DTO、VO、POJO與實體類使用方案（結合Mapper.xml）

結合MyBatis的Mapper.xml文件，展示完整的層級數據流轉和數據庫操作。

1. 實體類優化（Entity）

// User.java
@Data
@NoArgsConstructor
@AllArgsConstructor
@TableName("sys_user")
public class User {@TableId(type = IdType.AUTO)private Long userId;@NotBlankprivate String username;@NotBlankprivate String password;private String email;private String phone;private Date createTime;// 非數據庫字段，用于關聯查詢@TableField(exist = false)private List<Role> roles;
}// Role.java
@Data
@TableName("sys_role")
public class Role {@TableId(type = IdType.AUTO)private Long roleId;private String roleName;private String roleDesc;
}

2. Mapper接口與XML配置

UserMapper.java

@Mapper
public interface UserMapper {// 插入用戶并返回主鍵int insertUser(User user);// 根據ID查詢用戶（包含角色信息）User selectUserWithRoles(@Param("userId") Long userId);// 分頁查詢用戶List<User> selectUserList(UserQueryDTO queryDTO);// 批量插入用戶角色關系int batchInsertUserRoles(@Param("list") List<UserRole> userRoles);
}

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.example.mapper.UserMapper"><!-- 基本結果映射 --><resultMap id="BaseUserMap" type="com.example.entity.User"><id column="user_id" property="userId"/><result column="username" property="username"/><result column="password" property="password"/><result column="email" property="email"/><result column="phone" property="phone"/><result column="create_time" property="createTime"/></resultMap><!-- 包含角色信息的用戶映射 --><resultMap id="UserWithRolesMap" type="com.example.entity.User" extends="BaseUserMap"><collection property="roles" ofType="com.example.entity.Role"><id column="role_id" property="roleId"/><result column="role_name" property="roleName"/><result column="role_desc" property="roleDesc"/></collection></resultMap><!-- 插入用戶 --><insert id="insertUser" useGeneratedKeys="true" keyProperty="userId">INSERT INTO sys_user (username, password, email, phone)VALUES (#{username}, #{password}, #{email}, #{phone})</insert><!-- 查詢用戶及其角色 --><select id="selectUserWithRoles" resultMap="UserWithRolesMap">SELECT u.*, r.role_id, r.role_name, r.role_descFROM sys_user uLEFT JOIN sys_user_role ur ON u.user_id = ur.user_idLEFT JOIN sys_role r ON ur.role_id = r.role_idWHERE u.user_id = #{userId}</select><!-- 動態查詢用戶列表 --><select id="selectUserList" resultMap="BaseUserMap">SELECT * FROM sys_user<where><if test="username != null and username != ''">AND username LIKE CONCAT('%', #{username}, '%')</if><if test="email != null and email != ''">AND email = #{email}</if><if test="phone != null and phone != ''">AND phone = #{phone}</if><if test="createTimeStart != null">AND create_time >= #{createTimeStart}</if><if test="createTimeEnd != null">AND create_time &lt;= #{createTimeEnd}</if></where>ORDER BY create_time DESC</select><!-- 批量插入用戶角色關系 --><insert id="batchInsertUserRoles">INSERT INTO sys_user_role (user_id, role_id)VALUES<foreach collection="list" item="item" separator=",">(#{item.userId}, #{item.roleId})</foreach></insert>
</mapper>

3. 服務層優化實現

@Service
@RequiredArgsConstructor
public class UserServiceImpl implements UserService {private final UserMapper userMapper;private final RoleMapper roleMapper;private final PasswordEncoder passwordEncoder;@Override@Transactionalpublic UserVO createUser(UserDTO userDTO) {// DTO轉EntityUser user = new User();BeanUtils.copyProperties(userDTO, user);// 密碼加密user.setPassword(passwordEncoder.encode(userDTO.getPassword()));// 保存用戶userMapper.insertUser(user);// 保存用戶角色關系if (!CollectionUtils.isEmpty(userDTO.getRoleIds())) {List<UserRole> userRoles = userDTO.getRoleIds().stream().map(roleId -> new UserRole(user.getUserId(), roleId)).collect(Collectors.toList());userMapper.batchInsertUserRoles(userRoles);}// 返回完整的用戶信息return getUserVO(user.getUserId());}@Overridepublic PageVO<UserVO> getUsers(UserQueryDTO queryDTO) {// 設置分頁參數PageHelper.startPage(queryDTO.getPageNum(), queryDTO.getPageSize());// 查詢用戶列表List<User> users = userMapper.selectUserList(queryDTO);PageInfo<User> pageInfo = new PageInfo<>(users);// 轉換為VO列表List<UserVO> userVOs = users.stream().map(user -> UserVO.fromEntity(user, getRolesByUserId(user.getUserId()))).collect(Collectors.toList());// 構建分頁VOreturn new PageVO<>(pageInfo.getTotal(),pageInfo.getPageNum(),pageInfo.getPageSize(),userVOs);}@Overridepublic UserVO getUserVO(Long userId) {User user = userMapper.selectUserWithRoles(userId);return UserVO.fromEntity(user, user.getRoles());}private List<Role> getRolesByUserId(Long userId) {return roleMapper.selectByUserId(userId);}
}

