如何使用存储库模式模拟MongoDB数据访问层？

public interface UserRepository {
    void save(User user);
    void delete(String id);
    User findById(String id);
    List<User> findAll();
}

public class MongoUserRepository implements UserRepository {
    private MongoClient mongoClient;
    private MongoDatabase database;
    private MongoCollection<Document> collection;

    public MongoUserRepository() {
        // 初始化MongoDB连接
        mongoClient = new MongoClient("localhost", 27017);
        database = mongoClient.getDatabase("mydb");
        collection = database.getCollection("users");
    }

    @Override
    public void save(User user) {
        // 将User对象转换为MongoDB的文档格式，并插入到集合中
        Document document = new Document("id", user.getId())
                .append("name", user.getName())
                .append("email", user.getEmail());
        collection.insertOne(document);
    }

    @Override
    public void delete(String id) {
        // 根据id删除对应的文档
        collection.deleteOne(eq("id", id));
    }

    @Override
    public User findById(String id) {
        // 根据id查询对应的文档，并将其转换为User对象
        Document document = collection.find(eq("id", id)).first();
        if (document != null) {
            return new User(document.getString("id"),
                    document.getString("name"),
                    document.getString("email"));
        }
        return null;
    }

    @Override
    public List<User> findAll() {
        // 查询所有文档，并将其转换为User对象列表
        List<User> users = new ArrayList<>();
        collection.find().forEach((Consumer<Document>) document -> {
            users.add(new User(document.getString("id"),
                    document.getString("name"),
                    document.getString("email")));
        });
        return users;
    }
}

public class UserService {
    private UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public void createUser(User user) {
        // 调用存储库接口的save方法保存用户
        userRepository.save(user);
    }

    public User findUserById(String id) {
        // 调用存储库接口的findById方法查询用户
        return userRepository.findById(id);
    }

    public List<User> findAllUsers() {
        // 调用存储库接口的findAll方法查询所有用户
        return userRepository.findAll();
    }

    public void deleteUser(String id) {
        // 调用存储库接口的delete方法删除用户
        userRepository.delete(id);
    }
}