对于 Spring Boot，我不完全确定为什么这是必要的（尽管 @ResponseBody 是在 @ExceptionHandler 上定义的，但我得到了 /error 后备），但以下内容本身不起作用：
@ResponseBody
@ResponseStatus(HttpStatus.BAD_REQUEST)
@ExceptionHandler(IllegalArgumentException.class)
public ErrorMessage handleIllegalArguments(HttpServletRequest httpServletRequest, IllegalArgumentException e) {
log.error("Illegal arguments received.", e);
ErrorMessage errorMessage = new ErrorMessage();
errorMessage.code = 400;
errorMessage.message = e.getMessage();
return errorMessage;
}
它仍然抛出异常，显然是因为没有可生产的媒体类型被定义为请求属性：
// AbstractMessageConverterMethodProcessor
@SuppressWarnings("unchecked")
protected <T> void writeWithMessageConverters(T value, MethodParameter returnType,
ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
Class<?> valueType = getReturnValueType(value, returnType);
Type declaredType = getGenericType(returnType);
HttpServletRequest request = inputMessage.getServletRequest();
List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(request);
List<MediaType> producibleMediaTypes = getProducibleMediaTypes(request, valueType, declaredType);
if (value != null && producibleMediaTypes.isEmpty()) {
throw new IllegalArgumentException("No converter found for return value of type: " + valueType); // <-- throws
}
// ....
@SuppressWarnings("unchecked")
protected List<MediaType> getProducibleMediaTypes(HttpServletRequest request, Class<?> valueClass, Type declaredType) {
Set<MediaType> mediaTypes = (Set<MediaType>) request.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
if (!CollectionUtils.isEmpty(mediaTypes)) {
return new ArrayList<MediaType>(mediaTypes);
所以我添加了它们。
@ResponseBody
@ResponseStatus(HttpStatus.BAD_REQUEST)
@ExceptionHandler(IllegalArgumentException.class)
public ErrorMessage handleIllegalArguments(HttpServletRequest httpServletRequest, IllegalArgumentException e) {
Set<MediaType> mediaTypes = new HashSet<>();
mediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
httpServletRequest.setAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, mediaTypes);
log.error("Illegal arguments received.", e);
ErrorMessage errorMessage = new ErrorMessage();
errorMessage.code = 400;
errorMessage.message = e.getMessage();
return errorMessage;
}
这让我通过了“支持的兼容媒体类型”，但它仍然无法正常工作，因为我的ErrorMessage 有问题：
public class ErrorMessage {
int code;
String message;
}
JacksonMapper 没有把它当成“可转换”来处理，所以我只好加了getter/setter，还加了@JsonProperty注解
public class ErrorMessage {
@JsonProperty("code")
private int code;
@JsonProperty("message")
private String message;
public int getCode() {
return code;
}
public void setCode(int code) {
this.code = code;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
}
然后我按预期收到了我的消息
{"code":400,"message":"An \"url\" parameter must be defined."}