SpringBoot :在RestController响应中展开子对象

@RestController
public class UserController {

    @GetMapping("/user")
    public User getUser() {
        User user = new User();
        user.setId(1);
        user.setName("John Doe");
        
        Address address = new Address();
        address.setCity("New York");
        address.setCountry("USA");
        
        user.setAddress(address);
        
        return user;
    }
}

public class User {
    private int id;
    private String name;
    private Address address;
    
    // getters and setters
}

public class Address {
    private String city;
    private String country;
    
    // getters and setters
}