實戰 JSP 進階編程之二：最簡單的 DAO 模式實現

DAO 模式四要素：介面、工廠、實現類、調用者。本文提供最簡單實現供初學者參考。

NewsDAO 介面

public interface NewsDAO {
  News getNewsByPrimaryKey(int newsid) throws SQLException;
  News[] getRecentNews();
  News[] getHotNews();
}

MySQL 實現類

public class NewsDAOMySQL implements NewsDAO {
  private String url = "jdbc:mysql://localhost:3306/joke?user=root";
  public NewsDAOMySQL() { /* 載入驅動 */ }
  public News getNewsByPrimaryKey(int newsid) throws SQLException {
    Connection conn = getConnection();
    Statement stmt = conn.createStatement();
    ResultSet rs = stmt.executeQuery("SELECT newsid,title,content FROM news2 WHERE newsid=" + newsid);
    News news = null;
    if (rs.next()) news = new News(rs.getInt(1), rs.getString(2), rs.getString(3));
    rs.close(); stmt.close(); conn.close();
    return news;
  }
  private Connection getConnection() throws SQLException {
    return DriverManager.getConnection(url);
  }
}

工廠類根據配置返回具體實現，調用者透過介面使用，實現資料庫切換解耦。