java之jdbc_採用PreparedStatement根據條件查詢

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import java.sql.*;

//採用PreparedStatement根據條件查詢
public class QueryTest05 {
    public static void main(String[] args) {
        if (args.length == 0) {
            throw new IllegalArgumentException("參數非法，正確使用爲： Java QueryTest05 + 參數");
        }

        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            //第一步，加載數據庫驅動，不一樣的數據庫驅動程序不同
            Class.forName("oracle.jdbc.driver.OracleDriver");
            //第二部，獲得數據庫鏈接
            String dburl = "jdbc:oracle:thin:@localhost:1521:orcl";
            //String dburl = "jdbc:oracle:thin:@192.168.21.1:1521:orcl";
            //String dburl = "jdbc:oracle:thin:@127.0.0.1:1521:orcl";
            String userName = "system";
            String password = "wanwan";
            conn = DriverManager.getConnection(dburl, userName, password);
            //System.out.println(conn);

            //第三步，獲得PreparedStatement,執行sql
            //採用PreparedStatement不建議採用拼串的方式
            //由於拼串每次的SQL語句不同，這樣就沒有利用PreparedStatement的優勢
            //仍然每次都編譯，和Statement沒什麼差異
            //String sql = "select * from tb_student where sex like '" + args[0] + "'";
            //pstmt = conn.prepareStatement(sql);

            //建議採用佔位符的方式
            //這樣每次SQL語句是同樣的，數據庫就不會再編譯
            //這樣就利用了PreparedStatement的優勢，顯著地提升性能
            //瞭解Statement和PreparedStatement的區別
            String sql = "select * from tb_student where sex like ?";
            pstmt = conn.prepareStatement(sql);
            //注意：此處不要加單引號
            pstmt.setString(1, args[0]);
            //第四部，取得結果集
            //將條件作爲sql語句的一部分進行拼接
            //注意字符串必須採用單引號引發來
            rs = pstmt.executeQuery();
            //System.out.println("sql" + sql);
            while (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                System.out.println(id + " , " + name);
            }


        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //注意關閉原則：從裏到外


            try {
                if (rs != null) {
                rs.close();
                }
                if (pstmt != null) {
                    pstmt.close();
                }
                if (conn != null) {
                    conn.close();
                }
            } catch(SQLException e) {

            }

        }
    }
}