Spring Data JPA 之分页查询

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JPA的分页查询确实使用起来确实很简单，但理解起来有点困难，此处只是实现JPA分页的代码块。

定义实体类：

@Entity
@Table(name = "t_pub_info")
@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public class InfoPO implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
	
    @Column(name ="name")
    private String name;

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

    @Column(name = "pub_time")
    private Date pubTime;

    @Column(name = "depict")
    private String depict;
	
	@Column(name ="city_id")
	private Long cityId;

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

    Getter...
    Setter...
}

定义DAO：

public interface InfoDao extends JpaRepository<InfoPO, Long>, JpaSpecificationExecutor<InfoPO> {

}

定义接口：

@SuppressWarnings(value = "unused")
@RestController
@RequestMapping(value = "/info")
public class InfoController {
	
    @Autowired
    InfoService infoService;

    @GetMapping(value = "/list")
    Object queryInfoList(@RequestParam(value = "pageNo", required = false, defaultValue = "0") Integer pageNo,
                          @RequestParam(value = "pageSize", required = false, defaultValue = "5") Integer pageSize,
                          @RequestParam(value = "status", required = false) String status,
                          @RequestParam(value = "priority", required = false) String priority,
                          @RequestHeader("city_id")Integer cityId) {
        return infoService.queryInfoList(pageNo, pageSize, priority,cityId,String status);
    }
}

定义service

public interface InfoService {
    Object queryinfoList(Integer pageNo, Integer pageSize, String priority,Integer cityId,String status);
}

实现service

@Service
public class InfoServiceImpl implements InfoService {
    protected static final int PAGE_SIZE = 5;

    @Autowired
    InfoDao infoDao;

    public Object queryInfoList(Integer pageNo, Integer pageSize, String priority,Integer cityId,String status) {

        //验证city_id
        if(cityId == null){
            throw new Exception("city id necessary");
        }

        Integer currentPage = pageNo  == null ? 0 : pageNo;

        Page<InfoPO> page = infoDao.findAll((Root<InfoPO> root, CriteriaQuery<?> cq, CriteriaBuilder cb) -> {
            //添加分页筛选条件
            List<Predicate> predicates = new ArrayList<>();
            if (priority != null) {
                predicates.add(cb.equal(root.get("priority"), priority));
            }
            if (status != null) {
                String statusName = status;
                if (StringUtils.isNotBlank(statusName)) {
                    predicates.add(cb.equal(root.get("status"), statusName));
                }
            }

            if (cityId != null) {
                predicates.add(cb.equal(root.get("cityId"), cityId));
            }

            return cb.and(predicates.toArray(new Predicate[]{}));
        }, new PageRequest(currentPage, pageSize, new Sort(Sort.Direction.DESC, "pubTime")));
        
		//获取页面数据以及分页数据
		List<InfoPO> infos = page.getContent();
        Integer totalPage = page.getTotalPages();
        Long totalElement = page.getTotalElements();
       
        return infos;
    }
}