java - 如何在 Java-mysql 中验证用户名和密码？

Question

如何以最正确的方式验证用户输入数据库的用户名和密码？

In c++, we used to verify by using if-else:
    if((user == "username")&&(pass == "password")){
             cout<<"You are now logon!";
    }

在 java-mysql 中我不确定我是否在正确的轨道上:

登录按钮

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
        // TODO add your handling code here:

        user = jTextField1.getText();
        pass = jPasswordField1.getPassword();
        login();
}

方法/函数

private void login() {

        try {
                if (user != null) {
                sql = "Select * from users_table Where username='" + user + "'";
                rs = stmt.executeQuery(sql);

                rs.next();
                username = rs.getString("username");
                password = rs.getString("password");

            }
        } 
    catch (SQLException err) {
            JOptionPane.showMessageDialog(this, err.getMessage());
        }

}

如果用户输入的用户名和密码与数据库中的匹配，那么他将被引导到一个新的 jFrame else将弹出消息对话框，提示用户名或密码无效。有人可以帮我处理我的代码吗，我不知道如何在 mysql 中使用 if-else 语句；

谢谢! :)

Answer 1

执行下面的代码:

private void login() {
    try {
        if (user != null && pass != null) {
            String sql = "Select * from users_table Where username='" + user + "' and password='" + pass + "'";
            rs = stmt.executeQuery(sql);
            if (rs.next()) {
                //in this case enter when at least one result comes it means user is valid
            } else {
                //in this case enter when  result size is zero  it means user is invalid
            }
        }

        // You can also validate user by result size if its comes zero user is invalid else user is valid

    } catch (SQLException err) {
        JOptionPane.showMessageDialog(this, err.getMessage());
    }

}