写出java代码，查找键盘输入到JPasswordField的一串数字是否在所连接的数据库中，

好的，以下是一个简单的 Java 代码示例，可以实现您的要求：

import java.sql.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;

public class PasswordChecker extends JFrame implements ActionListener {
    private JLabel label;
    private JPasswordField passwordField;
    private JButton button;
    private Connection conn = null;
    private PreparedStatement ps = null;
    private ResultSet rs = null;

    public PasswordChecker() {
        super("Password Checker");

        label = new JLabel("Please enter your password:");
        passwordField = new JPasswordField(20);
        button = new JButton("Check");
        button.addActionListener(this);

        JPanel panel = new JPanel(new GridLayout(2, 1));
        panel.add(label);
        panel.add(passwordField);

        JPanel buttonPanel = new JPanel(new FlowLayout(FlowLayout.CENTER));
        buttonPanel.add(button);

        Container container = getContentPane();
        container.add(panel, BorderLayout.NORTH);
        container.add(buttonPanel, BorderLayout.SOUTH);

        pack();
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        String password = new String(passwordField.getPassword());

        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydatabase", "root", "password");

            String sql = "SELECT * FROM passwords WHERE password = ?";
            ps = conn.prepareStatement(sql);
            ps.setString(1, password);
            rs = ps.executeQuery();

            if (rs.next()) {
                JOptionPane.showMessageDialog(this, "Password is correct!");
            } else {
                JOptionPane.showMessageDialog(this, "Password is incorrect!");
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            try {
                if (rs != null) rs.close();
                if (ps != null) ps.close();
                if (conn != null) conn.close();
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        new PasswordChecker();
    }
}

请注意，这只是一个简单的示例，需要根据您的具体需求进行修改和优化。此外，为了使代码更加安全，建议使用加密算法对密码进行编码和解码。