组合框中的错误：java.sql.SQLException：无效的游标状态 - 没有当前行

Question

我一直收到这个错误。

我有一个填充了数据库元素的组合框，我希望它能使所选选项出现在文本框中，但是我收到了这个错误。它仅适用于第一个结果：

这是代码：

private void cmbx_vendActionPerformed(java.awt.event.ActionEvent evt) {                                          
    // TODO add your handling code here:
   try{
      String url = "jdbc:informix-sqli://192.168.2.3:1525/cubo:INFORMIXSERVER=myserver;user=infx;password=infx";
    Connection con1 = DriverManager.getConnection(url);  
    System.out.println("Cubo conectada combobox");
    Statement st1= con1.createStatement();
    ResultSet rs1=st1.executeQuery("SELECT * FROM cartsusc WHERE vendedor = '"+this.cmbx_vend.getSelectedItem()+"'");
    rs1.next();
    this.txt_dato.setText(rs1.getString("vendedor"));

    }
    catch(Exception e){
        JOptionPane.showMessageDialog(null, e);
    }
}

Answer 1

你必须使用：

if(rs1.next()){
    this.txt_dato.setText(rs1.getString("vendedor"));
}

不要像这样设置参数，这可能会导致语法错误或SQL注入，相反，您必须使用PreparedStatement作为示例：

String query = "SELECT * FROM cartsusc WHERE vendedor = ?";
try (PreparedStatement pstm = connection.prepareStatement(query)) {

    pstm.setString(1, this.cmbx_vend.getSelectedItem());
    ResultSet rs1 = pstm.executeQuery();
    if(rs1.next()){
       this.txt_dato.setText(rs1.getString("vendedor"));
       //this.txt_dato.setText(rs1.getString(1));//or you can get your result like this
    }
}

完成后别忘了关闭你的陈述和联系。

Answer 2

检查ResultSet#next()以查看是否确实有一行可用。

另外，请始终使用PreparedStatement。它们有助于降低SQL注入攻击的风险。

通常的习语是：

try {
    Connection conn = getConnection();
    try {
        String sql = "SELECT * FROM cartsusc WHERE vendedor = ?";
        PreparedStatement ps = conn.prepareStatement(sql);
        try {
            ps.setString(1, this.cmbx_vend.getSelectedItem());
            ResultSet rs = ps.executeQuery();
            try {
                if (rs.next()) {
                    this.txt_dato.setText(rs1.getString("vendedor"));
                }
            } finally {
                rs.close();
            }
        } finally {
            ps.close();
        }
    } finally {
        conn.close();
    }
} catch (SQLException e) {
    //handle
}

从Java 7开始，您可以使用try-with-resources自动关闭资源：

String sql = "SELECT * FROM cartsusc WHERE vendedor = ?";
try (
    Connection conn = getConnection();
    PreparedStatement ps = conn.prepareStatement(sql);
    ) {
    ps.setString(1, this.cmbx_vend.getSelectedItem());
    try (ResultSet rs = ps.executeQuery()) {
        if (rs.next()) {
            this.txt_dato.setText(rs1.getString("vendedor"));
        }
    }
} catch (SQLException e) {
    //handle
}