@Entity
@Table(name = "t_user")
public class UserDO {
    private Long id;
    private String username;
    private String password; // 敏感字段
    private String email;
    private String phone;
    private LocalDateTime createTime;
    private LocalDateTime updateTime;
    private Integer status; // 0-注銷 1-正常 2-凍結
}

@Data
public class UserOrderDTO {
    // 用戶基本信息
    private Long userId;
    private String username;
    private String email; // 可能包含敏感信息
    
    // 訂單列表（跨聚合數據）
    private List<OrderDTO> orders;
    
    // 統(tǒng)計信息
    private Integer totalOrderCount;
    private BigDecimal totalAmount;
    
    // 原始數據類型
    private LocalDateTime userCreateTime;
}

@Service
public class UserOrderService {
    public UserOrderDTO getUserWithOrders(Long userId) {
        UserDO user = userDao.findById(userId);
        List<OrderDO> orders = orderDao.findByUserId(userId);
        
        // 轉換并聚合數據
        UserOrderDTO dto = new UserOrderDTO();
        dto.setUserId(user.getId());
        dto.setUsername(user.getUsername());
        dto.setEmail(user.getEmail()); // 直接暴露原始郵箱
        dto.setOrders(convertOrders(orders));
        dto.setTotalOrderCount(orders.size());
        return dto;
    }
}

@Data
public class UserOrderVO {
    // 前端展示字段（脫敏）
    private Long userId;
    private String username;
    private String maskedEmail; // 脫敏：a****@gmail.com
    
    // 訂單數據（按需展示）
    private List<OrderVO> orders;
    
    // 格式化后的數據
    private String formattedTotalAmount; // "￥9,999.00"
    private String userCreateTimeDesc; // "2025-01-15 12:00"
    
    // 前端狀態(tài)（計算得出）
    private String userStatusText; // "正常" 而非 1
    
    // 不包含：password, phone, raw status
}

@RestController
@RequestMapping("/api/users")
public class UserOrderController {
    
    @Resource
    private UserOrderService userOrderService;
    
    @GetMapping("/{userId}/orders")
    public ResultVO<UserOrderVO> getUserOrders(@PathVariable Long userId) {
        UserOrderDTO dto = userOrderService.getUserWithOrders(userId);
        
        // DTO → VO 轉換（關鍵一步！）
        UserOrderVO vo = new UserOrderVO();
        vo.setUserId(dto.getUserId());
        vo.setUsername(dto.getUsername());
        
        // 1. 脫敏處理
        vo.setMaskedEmail(maskEmail(dto.getEmail())); // a****@gmail.com
        
        // 2. 數據格式化
        vo.setFormattedTotalAmount(formatCurrency(dto.getTotalAmount()));
        vo.setUserCreateTimeDesc(formatDateTime(dto.getUserCreateTime()));
        
        // 3. 狀態(tài)轉換
        vo.setUserStatusText(convertStatusToText(user.getStatus())); // "正常"
        
        // 4. 按需過濾字段
        vo.setOrders(convertToOrderVO(dto.getOrders()));
        
        return ResultVO.success(vo);
    }
}

// 錯誤：Controller 直接返回 DTO，暴露敏感信息
@RestController
public class UserController {
    public UserOrderDTO getUserOrders(Long userId) {
        return userOrderService.getUserWithOrders(userId); // ? 暴露了 password 等字段
    }
}

// 錯誤：VO 包含計算邏輯
@Data
public class UserOrderVO {
    private BigDecimal orderAmount;
    private BigDecimal discount;
    
    // ? VO 只應承載數據，不應有業(yè)務方法
    public BigDecimal getPayAmount() {
        return orderAmount.subtract(discount); // 計算應在后端完成
    }
}

// 錯誤：為每個方法都創(chuàng)建 DTO
public class UserOrderService {
    public UserOrderDTO1 method1() { ... }
    public UserOrderDTO2 method2() { ... }
    public UserOrderDTO3 method3() { ... } // 維護噩夢
}

// 分層轉換
DAO層 → Service層 → Controller層 → 前端
  DO   →   DTO    →    VO      → JSON

// DTO 命名：業(yè)務 + DTO
UserDTO, OrderDTO, UserOrderDTO
 
// VO 命名：頁面/組件 + VO
OrderListVO, OrderDetailVO, UserProfileVO

@Component
public class UserConverter {
    
    // DO → DTO
    public UserDTO toDTO(UserDO userDO) {
        UserDTO dto = new UserDTO();
        BeanUtils.copyProperties(userDO, dto);
        return dto;
    }
    
    // DTO → VO（關鍵：脫敏+格式化）
    public UserVO toVO(UserDTO userDTO) {
        UserVO vo = new UserVO();
        vo.setUserId(userDTO.getUserId());
        vo.setUsername(userDTO.getUsername());
        vo.setMaskedEmail(this.maskEmail(userDTO.getEmail()));
        vo.setStatusText(this.convertStatus(userDTO.getStatus()));
        return vo;
    }
    
    private String maskEmail(String email) {
        // 脫敏邏輯
        return email.replaceAll("(?<=.).(?=.*@)", "*");
    }
}

@Data
public class ResultVO<T> {
    private int code;      // 狀態(tài)碼
    private String message; // 提示信息
    private T data;        // 實際數據（VO/DTO）
    
    public static <T> ResultVO<T> success(T data) {
        ResultVO<T> result = new ResultVO<>();
        result.setCode(200);
        result.setMessage("success");
        result.setData(data);
        return result;
    }
}