Spring ControllerAdvice - 无法覆盖 ResponseEntityExceptionHandler 中的 handleHttpRequestMethodNotSupported()

Question

以下是我目前面临的情况的一些事实

1. 我最近为 Spring RestController构建了一个RestControllerAdvice具有各种ExceptionHandler全局异常处理程序的函数。

2. 由于我想返回我的自定义响应 json 以处理 中指定的预定义 HTTP 错误ResponseEntityExceptionHandler，因此我的RestControllerAdvice类继承了，并且覆盖了, 之类的ResponseEntityExceptionHandler方法。handleHttpRequestMethodNotSupported()handleHttpMessageNotReadable()

3. 我已经成功覆盖handleHttpMediaTypeNotSupported()，handleHttpMessageNotReadable()但是当涉及到时handleHttpRequestMethodNotSupported()，我没有这样做。

这是我的代码的摘录：

@Order(Ordered.HIGHEST_PRECEDENCE)
@RestControllerAdvice(annotations=RestController.class)
public class TestRestExceptionHandler extends ResponseEntityExceptionHandler{

    @Override
    protected ResponseEntity<Object> handleHttpRequestMethodNotSupported(HttpRequestMethodNotSupportedException ex, HttpHeaders headers, HttpStatus status, WebRequest request){
        BaseResponseJson response = new BaseResponseJson();
        response.setRespCode(BaseResponseJson.JSON_RESP_CODE_ERROR);
        response.setRespMsg("Request Method Not Supported");
        return handleExceptionInternal(ex, response, headers, status, request);
    }

    @Override
    protected ResponseEntity<Object> handleHttpMessageNotReadable(HttpMessageNotReadableException ex, HttpHeaders headers, HttpStatus status, WebRequest request){
        BaseResponseJson response = new BaseResponseJson();
        response.setRespCode(BaseResponseJson.JSON_RESP_CODE_ERROR);
        response.setRespMsg("Message Not Readable");
        return handleExceptionInternal(ex, response, headers, status, request);
    }

    @Override
    protected ResponseEntity<Object> handleHttpMediaTypeNotSupported(HttpMediaTypeNotSupportedException ex, HttpHeaders headers, HttpStatus status, WebRequest request){
        BaseResponseJson response = new BaseResponseJson();
        response.setRespCode(BaseResponseJson.JSON_RESP_CODE_ERROR);
        response.setRespMsg("Media Type Not Supported");
        return handleExceptionInternal(ex, response, headers, status, request);
    }
}

日志handleHttpRequestMethodNotSupported()显示如下：

[2019-06-05T17:49:50.368+0800][XNIO-74 task-7][WARN ][o.s.w.s.m.s.DefaultHandlerExceptionResolver] Resolved exception caused by Handler execution: org.springframework.web.HttpRequestMethodNotSupportedException: Request method 'GET' not supported

日志handleHttpMessageNotReadable()显示如下：

[2019-06-05T17:50:21.915+0800][XNIO-74 task-8][WARN ][o.s.w.s.m.m.a.ExceptionHandlerExceptionResolver] Resolved exception caused by Handler execution

如您所见，成功代码由 处理，ExceptionHandlerExceptionResolver而故障代码由 处理DefaultHandlerExceptionResolver。

我想知道根本原因是什么，如果有人可以推荐任何可用的解决方案，我将不胜感激。谢谢你。

Answer 1

从jackycflau 的回答中，我们可以总结为 2 个问题。

一季度。为什么删除annotations=RestController.class将适用于 HttpRequestMethodNotSupportedException

Q2。为什么只有HttpRequestMethodNotSupportedException没有被抓住？

要回答这两个问题，我们需要看一下 spring 如何处理异常的代码。以下源码基于spring 4.3.5。

在 springDispatcherServlet处理请求期间，当发生错误时，HandlerExceptionResolver将尝试解决异常。在给定的情况下，异常被委托给ExceptionHandlerExceptionResolver。判断用哪种方法解决异常的方法是（getExceptionHandlerMethod在ExceptionHandlerExceptionResolver.java第417行）

