我试图用 MySql 数据填充 JTable。事情是当我运行登录类时，我收到消息“java.SQLException：没有为参数 2 指定值”，当我运行 JTable 类时，我不断收到 java.lang.NullPointerException 错误。我有三个类： 1-连接到数据库：
import java.sql.Connection;
import java.sql.DriverManager;
import javax.swing.JOptionPane;
public class javaconnect {
Connection conn = null;
public static Connection ConnecrDB() {
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/mydb",
"root", "root");
JOptionPane.showMessageDialog(null, "Connected");
return con;
} catch (Exception e) {
System.out.println("ERROR: " + e.getMessage());
}
return null;
}
}
第二类是登录框架：
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JLabel;
import java.awt.*;
import javax.swing.JOptionPane;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
public class JFrameLogIn extends JFrame {
Connection conn =null;
ResultSet rs = null;
PreparedStatement pst = null;
private JPanel contentPane;
private JPasswordField txt_Password;
private JTextField txt_Username;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
JFrameLogIn frame = new JFrameLogIn();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public JFrameLogIn() {
conn=javaconnect.ConnecrDB();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 375, 214);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
JLabel lblUsername = new JLabel("Username:");
lblUsername.setFont(new Font("Tahoma", Font.BOLD, 13));
lblUsername.setBounds(126, 45, 80, 14);
contentPane.add(lblUsername);
JLabel lblPassword = new JLabel("Password:");
lblPassword.setFont(new Font("Tahoma", Font.BOLD, 13));
lblPassword.setBounds(126, 82, 69, 14);
contentPane.add(lblPassword);
txt_Password = new JPasswordField();
txt_Password.setBounds(218, 82, 109, 20);
contentPane.add(txt_Password);
txt_Username = new JTextField();
txt_Username.setBounds(216, 43, 111, 20);
contentPane.add(txt_Username);
txt_Username.setColumns(10);
JButton cmd_Login = new JButton("Login");
cmd_Login.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
String sql = "Select * from clients where username=? and password=?";
try{
pst = conn.prepareStatement(sql);
pst.setString(1, txt_Username.getText());
pst.setString(1, txt_Password.getText());
rs = pst.executeQuery();
if(rs.next()){
JOptionPane.showMessageDialog(null, "Username and Password are correct");
}
else {
JOptionPane.showMessageDialog(null, "Username and Password are not correct");
}
}
catch(Exception e){
JOptionPane.showMessageDialog(null, e);
}
}
});
cmd_Login.setBounds(218, 125, 80, 23);
contentPane.add(cmd_Login);
}
}
最后一个是JTable
import java.awt.EventQueue;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
import java.sql.*;
import net.proteanit.sql.DbUtils;
public class JTable1 extends JFrame {
Connection conn = null;
ResultSet rs = null;
PreparedStatement pst = null;
private JPanel contentPane;
private JTable table_Admins;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
JTable1 frame = new JTable1();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public JTable1() {
conn = javaconnect.ConnecrDB();
UpdateTable ();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 450, 300);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
table_Admins = new JTable();
table_Admins.setBounds(30, 28, 378, 54);
contentPane.add(table_Admins);
}
private void UpdateTable () {
try {
String sql = "SELECT *FROM menu";
pst = conn.prepareStatement(sql);
rs = pst.executeQuery();
table_Admins.setModel(DbUtils.resultSetToTableModel(rs));
}
catch (Exception e){
JOptionPane.showMessageDialog(null, e);
}
}
}
我试图找出问题所在，但找不到解决方案。连接有效。非常感谢您在修复此错误方面的帮助。