandlers != null) {
exceptionHandlerMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
ServletWebRequest webRequest = new ServletWebRequest(request, response);
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
try {
if (logger.isDebugEnabled()) {
logger.debug("Invoking @ExceptionHandler method: " + exceptionHandlerMethod);
}
Throwable cause = exception.getCause();
if (cause != null) {
// Expose cause as provided argument as well
// 执行异常处理方法,也就是我们的自定义的异常处理方法
exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, cause, handlerMethod);
}
else {
// Otherwise, just the given exception as-is
exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, handlerMethod);
}
}
catch (Throwable invocationEx) {
// Any other than the original exception is unintended here,
// probably an accident (e.g. failed assertion or the like).
if (invocationEx != exception && logger.isWarnEnabled()) {
logger.warn("Failed to invoke @ExceptionHandler method: " + exceptionHandlerMethod, invocationEx);
}
// Continue with default processing of the original exception...
return null;
}
// 根据后续的返回值解析器设置的,将返回值写入到response中了直接返回空的mav
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());
// (this.view instanceof String)
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;
}
}
exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, cause, handlerMethod);
此方法执行完成后已经完成了异常处理方法的调用,若方法返回值为视图ModelAndView或其他视图类型,则还需要借助视图解析器如InternalResourceViewResolver
对视图进行解析渲染,若为其他类型的值则将值写入到response响应中。
2. demo
Controller类方法:
@Controller
@RequestMapping(value = "test")
public class HelloWorldController{
@Data
public static class User {
private String username;
private Integer age;
private String address;
}
@RequestMapping(value = "user/get", method = RequestMethod.POST)
@ResponseBody
public Object testObject(@RequestBody @Valid User user, @RequestParam String address) {
user.setAddress(address);
// 这里特意抛出RuntimeException异常
throw new RuntimeException("this is a exception");
}
}
ExceptionHandlerController异常处理类
@ControllerAdvice
@ResponseBody
public class ExceptionHandlerController {
@ExceptionHandler(value = Exception.class)
public Object handleException(Exception e) {
return CommonResult.fail("Exception:" + e.getMessage());
}
@ExceptionHandler(value = RuntimeException.class)
public Object handlerRuntimeException(Exception e) {
return CommonResult.fail("handlerRuntimeException:" + e.getMessage());
}
}
ExceptionHandlerController类中定义了两个异常处理方法,一个处理Exception异常,一个处理RuntimeException异常,那个根据controller方法抛出的异常RuntimeException再结合上面的分析(RuntimeException到RuntimeException深度为0,RuntimeException到Exception中间继承了一次深度为1)可以得出抛出异常类型的处理方法为handlerRuntimeException
方法。 运行程序结果如下:
到此这篇关于详解SpringMVC中的异常处理机制的文章就介绍到这了,更多相关SpringMVC异常处理内容请搜索编程网以前的文章或继续浏览下面的相关文章希望大家以后多多支持编程网!