Handling of MethodArgumentNotValidException overridden by DefaultErrorAttributes - spring

Question

My goal is to have a custom response body for validation errors. This is a very common case and I've read lots of posts/blogs/articles and I've even implemented this myself in the past. For some reason, I cannot figure this out.
I have this #RestControllerAdvice
#Slf4j
#RequiredArgsConstructor
#RestControllerAdvice
public class ErrorHandler extends ResponseEntityExceptionHandler {
private final MessageSource messageSource;
#Override
protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex,
HttpHeaders headers, HttpStatus status, WebRequest request) {
ValidationErrorDTO validationError = ValidationErrorDTO.builder()
.fieldErrors(ex.getBindingResult().getFieldErrors().stream()
.map(fieldError -> FieldErrorDTO.builder()
.field(fieldError.getField())
.message(messageSource.getMessage(fieldError, LocaleContextHolder.getLocale()))
.build())
.collect(Collectors.toList()))
.build();
LOGGER.debug("W3MnsZ validation error: {}", validationError);
return new ResponseEntity<Object>(validationError, HttpStatus.BAD_REQUEST);
}
}
====
#ToString
#Builder
public class ValidationErrorDTO {
private final List<FieldErrorDTO> fieldErrors;
}
====
#ToString
#Builder
#Getter
#JsonInclude(Include.NON_NULL)
public class FieldErrorDTO {
private final String field;
private final String message;
}
My ErrorHandler.handleMethodArgumentNotValid() gets hit, but the actual response body returned to the client is not from my ValidationErrorDTO.
{
"timestamp": 1523115887261,
"status": 400,
"error": "Bad Request",
"exception": "org.springframework.web.bind.MethodArgumentNotValidException",
"errors": [
{
"codes": [
"NotEmpty.myDTO.field.another.lastly",
"NotEmpty.field.another.lastly",
"NotEmpty.lastly",
"NotEmpty.java.lang.String",
"NotEmpty"
],
"arguments": [
{
"codes": [
"myDTO.field.another.lastly",
"field.another.lastly"
],
"arguments": null,
"defaultMessage": "field.another.lastly",
"code": "field.another.lastly"
}
],
"defaultMessage": "may not be empty",
"objectName": "myDTO",
"field": "field.another.lastly",
"rejectedValue": null,
"bindingFailure": false,
"code": "NotEmpty"
}
],
"message": "Validation failed for object='myDTO'. Error count: 1",
"path": "/myPath"
}
I've figured out that what's happening is org.springframework.boot.autoconfigure.web.DefaultErrorAttributes is getting hit and somehow overriding my custom response body.
What do I do to allow my custom response body to be returned to the client?

Answer 1

Just figured it out.
ValidationErrorDTO.fieldErrors had no getter.
#ToString
#Builder
#Getter
public class ValidationErrorDTO {
#Singular
private final List<FieldErrorDTO> fieldErrors;
}
Now it works and we get response:
{
"fieldErrors": [
{
"field": "field.another.lastly",
"message": "may not be empty"
}
]
}