1：项目结构图

2：TUser.java

/**
 * @Author ZGM
 * @DateTime 2021/12/31
 * @description
 */
@Data
@Entity
@Table(name = "t_user")
@AllArgsConstructor
@NoArgsConstructor
@DynamicUpdate
@DynamicInsert
public class TUser {
    @Id
    @JsonSerialize(using = ToStringSerializer.class)
    private Long id;

    @Column(name = "user_name")
    private String userName;

    @Column(name = "pass_word")
    @JsonIgnore
    private String passWord;

    @Column(name = "nick_name")
    private String nickName;

    @Column(name = "sex")
    private String sex;

    @Column(name = "age")
    private Integer age;

    @Column(name = "status")
    private String status;

    @Column(name = "create_time")
    private Date createTime;

    @Column(name = "update_time")
    private Date updateTime;

    @PreUpdate
    protected void onUpdate() {
        updateTime = new Date();
    }

    @PrePersist
    protected void onCreate() {
        createTime = new Date();
        updateTime = new Date();
    }

    @JsonIgnore
    @Version
    @Column(name = "version")
    private int version;

    @Column(name = "role")
    private String role;
}

3:UserInfo.java

@Data
@Entity
@Table(name = "user_info")
public class UserInfo {

	@Id
	@JsonSerialize(using = ToStringSerializer.class)
	private Long id;

	private String profession;

	private String grade;

	private String dormitory;

}

4:实体类对应的数据库接口
TUserRepository

@Repository
public interface TUserRepository extends JpaRepository<TUser, Long>, JpaSpecificationExecutor<TUser> {
}

UserInfoRepository

@Repository
public interface UserInfoRepository extends JpaRepository<UserInfo, Long>, JpaSpecificationExecutor<UserInfo> {
@Query(value = "select new com.example.vo.UserVo(info.id, user.userName, info.profession, info.grade) from UserInfo info left join TUser user on info.id = user.id" +
        " where ( info.profession = ?1 or ?1 is null) " +
        " and ( info.grade = ?2 or ?2 is null)")
Page<UserVo> allUser(String profession, String grade, Pageable pageable);
}

5: UserVo.java

@Data
@AllArgsConstructor
public class UserVo {
    Long id;
    String userName;
    String profession;
    String grade;
}

6: UserService.java

@Service
@RequiredArgsConstructor
@RefreshScope
public class UserService extends KeyGenService {
    private final UserInfoRepository infoRepository;
   
    public Page<UserVo> list(UserQueryVo vo){
        Pageable pageable = PageRequest.of(vo.getPage(),vo.getSize());
        return infoRepository.allUser(vo.getProfession(),vo.getGrade(), pageable);
    }

}

7: UserController.java

@RestController
@RequestMapping("/v1/user")
@RequiredArgsConstructor
public class UserController {
    private final UserService userService;

    @PostMapping("/list")
    public Page<UserVo> list(@RequestBody UserQueryVo vo){
        return userService.list(vo);
    }
}

8:配置文件根据自己的情况编写即可，我这里用的是nacos配置中心注册的服务，因为我船舰的是微服务架构，UserService只是一个用户模块的服务
9：单元测试

@Test
    public void ervsd(){
        UserQueryVo vo = new UserQueryVo();
        vo.setPage(0);
        vo.setSize(15);
        System.out.println(userService.list(vo).getContent());
    }

结果：

[UserVo(id=123, userName=null, profession=null, grade=null), UserVo(id=575698132303290368, userName=17856419339, profession=计算机, grade=1704), UserVo(id=575716833031299072, userName=17856419331, profession=计算机, grade=1704), UserVo(id=576000665194274816, userName=17856419332, profession=计算机, grade=1703), UserVo(id=576000781602988032, userName=17856419333, profession=计算机, grade=1703), UserVo(id=576000899173523456, userName=17856419334, profession=计算机, grade=1702), UserVo(id=576001007231377408, userName=17856419335, profession=计算机, grade=1702), UserVo(id=576001227939848192, userName=17856419336, profession=计算机, grade=1701), UserVo(id=576001356105195520, userName=17856419337, profession=计算机, grade=1701), UserVo(id=576001504025714688, userName=17856419338, profession=计算机, grade=1701), UserVo(id=576001653640732672, userName=17856419310, profession=计算机, grade=1701), UserVo(id=576001828031504384, userName=17856419311, profession=计算机, grade=1704), UserVo(id=576337740011610112, userName=17856419312, profession=计算机, grade=1703)]
共13条数据，表里面也就13条，sql里要求了好多参数，我现在没传，它就默认没这个条件，即查询的是全部

现在加一些参数

@Test
    public void ervsd(){
        UserQueryVo vo = new UserQueryVo();
        vo.setPage(0);
        vo.setSize(15);
        vo.setProfession("计算机");
        vo.setGrade("1701");
        System.out.println(userService.list(vo).getContent());
    }

结果:

[UserVo(id=576001227939848192, userName=17856419336, profession=计算机, grade=1701), UserVo(id=576001356105195520, userName=17856419337, profession=计算机, grade=1701), UserVo(id=576001504025714688, userName=17856419338, profession=计算机, grade=1701), UserVo(id=576001653640732672, userName=17856419310, profession=计算机, grade=1701)]
共四条数据，出了分页参数，还加了两个条件专业和班级，它就自动加进去了，是不是很简洁

这种写法比传统的specification或者nativesql拼接字符串查询都要简洁，代码量少，通俗易懂。