環境準備

1. Oracle JDBC 驅動 JAR (`ojdbc8.jar` / `ojdbc11.jar`) 放入 `WEB-INF/lib` 或伺服器共享庫。
2. Servlet 容器 (Tomcat/Jetty) 配置資料源 (JNDI) 或直接在 Servlet 載入驅動。

Servlet 完整代碼

@WebServlet("/dbQuery")
public class OracleQueryServlet extends HttpServlet {
    private static final String DRIVER = "oracle.jdbc.OracleDriver";
    private static final String URL = "jdbc:oracle:thin:@192.168.1.6:1521:PC6";
    private static final String USER = "ndb";
    private static final String PASS = "ndb";

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {

        resp.setContentType("text/html;charset=UTF-8");
        PrintWriter out = resp.getWriter();

        out.println("");
        out.println("
資料查詢結果
");

        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

        try {
            // 1. 載入驅動 (JDBC 4.0+ 可省略)
            Class.forName(DRIVER);

            // 2. 建立連線
            conn = DriverManager.getConnection(URL, USER, PASS);

            // 3. 執行查詢
            stmt = conn.createStatement();
            String sql = "SELECT * FROM DATA";
            rs = stmt.executeQuery(sql);

            // 4. 顯示結果 (HTML 表格)
            ResultSetMetaData meta = rs.getMetaData();
            int colCount = meta.getColumnCount();

            out.println("");
            out.print("");
            for (int i = 1; i <= colCount; i++) out.print("");
            out.println("");

            int rowCount = 0;
            while (rs.next() && rowCount < 100) { // 限制顯示筆數
                out.print("");
                for (int i = 1; i <= colCount; i++) out.print("");
                out.println("");
                rowCount++;
            }
            out.println("
" + meta.getColumnLabel(i) + "
" + rs.getString(i) + "
");
            out.println("
共顯示 " + rowCount + " 筆資料
");

        } catch (ClassNotFoundException e) {
            out.println("
驅動類未找到: " + e.getMessage() + "
");
        } catch (SQLException e) {
            out.println("
資料庫錯誤: " + e.getMessage() + "
");
        } finally {
            // 5. 關閉資源 (逆序)
            closeQuietly(rs);
            closeQuietly(stmt);
            closeQuietly(conn);
        }
        out.println("");
    }

    private void closeQuietly(AutoCloseable c) {
        try { if (c != null) c.close(); } catch (Exception ignored) {}
    }
}

關鍵點與最佳實踐

現代化架構建議

• Spring Boot + MyBatis/JPA：資料源自動配置、Mapper 介面、事務註解、分頁插件。
• Reactive (R2DBC) + WebFlux：非阻塞資料庫存取，適合高併發。
• 避免在 Servlet 直接寫 JDBC，分層架構 (Controller → Service → Repository) 利於測試與維護。