如何使用 Java 在 MySQL 表中仅搜索一条特定记录

Question

我正在制作一个应用程序，我正在尝试使用存储在 MySQL 服务器中的数据登录用户。 我遇到的问题是，当我尝试使用正确的用户名和密码登录时，我的代码实际上是在检查“adminData”表中的每条记录，并向我显示每条记录的相应结果！ 我也附上我的代码，请看一下！ 所以我想问我怎么只能搜索一个特定的记录，它只会让我恢复那个特定的记录！ 请帮帮我.. :)

btnSubmit.addActionListener(new ActionListener()
{
    public void actionPerformed(ActionEvent e)
    {
        String query = "SELECT username, password FROM adminData";
        String username = null;
        String password = null;
        ;
        try
        {
            rs = st.executeQuery(query);
            String fieldWarning = "*all field are mandatory!";

            String enteredUsername = usernameField.getText();
            @SuppressWarnings("deprecation") String enteredPassword = passwordField.getText();

            usernameField.setCursor(null);
            fieldLabel.setText("");

            int userLen = enteredUsername.length();
            int passLen = enteredPassword.length();

            if (userLen != 0 && passLen != 0)
            {
                if (userLen <= 32 && passLen <= 32)
                {
                    while (rs.next())
                    {
                        username = rs.getString("username");
                        password = rs.getString("password");
                        if (enteredUsername.equals(username))
                        {
                            if (enteredPassword.contentEquals(password))
                            {
                                AdminDashboard frame = new AdminDashboard();
                                frame.setVisible(true);
                                frame.dispose();
                            }
                            else
                            {
                                JOptionPane.showMessageDialog(null, "Password Missmatch");
                            }

                        }
                        else
                        {
                            JOptionPane.showMessageDialog(null, "Invalid User");
                            passwordField.setText("");
                            usernameField.setText("");
                            usernameField.setCursor(null);

                        }
                    }
                }
                else
                {
                    JOptionPane.showMessageDialog(null,
                        "Please enter a valid username or password! \n(Note: Only 32 char MAX)");
                    passwordField.setText("");
                    usernameField.setText("");
                }
            }
            else
            {
                fieldLabel.setText(fieldWarning);
                usernameField.setCursor(null);
            }
        }
        catch (SQLException e1)
        {
            JOptionPane.showMessageDialog(null, "Database Error: " + e1);
        }
    }
});

Answer 1

这是因为您的查询会返回整个表格。如果您有用户名，您可以简单地调整查询以仅返回包含该特定用户详细信息的行，而不是所有用户。 因此，只需在查询之前分配输入的用户名，并将用户名条件添加到您的 sql 查询中。

btnSubmit.addActionListener(new ActionListener()
    {
public void actionPerformed(ActionEvent e)
{
    String enteredUsername = usernameField.getText();
    String query = "SELECT username, password FROM adminData WHERE username='"+enteredUsername+"'";
    String username = null;
    String password = null;
    ;
    try
    {
        rs = st.executeQuery(query);
        String fieldWarning = "*all field are mandatory!";

        @SuppressWarnings("deprecation") String enteredPassword = passwordField.getText();

        usernameField.setCursor(null);
        fieldLabel.setText("");

        int userLen = enteredUsername.length();
        int passLen = enteredPassword.length();

        if (userLen != 0 && passLen != 0)
        {
            if (userLen <= 32 && passLen <= 32)
            {
                while (rs.next())
                {
                    username = rs.getString("username");
                    password = rs.getString("password");
                    if (enteredUsername.equals(username))
                    {
                        if (enteredPassword.contentEquals(password))
                        {
                            AdminDashboard frame = new AdminDashboard();
                            frame.setVisible(true);
                            frame.dispose();
                        }
                        else
                        {
                            JOptionPane.showMessageDialog(null, "Password Missmatch");
                        }

                    }
                    else
                    {
                        JOptionPane.showMessageDialog(null, "Invalid User");
                        passwordField.setText("");
                        usernameField.setText("");
                        usernameField.setCursor(null);

                    }
                }
            }
            else
            {
                JOptionPane.showMessageDialog(null,
                    "Please enter a valid username or password! \n(Note: Only 32 char MAX)");
                passwordField.setText("");
                usernameField.setText("");
            }
        }
        else
        {
            fieldLabel.setText(fieldWarning);
            usernameField.setCursor(null);
        }
    }
    catch (SQLException e1)
    {
        JOptionPane.showMessageDialog(null, "Database Error: " + e1);
    }
}
    });

现在，只要您的用户名是唯一的，它就会始终返回一条记录。