having trouble display the name from my database

Question

I want to print the user name after logging in with his ID in another JFrame

I followed this method but it does not work

//this class to login
 public mClass() {
// Frame build :
        setSize(800, 600);
        setTitle(" page1  ");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        Toolkit toolkit = getToolkit();
        Dimension size = toolkit.getScreenSize();
        setLocation(size.width / 2 - getWidth() / 2,
                size.height / 3 - getHeight() / 3);
        //Panel & BackGround :
        JPanel panel = new JPanel();
        getContentPane().add(panel);
        panel.setLayout(null);
        panel.setBackground(Color.decode("#DFDDCE"));

        // text box
        JTextField user = new JTextField();
        user.setBounds(245, 300, 300, 40);
        user.setFont(newFonts);
        user.setForeground(Color.decode("#5195E1"));
        panel.add(user);
        // text for box :
        JLabel tx = new JLabel(" Enter your ID to login.");
        tx.setBounds(245, 30, size.width, size.height);
        panel.add(tx);
        //submit button :
        JButton login = new JButton(" login ");
        login.setBounds(245, 355, 300, 40);
        login.setBorder(new LineBorder(Color.decode("#5195E1")));
           login.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        try {
                            // Class.forName("com.mysql.jdbc.Driver");
                            String host = "jdbc:mysql://localhost:3306/mybase?serverTimezone=UTC";
                            String uName = "root"; String uPass = "dataroot";
                            Connection con = DriverManager.getConnection(host, uName, uPass);
                            String password=user.getText();
                            String sql = "SELECT * FROM mstable where m_pass=? ";
                            PreparedStatement pst = con.prepareStatement(sql);
                            pst.setString(1,password);
                            ResultSet rs = pst.executeQuery();
                            if(rs.next()) {
                                new welcomeMs();
                                dispose();
                            }
                            else { JOptionPane.showMessageDialog(null,"wrong id , Please try again ");
                                 } }
                        catch ( SQLException ex) { System.out.println(ex); }
                       } });
           panel.add(login);
        //back button :
        setVisible(true);

    }
    public String getuserName() {
        return this.user;
    }
}

i want to show the name in this class

// i extend this class to the last Class
try {
            // Class.forName("com.mysql.jdbc.Driver");
            String host = "jdbc:mysql://localhost:3306/mybase?serverTimezone=UTC";
            String uName = "root";
            String uPass = "dataroot";
            Connection con = DriverManager.getConnection(host, uName, uPass);
            String sql = "SELECT m_name FROM mstable where m_pass = 'getuserName()' ";
            PreparedStatement pst = con.prepareStatement(sql);
            //pst.setString(1, getuserName());
            ResultSet rs = pst.executeQuery();
            rs.next();
                JLabel label = new JLabel();
                label.setText(rs.getString(1) + " welcome ");
                label.setBounds(402, -295, size.width, size.height);
                panel.add(label);
        } catch (SQLException ex) {
            JOptionPane.showMessageDialog(null,ex);
        }
f.setVisible(true);

When I try to log in, this message appears " lllegal operation on empty result set " or when i remove the // " Parameter index is out of range (1> number of parameters, which is 0)." i think error at

 pst.setString(1, getuserName());

//or

  label.setText(rs.getString(1) + " welcome ");

Answer 1

From your error message it is clear that your query is returning resultset that contains 0 rows and 1 column. I assume that you want to compare column m_pass to returned value of JAVA function getuserName() (Or you might want to compare with user password).

You can try following:

1. Update your query code to this:

String sql = "SELECT m_name FROM mstable where m_pass = ?";
PreparedStatement pst = con.prepareStatement(sql);
pst.setString(1, getuserName()); //Or any string that you want to compare

2. You should always check if record exists in result set before consuming it. you can do this by

if (rs.next()) {
   // record found 
}
else {
  // record not found
}

3. Try executing same query on your database directly using SQL Sever Management Studio or any equivalent IDE and see if it returns any rows.

Read more about PreparedStatement and JDBC ResultSet. Hope it helps!