public class DataMaskingUtil {

    /**
     * 脫敏處理：將字符串的中間部分用指定字符替換。
     *
     * @param str         待脫敏的字符串
     * @param start       開始保留多少位
     * @param end         末尾保留多少位
     * @param maskChar    替換的字符
     * @return            脫敏處理后的字符串
     */
    public static String mask(String str, int start, int end, char maskChar) {
        if (str == null || str.length() <= start + end) {
            return str;
        }

        StringBuilder maskedString = new StringBuilder();
        for (int i = 0; i < str.length(); i++) {
            if (i < start || i >= str.length() - end) {
                maskedString.append(str.charAt(i));
            } else {
                maskedString.append(maskChar);
            }
        }
        return maskedString.toString();
    }

    /**
     * 對手機號進行脫敏處理
     *
     * @param phoneNumber 原始手機號
     * @return            脫敏后的手機號
     */
    public static String maskPhoneNumber(String phoneNumber) {
        return mask(phoneNumber, 3, 4, '*');
    }

    /**
     * 對身份證號進行脫敏處理
     *
     * @param idNumber 原始身份證號
     * @return         脫敏后的身份證號
     */
    public static String maskIDNumber(String idNumber) {
        return mask(idNumber, 3, 4, '*');
    }

    /**
     * 對電子郵箱進行脫敏處理
     *
     * @param email 原始電子郵箱
     * @return      脫敏后的電子郵箱
     */
    public static String maskEmail(String email) {
        if (email == null || !email.contains("@")) {
            return email;
        }

        String[] parts = email.split("@");
        String localPart = parts[0];
        String domainPart = parts[1];

        String maskedLocalPart = localPart.length() <= 2 ? localPart : mask(localPart, 1, 1, '*');
        return maskedLocalPart + "@" + domainPart;
    }

    /**
     * 對信用卡號進行脫敏處理
     *
     * @param creditCardNumber 原始信用卡號
     * @return                 脫敏后的信用卡號
     */
    public static String maskCreditCardNumber(String creditCardNumber) {
        return mask(creditCardNumber, 4, 4, '*');
    }

    public static void main(String[] args) {
        // 測試脫敏處理
        System.out.println("Phone Number: " + maskPhoneNumber("13812345678"));
        System.out.println("ID Number: " + maskIDNumber("123456789012345678"));
        System.out.println("Email: " + maskEmail("example@example.com"));
        System.out.println("Credit Card Number: " + maskCreditCardNumber("1234123412341234"));
    }
}

public class User {
    private int id;
    private String name;
    private String phoneNumber;
    private String idNumber;
    private String email;
    private String creditCardNumber;

    // Getters and setters
    // ...
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class UserService {
    private static final String URL = "jdbc:mysql://localhost:3306/sensitive_data_db";
    private static final String USER = "root";
    private static final String PASSWORD = "password";

    public User getUserById(int userId) throws Exception {
        User user = null;
        try (Connection conn = DriverManager.getConnection(URL, USER, PASSWORD)) {
            String sql = "SELECT * FROM users WHERE id = ?";
            try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
                pstmt.setInt(1, userId);
                ResultSet rs = pstmt.executeQuery();
                if (rs.next()) {
                    user = new User();
                    user.setId(rs.getInt("id"));
                    user.setName(rs.getString("name"));
                    user.setPhoneNumber(DataMaskingUtil.maskPhoneNumber(rs.getString("phone_number")));
                    user.setIdNumber(DataMaskingUtil.maskIDNumber(rs.getString("id_number")));
                    user.setEmail(DataMaskingUtil.maskEmail(rs.getString("email")));
                    user.setCreditCardNumber(DataMaskingUtil.maskCreditCardNumber(rs.getString("credit_card_number")));
                }
            }
        }
        return user;
    }

    public static void main(String[] args) throws Exception {
        UserService userService = new UserService();
        User user = userService.getUserById(1);
        if (user != null) {
            System.out.println("User ID: " + user.getId());
            System.out.println("Name: " + user.getName());
            System.out.println("Phone Number: " + user.getPhoneNumber());
            System.out.println("ID Number: " + user.getIdNumber());
            System.out.println("Email: " + user.getEmail());
            System.out.println("Credit Card Number: " + user.getCreditCardNumber());
        }
    }
}