如何结合适配器与外观模式实现多数据库适配工具？

核心设计思路 #

采用抽象工厂模式+策略模式组合实现，配合依赖注入完成数据库类型的动态切换，既能满足当前MySQL、PostgreSQL的支持需求，也能轻松扩展后续新增的数据库类型。

步骤1：定义统一接口层 #

1.1 数据库操作接口（规范所有数据库行为） #

public interface DatabaseOperations {
    List<String> getAllDatabases(Connection connection) throws SQLException;
    // 后续可按需添加其他操作接口，比如getTables、executeCustomQuery等
}

1.2 数据库连接器接口（负责连接创建与操作实例获取） #

public interface DatabaseConnector {
    Connection getConnection(DatabaseModel db) throws IOException, SQLException;
    DatabaseOperations getDatabaseOperations();
}

步骤2：实现各数据库的具体类 #

2.1 PostgreSQL实现 #

操作类

public class PostgresDatabaseOperations implements DatabaseOperations {
    @Override
    public List<String> getAllDatabases(Connection connection) throws SQLException {
        List<String> databases = new ArrayList<>();
        try (PreparedStatement stmt = connection.prepareStatement(
                "SELECT datname FROM pg_database WHERE datistemplate = false;")) {
            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                databases.add(rs.getString("datname"));
            }
        }
        return databases;
    }
}

连接器类

public class PostgresConnector implements DatabaseConnector {
    @Override
    public Connection getConnection(DatabaseModel db) throws IOException, SQLException {
        // 实现PostgreSQL连接逻辑
        String url = String.format("jdbc:postgresql://%s:%d/", db.getHost(), db.getPort());
        return DriverManager.getConnection(url, db.getUsername(), db.getPassword());
    }

    @Override
    public DatabaseOperations getDatabaseOperations() {
        return new PostgresDatabaseOperations();
    }
}

2.2 MySQL实现 #

操作类

public class MySqlDatabaseOperations implements DatabaseOperations {
    @Override
    public List<String> getAllDatabases(Connection connection) throws SQLException {
        List<String> databases = new ArrayList<>();
        try (PreparedStatement stmt = connection.prepareStatement("SHOW DATABASES;")) {
            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                databases.add(rs.getString(1));
            }
        }
        return databases;
    }
}

连接器类

public class MySqlConnector implements DatabaseConnector {
    @Override
    public Connection getConnection(DatabaseModel db) throws IOException, SQLException {
        // 实现MySQL连接逻辑
        String url = String.format("jdbc:mysql://%s:%d/", db.getHost(), db.getPort());
        return DriverManager.getConnection(url, db.getUsername(), db.getPassword());
    }

    @Override
    public DatabaseOperations getDatabaseOperations() {
        return new MySqlDatabaseOperations();
    }
}

步骤3：创建工厂类（替代原BaseAdapter的switch逻辑） #

用工厂类统一管理连接器创建，避免硬编码switch，扩展新数据库时仅需新增Connector并更新工厂类即可。

public class DatabaseConnectorFactory {
    public static DatabaseConnector getConnector(String serverType) {
        return switch (serverType.toLowerCase()) {
            case "postgres" -> new PostgresConnector();
            case "mysql" -> new MySqlConnector();
            default -> throw new IllegalArgumentException("不支持的数据库类型: " + serverType);
        };
    }
}

步骤4：修改控制器与Service层 #

Service层接口（原migrationInterface） #

public interface MigrationService {
    List<String> getAllDatabases(DatabaseModel db) throws IOException, SQLException;
}

Service实现类 #

public class MigrationServiceImpl implements MigrationService {
    @Override
    public List<String> getAllDatabases(DatabaseModel db) throws IOException, SQLException {
        DatabaseConnector connector = DatabaseConnectorFactory.getConnector(db.getServerType());
        try (Connection connection = connector.getConnection(db)) {
            return connector.getDatabaseOperations().getAllDatabases(connection);
        }
    }
}

控制器修改（保留原有接口，简化内部逻辑） #

@PostMapping("/allDatabases")
public List<String> getDatabases(@RequestBody DatabaseModel db) 
    throws IOException, SQLException {
    
    return migrationService.getAllDatabases(db);
}

扩展新数据库的方式 #

1. 新增对应数据库的DatabaseOperations实现类，编写专属SQL逻辑
2. 新增对应数据库的DatabaseConnector实现类，实现连接逻辑并返回操作类实例
3. 在DatabaseConnectorFactory的switch分支中添加新的数据库类型判断

额外优化建议 #

• 用枚举定义支持的数据库类型，避免字符串硬编码错误
• 结合Spring依赖注入，将各Connector注册为Bean，工厂类直接从容器获取实例，进一步解耦
• 将SQL语句抽离到配置文件，方便维护与修改

内容的提问来源于stack exchange，提问作者Nisha