Generic response error handling using @ControllerAdvice

CustomResponseEntityExceptionHandler.java

@ControllerAdvice
public class CustomResponseEntityExceptionHandler extends ResponseEntityExceptionHandler {

    @Override
    protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
        List<FieldError> fieldErrors = ex.getBindingResult().getFieldErrors();
        List<ObjectError> globalErrors = ex.getBindingResult().getGlobalErrors();
        List<String> errors = new ArrayList<>(fieldErrors.size() + globalErrors.size());
        String error;
        for (FieldError fieldError : fieldErrors) {
            error = fieldError.getField() + ", " + fieldError.getDefaultMessage();
            errors.add(error);
        }
        for (ObjectError objectError : globalErrors) {
            error = objectError.getObjectName() + ", " + objectError.getDefaultMessage();
            errors.add(error);
        }
        ErrorMessage errorMessage = new ErrorMessage(errors);
        return new ResponseEntity(errorMessage, headers, status);
    }

    @Override
    protected ResponseEntity<Object> handleHttpMediaTypeNotSupported(HttpMediaTypeNotSupportedException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
        String unsupported = "Unsupported content type: " + ex.getContentType();
        String supported = "Supported content types: " + MediaType.toString(ex.getSupportedMediaTypes());
        ErrorMessage errorMessage = new ErrorMessage(unsupported, supported);
        return new ResponseEntity(errorMessage, headers, status);
    }

    @Override
    protected ResponseEntity<Object> handleHttpMessageNotReadable(HttpMessageNotReadableException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
        Throwable mostSpecificCause = ex.getMostSpecificCause();
        ErrorMessage errorMessage;
        if (mostSpecificCause != null) {
            String exceptionName = mostSpecificCause.getClass().getName();
            String message = mostSpecificCause.getMessage();
            errorMessage = new ErrorMessage(exceptionName, message);
        } else {
            errorMessage = new ErrorMessage(ex.getMessage());
        }
        return new ResponseEntity(errorMessage, headers, status);
    }
}

ErrorMessage.java

@XmlRootElement
public class ErrorMessage {

    private List<String> errors;

    public ErrorMessage() {
    }

    public ErrorMessage(List<String> errors) {
        this.errors = errors;
    }

    public ErrorMessage(String error) {
        this(Collections.singletonList(error));
    }

    public ErrorMessage(String ... errors) {
        this(Arrays.asList(errors));
    }

    public List<String> getErrors() {
        return errors;
    }

    public void setErrors(List<String> errors) {
        this.errors = errors;
    }
}

GlobalControllerExceptionHandler.java

@ControllerAdvice
class GlobalControllerExceptionHandler {

    @ExceptionHandler
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    @ResponseBody
    ErrorMessage handleException(MethodArgumentNotValidException ex) {
        List<FieldError> fieldErrors = ex.getBindingResult().getFieldErrors();
        List<ObjectError> globalErrors = ex.getBindingResult().getGlobalErrors();
        List<String> errors = new ArrayList<>(fieldErrors.size() + globalErrors.size());
        String error;
        for (FieldError fieldError : fieldErrors) {
            error = fieldError.getField() + ", " + fieldError.getDefaultMessage();
            errors.add(error);
        }
        for (ObjectError objectError : globalErrors) {
            error = objectError.getObjectName() + ", " + objectError.getDefaultMessage();
            errors.add(error);
        }
        return new ErrorMessage(errors);
    }

    @ExceptionHandler
    @ResponseStatus(HttpStatus.UNSUPPORTED_MEDIA_TYPE)
    @ResponseBody
    ErrorMessage getErrorMessage(HttpMediaTypeNotSupportedException ex) {
        String unsupported = "Unsupported content type: " + ex.getContentType();
        String supported = "Supported content types: " + MediaType.toString(ex.getSupportedMediaTypes());
        return new ErrorMessage(unsupported, supported);
    }

    @ExceptionHandler
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    @ResponseBody
    ErrorMessage getErrorMessage(HttpMessageNotReadableException ex) {
        Throwable mostSpecificCause = ex.getMostSpecificCause();
        if (mostSpecificCause != null) {
            String exceptionName = mostSpecificCause.getClass().getName();
            String message = mostSpecificCause.getMessage();
            return new ErrorMessage(exceptionName, message);
        }
        return new ErrorMessage(ex.getMessage());
    }
}

GlobalControllerExceptionHandlerExample.java

@ControllerAdvice
class GlobalControllerExceptionHandler {
    
    @ExceptionHandler
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    @ResponseBody
    ErrorMessage handleException(SomeException ex) {
        ErrorMessage errorMessage = createErrorMessage(ex);
        return errorMessage;
    }

    @ExceptionHandler
    @ResponseStatus(HttpStatus.GONE)
    @ResponseBody
    ErrorMessage handleException(OtherException ex) {
        ErrorMessage errorMessage = createErrorMessage(ex);
        return errorMessage;
    }   
}

validationerror.json

{
    "errors": [
        "name, may not be empty",
        "email, not a well-formed email address"
    ]
}