用户登录和注册系统的代码，将用户名、密码和上次登录时间存在MySQL数据库中，构建Users类，用于存放用户对象；创建Utils类，用于提供数据库连接和关闭方法；创建UsersDao类，用于提供数据库接口。

好的，以下是一个简单的用户登录和注册系统的代码示例，包括将用户名、密码和上次登录时间存在MySQL数据库中，构建Users类，用于存放用户对象；创建Utils类，用于提供数据库连接和关闭方法；创建UsersDao类，用于提供数据库接口。请注意，这只是一个简单的示例，您需要根据自己的实际需求进行调整和完善。

1. Users类

public class Users {
    private int id;
    private String username;
    private String password;
    private String lastLoginTime;

    // 构造方法
    public Users(int id, String username, String password, String lastLoginTime) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.lastLoginTime = lastLoginTime;
    }

    // getter 和 setter 方法
    // ...
}

2. Utils类

public class Utils {
    private static final String driver = "com.mysql.jdbc.Driver";
    private static final String url = "jdbc:mysql://localhost:3306/test";
    private static final String username = "root";
    private static final String password = "123456";

    // 获取数据库连接
    public static Connection getConnection() {
        Connection conn = null;
        try {
            Class.forName(driver);
            conn = DriverManager.getConnection(url, username, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return conn;
    }

    // 关闭数据库连接
    public static void closeConnection(Connection conn) {
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    // 关闭Statement
    public static void closeStatement(Statement stmt) {
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    // 关闭ResultSet
    public static void closeResultSet(ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

3. UsersDao类

public class UsersDao {
    // 添加用户
    public static boolean addUser(Users user) {
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            conn = Utils.getConnection();
            String sql = "INSERT INTO users (username, password, last_login_time) VALUES (?, ?, ?)";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, user.getUsername());
            pstmt.setString(2, user.getPassword());
            pstmt.setString(3, user.getLastLoginTime());
            int count = pstmt.executeUpdate();
            if (count > 0) {
                return true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            Utils.closeStatement(pstmt);
            Utils.closeConnection(conn);
        }
        return false;
    }

    // 根据用户名查询用户
    public static Users getUserByUsername(String username) {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            conn = Utils.getConnection();
            String sql = "SELECT * FROM users WHERE username=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, username);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                int id = rs.getInt("id");
                String password = rs.getString("password");
                String lastLoginTime = rs.getString("last_login_time");
                Users user = new Users(id, username, password, lastLoginTime);
                return user;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            Utils.closeResultSet(rs);
            Utils.closeStatement(pstmt);
            Utils.closeConnection(conn);
        }
        return null;
    }

    // 更新用户的上次登录时间
    public static boolean updateLastLoginTime(Users user) {
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            conn = Utils.getConnection();
            String sql = "UPDATE users SET last_login_time=? WHERE id=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, user.getLastLoginTime());
            pstmt.setInt(2, user.getId());
            int count = pstmt.executeUpdate();
            if (count > 0) {
                return true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            Utils.closeStatement(pstmt);
            Utils.closeConnection(conn);
        }
        return false;
    }
}

以上代码示例仅供参考，具体实现可以根据您的需求进行调整。希望能对您有所帮助！