一、概述
在SpringMVC中,除了Filter和Interceptor拦截器外,还有对请求Controller的处理,即对请求和响应内容的处理和对请求参数的处理。
二、ControllerAdvice
@ControllerAdvice本质上同Component一样,因此也会被当成组件扫描。
其中@ExceptionHandler常用到。即抛出的异常会被统一拦截处理。在项目中对MethodArgumentNotValidException异常拦截处理
@ControllerAdvice
public class GlobalHandler {
@ExceptionHandler(MethodArgumentNotValidException.class)
public Result exceptionHandler(MethodArgumentNotValidException e) {
Result result = new Result(BizExceptionEnum.INVALID_REQ_PARAM.getErrorCode(),
BizExceptionEnum.INVALID_REQ_PARAM.getErrorMsg());
logger.error("req params error", e);
return result;
}
}
// 上述对MethodArgumentNotValidException异常统一拦截后并统一返回异常
实现原理:
public class DispatcherServlet extends FrameworkServlet {
// ......
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
// 处理所有异常
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
// ......
}
DispatcherServlet的initHandlerExceptionResolvers(context)方法,方法会取得所有实现了HandlerExceptionResolver接口的bean并保存起来,其中就有一个类型为ExceptionHandlerExceptionResolver的bean,这个bean在应用启动过程中会获取所有被@ControllerAdvice注解标注的bean对象做进一步处理,关键代码在这里
public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExceptionResolver
implements ApplicationContextAware, InitializingBean {
// ......
private void initExceptionHandlerAdviceCache() {
// ......
List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
AnnotationAwareOrderComparator.sort(adviceBeans);
for (ControllerAdviceBean adviceBean : adviceBeans) {
ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(adviceBean.getBeanType());
if (resolver.hasExceptionMappings()) {
// 找到所有ExceptionHandler标注的方法并保存成一个ExceptionHandlerMethodResolver类型的对象缓存起来
this.exceptionHandlerAdviceCache.put(adviceBean, resolver);
if (logger.isInfoEnabled()) {
logger.info("Detected @ExceptionHandler methods in " + adviceBean);
}
}
// ......
}
}
}
public ExceptionHandlerMethodResolver(Class<?> handlerType) {
// 查询当前类中@ExceptionHandler的方法
for (Method method : MethodIntrospector.selectMethods(handlerType, EXCEPTION_HANDLER_METHODS)) {
// 获取方法的异常类型
for (Class<? extends Throwable> exceptionType : detectExceptionMappings(method)) {
// 添加到缓存中
addExceptionMapping(exceptionType, method);
}
}
}
最后ExceptionHandler被执行过程
// 处理返回结果时,如果异常不为空,则进行异常处理
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) {
// ...
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
// 调用异常Handler处理
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// ...
}