如何在使用Spring数据的mongodb中获取字段值列表作为结果

public interface UserRepository extends MongoRepository<User, String> {
    // 添加自定义的查询方法
    List<User> findByAge(int age);
}

spring.data.mongodb.host=your_host
spring.data.mongodb.port=your_port
spring.data.mongodb.database=your_database

@Document(collection = "users")
public class User {
    @Id
    private String id;
    private String name;
    private int age;
    // 其他字段和对应的getter/setter方法
}

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    public List<String> getUserNamesByAge(int age) {
        List<User> users = userRepository.findByAge(age);
        List<String> userNames = new ArrayList<>();
        for (User user : users) {
            userNames.add(user.getName());
        }
        return userNames;
    }
}