4. DTO/VO優化設計

UserDTO.java

@Data
public class UserDTO {@NotBlank(message = "用戶名不能為空")@Size(min = 4, max = 20)private String username;@NotBlank(message = "密碼不能為空")@Size(min = 6, max = 20)@Pattern(regexp = "^(?=.*[A-Za-z])(?=.*\\d).*$", message = "密碼必須包含字母和數字")private String password;@Emailprivate String email;@Pattern(regexp = "^1[3-9]\\d{9}$")private String phone;@NotEmpty(message = "至少分配一個角色")private List<Long> roleIds;// 自定義轉換方法public User toEntity() {User user = new User();BeanUtils.copyProperties(this, user);return user;}
}

UserVO.java

@Data
@Accessors(chain = true)
public class UserVO {private Long userId;private String username;private String email;private String phone;@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")private Date createTime;private List<RoleVO> roles;// 靜態工廠方法public static UserVO fromEntity(User user, List<Role> roles) {return new UserVO().setUserId(user.getUserId()).setUsername(user.getUsername()).setEmail(user.getEmail()).setPhone(user.getPhone()).setCreateTime(user.getCreateTime()).setRoles(roles.stream().map(RoleVO::fromEntity).collect(Collectors.toList()));}
}

PageVO.java (通用分頁VO)

@Data
@AllArgsConstructor
public class PageVO<T> {private Long total;private Integer pageNum;private Integer pageSize;private List<T> list;// 計算總頁數public Integer getPages() {if (pageSize == 0) return 0;return (int) Math.ceil((double) total / pageSize);}
}

5. 控制器層優化

@RestController
@RequestMapping("/api/users")
@RequiredArgsConstructor
public class UserController {private final UserService userService;@PostMappingpublic ResponseEntity<Result<UserVO>> createUser(@Valid @RequestBody UserDTO userDTO) {UserVO userVO = userService.createUser(userDTO);return ResponseEntity.ok(Result.success(userVO));}@GetMappingpublic ResponseEntity<Result<PageVO<UserVO>>> getUsers(@Valid UserQueryDTO queryDTO) {PageVO<UserVO> page = userService.getUsers(queryDTO);return ResponseEntity.ok(Result.success(page));}@GetMapping("/{userId}")public ResponseEntity<Result<UserVO>> getUser(@PathVariable Long userId) {UserVO userVO = userService.getUserVO(userId);return ResponseEntity.ok(Result.success(userVO));}
}// 通用返回結果
@Data
@AllArgsConstructor
class Result<T> {private int code;private String message;private T data;public static <T> Result<T> success(T data) {return new Result<>(200, "success", data);}
}

6. 優化后的數據流轉流程

前端請求 → Controller（接收DTO并校驗）
Controller → Service（傳遞DTO）
Service：
- 將DTO轉換為Entity
- 調用Mapper進行數據庫操作
- 將查詢結果Entity轉換為VO
Service → Controller（返回VO）
Controller → 前端（返回VO數據）

7. 關鍵優化點

Mapper.xml優化：
- 使用resultMap實現復雜結果映射
- 動態SQL處理各種查詢條件
- 批量操作提高性能
對象轉換優化：
- 在DTO/VO中定義轉換方法
- 使用鏈式調用簡化代碼
- 靜態工廠方法提高可讀性
分頁處理：
- 使用PageHelper實現物理分頁
- 統一分頁返回結構
驗證增強：
- 在DTO中使用更精細的驗證注解
- 密碼復雜度驗證
性能優化：
- 關聯查詢減少數據庫訪問次數
- 批量插入提高效率

這種結構清晰地區分了各層職責，使代碼更易維護和擴展，同時保證了良好的性能。

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