【Java】通過 JDBC 連接 MySQL 數據庫並使用預處理語句對數據庫內容查詢和更新

作業要求

（1）先用MySQL建立一個數據庫Users，然後在數據庫裏建立一個表。表中每條記錄，存儲了用戶名、密碼、上次登錄時間。請你在表中輸入3條記錄。請截圖。
（2）編寫一個帶窗體的程序，用戶輸入用戶名和密碼，程序與數據庫中的信息比對，用消息對話框輸出結果：若正確，輸出上次登錄時間；若錯誤，提示用戶重新輸入。

步驟與源碼

1、先在MySQL中按作業要求（1）創建實驗數據。

create database Users;
use Users;
create table LoginTable (Login varchar(32) primary key, Password varchar(32), LastLogin datetime);
insert into LoginTable values("Hank Pym", "fheh0r23r3uwdj0i", "2020-06-04 10:46:32");
insert into LoginTable values("Scott Lang", "ur983rjwfjd230du20riu2", "2020-06-04 10:48:58");
insert into LoginTable values("Hope Pym", "r8432my88ryn03r34t9r2d", "2020-06-04 10:50:27");

2、在MySQL中修改登錄密碼。

3、執行如下代碼，將數據庫的三個用戶各成功登錄一次。

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class Main {
	public static void main(String[] args) throws SQLException { G.ConnectToMySQL(); G.CreateUI(); }
}

class G {
	static JTextField textLogin; static JPasswordField textPassword; static Connection c;
	static void CreateUI() throws SQLException {
		JFrame frame = new JFrame("Login");
		Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
		frame.setBounds(screen.width / 2 - 160, screen.height / 2 - 90, 320, 180); frame.setResizable(false);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.addWindowListener(new WndClosingDetecter());
		JPanel panel = new JPanel(new FlowLayout());
		frame.setContentPane(panel);
		JLabel InputHints = new JLabel("Enter your login and password:");
		textLogin = new JTextField(27); textPassword = new JPasswordField(27);
		JButton buttonLogin = new JButton("Login");
		buttonLogin.addActionListener(new LoginQuestDetecter());
		panel.add(InputHints); panel.add(textLogin); panel.add(textPassword); panel.add(buttonLogin);
		frame.setVisible(true);
	}
	static void ConnectToMySQL() throws SQLException {
		String url = "jdbc:mysql://localhost:3306/Users?useSSL=true&serverTimezone=GMT%2B8", login = "Andy", password = "        ";
		c = DriverManager.getConnection(url, login, password);
	}
}

class LoginQuestDetecter implements ActionListener {
	PreparedStatement s, t; String Login, Password, LastLogin; ResultSet r; DateTimeFormatter f; LocalDateTime d;
	LoginQuestDetecter() throws SQLException {
		f = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
		s = G.c.prepareStatement("SELECT Password, LastLogin from LoginTable where Login = ?");
		t = G.c.prepareStatement("update LoginTable set LastLogin = ? where Login = ?");
	}
	public void actionPerformed(ActionEvent e) {
		try {
			Login = G.textLogin.getText(); s.setString(1, Login); r = s.executeQuery();
			if (!r.isBeforeFirst()) { JOptionPane.showMessageDialog(null, "該用戶不存在。"); return; }
			r.next(); Password = r.getString(1);
			if (Password.equals(String.valueOf(G.textPassword.getPassword()))) {
				LastLogin = r.getString(2); d = LocalDateTime.now();
				JOptionPane.showMessageDialog(null, "登錄成功。\n上次登錄時間：" + LocalDateTime.parse(LastLogin, f) + "\n該記錄將修改爲本次登錄時間：" + d.format(f) + "。");
				t.setString(1, d.format(f)); t.setString(2, Login); t.executeUpdate();
			}
			else { JOptionPane.showMessageDialog(null, "用戶名或密碼錯誤。", "登錄失敗", JOptionPane.WARNING_MESSAGE); }
		}
		catch (SQLException e1) { e1.printStackTrace(); }
	}
}

class WndClosingDetecter implements WindowListener {
	public void windowClosing(WindowEvent e) {
		try { G.c.close(); }
		catch (SQLException e1) { e1.printStackTrace(); }
	}
	public void windowOpened(WindowEvent e) {}
	public void windowClosed(WindowEvent e) {}
	public void windowIconified(WindowEvent e) {}
	public void windowDeiconified(WindowEvent e) {}
	public void windowActivated(WindowEvent e) {}
	public void windowDeactivated(WindowEvent e) {}
}

運行截圖

登錄前：

登錄過程：