如何在java类方法中连接到数据库sql，并在另一个类中调用它？

Question

我试图创建一个桌面应用程序使用corba和java swing图形界面。

如您所知，在CORBA中，我们必须使主要的方法像：连接到数据库，计算······因此，我在服务器类中创建了一个用于连接数据库的方法。

java类方法如下所示：

public  void connect_db(){
    // TODO Auto-generated method stub

    JTextField txtUsername = FrameLogin.txtUsername;
     JPasswordField pwd= FrameLogin.pwd;
    JLabel lblLoginMessage= FrameLogin.lblLoginMessage;
    
    try {
        Class.forName("com.mysql.cj.jdbc.Driver");
        Connection conn =(Connection)DriverManager.getConnection("jdbc:mysql://localhost:3306/utilisateurs","root", "Mrayhana123");
        Statement stm = conn.createStatement();
        String sql="select * from etudiant where username='"+txtUsername+"' and pwd='"+pwd+"'";
        ResultSet result = stm.executeQuery(sql);
        if(result.next()){
            lblLoginMessage.setText("you are connected");
            lblLoginMessage.setForeground(Color.GREEN);
        
        
        }
        else {
            lblLoginMessage.setText("Incorrect username or password!");
            lblLoginMessage.setForeground(Color.RED);
        }

    } catch(Exception e){
        //System.out.println("not connected to database");
        e.printStackTrace();
}
}

public static JTextField txtUsername;
   public static JPasswordField pwd;
   public static JLabel lblLoginMessage = new JLabel("");

 pnlBtnlogin.addMouseListener(new MouseAdapter() {
            @Override
            
                  String username = txtUsername.getText();
                    String pwd= pwd.getText();
                    
                    try {
                        
                        SraCorbaImpl sci = new SraCorbaImpl();
                        sci.connect_db();
                        
                    } catch(Exception e1){
                        //System.out.println("not connected to database");
                        e1.printStackTrace();               
                        }
                    

Answer 1

根据您的评论，我知道您成功连接到数据库，但查询没有返回任何行。

如果问题中的代码是实际代码，那么将JTextField传递给[SQL]查询，而不是JTextField的文本。密码也是如此。您传递的是JPasswordField，而不是实际的密码。

尝试下面的代码。

public  void connect_db(){
    JTextField txtUsername = FrameLogin.txtUsername;
    JPasswordField pwd= FrameLogin.pwd;
    JLabel lblLoginMessage= FrameLogin.lblLoginMessage;
    try {
//        Class.forName("com.mysql.cj.jdbc.Driver"); <- not required
        Connection conn =(Connection)DriverManager.getConnection("jdbc:mysql://localhost:3306/utilisateurs","root", "Mrayhana123");
        Statement stm = conn.createStatement();
        String sql="select * from etudiant where username='"+txtUsername.getText()+"' and pwd='"+pwd.getText()+"'";  // Change here.
        ResultSet result = stm.executeQuery(sql);
        if(result.next()){
            lblLoginMessage.setText("you are connected");
            lblLoginMessage.setForeground(Color.GREEN);
        }
        else {
            lblLoginMessage.setText("Incorrect username or password!");
            lblLoginMessage.setForeground(Color.RED);
        }
    } catch(Exception e){
        //System.out.println("not connected to database");
        e.printStackTrace();
}

String sql="select * from etudiant where username=? and pwd=?";
PreparedStatement ps = conn.prepareStatement(sql);
ps.setString(1, txtUsername.getText());
ps.setString(2, pwd.getText());