问Eclipse Maven Rest Api:错误:无法将UserNotFoundException解析为类型。如何解决这个问题？

EN

@RestController
public class UserResource {
    
    //GET /users/{id}
    //retrieveUser(int id)
    @GetMapping("/users/{id}")
    public User retrieveUser(@PathVariable int id) {
        User user = service.findone(id);
        if(user==null)
            throw new UserNotFoundException("id-"+ id); //this throwing the error.
        return user;
    }
    
}