/**
 * Find an {@code @ExceptionHandler} method for the given exception. The default
 * implementation searches methods in the class hierarchy of the controller first
 * and if not found, it continues searching for additional {@code @ExceptionHandler}
 * methods assuming some {@linkplain ControllerAdvice @ControllerAdvice}
 * Spring-managed beans were detected.
 * @param handlerMethod the method where the exception was raised (may be {@code null})
 * @param exception the raised exception
 * @return a method to handle the exception, or {@code null}
 */
protected ServletInvocableHandlerMethod getExceptionHandlerMethod(HandlerMethod handlerMethod, Exception exception) {
    Class<?> handlerType = (handlerMethod != null ? handlerMethod.getBeanType() : null);

    if (handlerMethod != null) {
        ExceptionHandlerMethodResolver resolver = this.exceptionHandlerCache.get(handlerType);
        if (resolver == null) {
            resolver = new ExceptionHandlerMethodResolver(handlerType);
            this.exceptionHandlerCache.put(handlerType, resolver);
        }
        Method method = resolver.resolveMethod(exception);
        if (method != null) {
            return new ServletInvocableHandlerMethod(handlerMethod.getBean(), method);
        }
    }

    for (Entry<ControllerAdviceBean, ExceptionHandlerMethodResolver> entry : this.exceptionHandlerAdviceCache.entrySet()) {
        if (entry.getKey().isApplicableToBeanType(handlerType)) {
            ExceptionHandlerMethodResolver resolver = entry.getValue();
            Method method = resolver.resolveMethod(exception);
            if (method != null) {
                return new ServletInvocableHandlerMethod(entry.getKey().resolveBean(), method);
            }
        }
    }

    return null;
}

由于我们正在使用@RestControllerAdvice，我们只需要关注 for 循环，它决定ControllerAdviceBean使用哪个。我们可以看到该方法isApplicableToBeanType会判断是否ControllerAdviceBean适用，相关代码为（ControllerAdviceBean.java第149行）

/**
 * Check whether the given bean type should be assisted by this
 * {@code @ControllerAdvice} instance.
 * @param beanType the type of the bean to check
 * @see org.springframework.web.bind.annotation.ControllerAdvice
 * @since 4.0
 */
public boolean isApplicableToBeanType(Class<?> beanType) {
    if (!hasSelectors()) {
        return true;
    }
    else if (beanType != null) {
        for (String basePackage : this.basePackages) {
            if (beanType.getName().startsWith(basePackage)) {
                return true;
            }
        }
        for (Class<?> clazz : this.assignableTypes) {
            if (ClassUtils.isAssignable(clazz, beanType)) {
                return true;
            }
        }
        for (Class<? extends Annotation> annotationClass : this.annotations) {
            if (AnnotationUtils.findAnnotation(beanType, annotationClass) != null) {
                return true;
            }
        }
    }
    return false;
}

private boolean hasSelectors() {
    return (!this.basePackages.isEmpty() || !this.assignableTypes.isEmpty() || !this.annotations.isEmpty());
}

通过阅读代码，我们可以解释发生了什么：

回答 Q1

当annotations=RestController.class被删除时，hasSelectors将返回 false，因此isApplicableToBeanType将返回 true。所以在这种情况下HttpRequestMethodNotSupportedException会被处理TestRestExceptionHandler。

回答 Q2

对于HttpRequestMethodNotSupportedException，DispatcherSerlvet找不到处理请求的控制器方法。因此handlerMethod传递给getExceptionHandlerMethodis null，然后beanType传递给isApplicableToBeanType也是 null 并返回 false 。

另一方面，DispatcherSerlvet可以找到HttpMessageNotReadableExceptionor 的控制器方法HttpMediaTypeNotSupportedException。因此，其余控制器处理程序方法将被传递给getExceptionHandlerMethod并isApplicableToBeanType返回 true。