Enable server-side validation
Validation on server side has been removed in the Angular version. PetValidator is disabled. You may save a pet with an empty name despite the @Size(min = 1) String name on PetRequest inner class. You may do a test :
curl -H "Content-Type: application/json" -X PUT -d '{"id":1,"name":"","birthDate":"2010-09-07","typeId":"1"}' http://localhost:8080/api/customer/owners/1/pets/1
More over, duplicate names are not handled.
Check the Spring Petclinic ReactJS version. Errors are correctly handled: https://github.com/spring-petclinic/spring-petclinic-reactjs See classes: InvalidRequestException, ApiExceptionHandler, ErrorResource, FieldErrorResource
I set up the webapplication without doing any modification on it and tried out your cURL-command, but got the following return:
{"timestamp":1496911194455,"status":404,"error":"Not Found","message":"No message available","path":"/api/customer/owners/1/pets/1"}
Trying to do the change you proposed directly in the GUI, I am able to add Pet instances with a single whitespace as name, but not with an entirely empty ("") name.