if else准備好的聲明

Question

我正試圖在if else中使用預准備語句。 可悲的是，我得到的索引1超出了范圍。 添加了一些細節...我的代碼：

try {
        String query = "select * from dbo.Table";
        String width = jFormattedTextField1.getText();
        String heigth = jFormattedTextField2.getText();
        PreparedStatement ps;

        if (width.equals("") && heigth.equals("")) {
            query = "select * from dbo.Table ";
        } else if (width != null && !"".equals(width) && heigth != null && !"".equals(heigth)) {
            query += "where width = ? and heigth = ?";
            ps = conn.prepareStatement(query);
            ps.setString(1, width);
            ps.setString(2, heigth);
        } else if (width != null && heigth.equals("")){
            query += "where width = " + width;
            ps = conn.prepareStatement(query);
        } else {
        query += "where heigth = " + heigth;
        ps = conn.prepareStatement(query);
    }
        ps = conn.prepareStatement(query);
        ResultSet rs = ps.executeQuery();
        jTable1.setModel(DbUtils.resultSetToTableModel(rs));
    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, e, "ERROR", JOptionPane.ERROR_MESSAGE);
    }

Answer 1

初始化SQL String后，您應該創建PreparedStatement ，這意味着它必須在if-else主體內完成。

        String width = jFormattedTextField1.getText();
        String heigth = jFormattedTextField2.getText();
        PreparedStatement ps;
        if (width.equals("") && heigth.equals("")) {
            query = "select * from dbo.Table ";
            ps = conn.prepareStatement(query);
        } else if (width != null && !"".equals(width) && heigth != null && !"".equals(heigth)) {
            query = "select * from dbo.Table where width = ? and heigth = ?";
            ps = conn.prepareStatement(query);
            ps.setString(1, width);
            ps.setString(2, heigth);
        }

您還應該在else子句中初始化PreparedStatement ，以確保在執行它之前初始化它。

編輯：

查看更新的代碼，您在最后兩種情況下濫用PreparedStatement 。 我建議：

try {
    String query = "select * from dbo.Table";
    String width = jFormattedTextField1.getText();
    String height = jFormattedTextField2.getText();
    PreparedStatement ps;

    if (width.equals("") && height.equals("")) {
        ps = conn.prepareStatement(query);
    } else if (width != null && !"".equals(width) && height != null && !"".equals(height)) {
        query += " where width = ? and height = ?";
        ps = conn.prepareStatement(query);
        ps.setString(1, width);
        ps.setString(2, height);
    } else if (width != null && height.equals("")){
        query += " where width = ?";
        ps = conn.prepareStatement(query);
        ps.setString(1, width);

    } else {
        query += " where height = ?";
        ps = conn.prepareStatement(query);
        ps.setString(1, height);
    }
    ResultSet rs = ps.executeQuery();
    jTable1.setModel(DbUtils.resultSetToTableModel(rs));
} catch (Exception e) {
    JOptionPane.showMessageDialog(null, e, "ERROR", JOptionPane.ERROR_MESSAGE);
}

Answer 2

初始化SQL字符串后創建預准備語句。 謝謝