PersonController.groovy

@Post("/save")
HttpResponse<Map> savePerson(@Body Person person) {
    try {
        return HttpResponse.ok( [ person: personService.save(person) ] as Map )
    }
    catch(ValidationException e) {
        return HttpResponse.unprocessableEntity().body(
                [
                        person: person,
                        errors: e.errors.allErrors.collect {
                            FieldError err = it as FieldError
                            [
                                    field: err.field,
                                    rejectedValue: err.rejectedValue,
                                    message: err.defaultMessage
                            ]
                        }
                ]
        ) as HttpResponse<Map>
    }
}