This is happening due to the @Controller annotation. By default controller annotation return the view in spring. If your application is getting and returning json better to use @RestController annotation that is return json response by default

  @RestController
public class UserController {

@Autowired
private UserService userService;



 @PostMapping("/user/add")


public void addNewUser(@RequestBody User user) throws BLException {
 userService.addNewUser(user);


}

}