spring data jpa分頁查詢

最近項目上用就hibernate+spring data jpa，一開始感受還不錯，可是隨着對業務的複雜，要求處理一些複雜的sql，就順便研究了下，把結果記錄下，以便往後查看。用到Specification，須要繼承JpaSpecificationExecutor接口。(下面代碼有的分頁從0開始做爲第一頁，有的從1開始做爲做爲第一頁，我也忘記，請本身測試)

DAO層：

import java.util.List;

import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;

@Repository
public interface CameraInfoRepo extends JpaRepository<CameraInfoPO, String>, JpaSpecificationExecutor<CameraInfoPO> {

    @Query("select c from CameraInfoPO c where c.deviceInfo.id = ?1")
    public List<CameraInfoPO> findCamerasByDeviceId(String listDeviceInfoId);

    //更新以後不清空緩存，在一個事務裏查詢到舊數據(hibernate)
    @Modifying
    @Query(value = "update CameraInfoPO c set c.isEnabled = 1 where c.id = ?1")
    public void updateEnabled(String cameraId);

    //更新以後清空緩存，不保留舊對象(hibernate)
    @Modifying(clearAutomatically = true)
    @Query(value = "update CameraInfoPO c set c.isEnabled = 0 where c.id = ?1")
    public void updateUnEnabled(String cameraId);

    //帶條件的分頁查詢      
    public Page<CameraInfoPO> findByIsEnabled(Integer isEnabled, Pageable pageable);

}

DAO實現層

import java.util.ArrayList;
import java.util.List;

import javax.annotation.Resource;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.TypedQuery;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;

import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.stereotype.Repository;

@Repository
public class CameraInfoRepoImpl {

    @PersistenceContext
    private EntityManager em;

    @Resource
    private CameraInfoRepo cameraInfoRepo;

    public Page<CameraInfoPO> findCameraInfoByPage(Pageable pageable, Integer isEnabled) {

        //CriteriaBuilder,用來構建CritiaQuery的構建器對象
        CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();

        //CriteriaQuery,它包含着查詢語句的條件各個部分，好比：select 、from、where、group by、order by等
        CriteriaQuery<CameraInfoPO> criteriaQuery = criteriaBuilder.createQuery(CameraInfoPO.class);

        //查詢根，用於獲取查詢實例的屬性，經過CriteriaQuery的from方法獲取
        Root<CameraInfoPO> rootFrom = criteriaQuery.from(CameraInfoPO.class);

        //查詢條件
        List<Predicate> predicates = new ArrayList<Predicate>();

        if (null != isEnabled) {
            Predicate predicate = criteriaBuilder.equal(rootFrom.get("isEnabled").as(Integer.class), isEnabled);
            predicates.add(predicate);

        }

        //格式化參數
        criteriaQuery.where(criteriaBuilder.and(predicates.toArray(new Predicate[predicates.size()])));

        //默認按照id排序（從小到大）
        criteriaQuery.orderBy(criteriaBuilder.asc(rootFrom.get("id")));

        //SQL查詢對象
        TypedQuery<CameraInfoPO> createQuery = em.createQuery(criteriaQuery);

        //分頁參數
        Integer pageSize = pageable.getPageSize();
        Integer pageNo = pageable.getPageNumber();

        //計數查詢結果條數
        TypedQuery<CameraInfoPO> createCountQuery = em.createQuery(criteriaQuery);

        // 實際查詢返回分頁對象
        int startIndex = pageSize * pageNo;
        createQuery.setFirstResult(startIndex);
        createQuery.setMaxResults(pageable.getPageSize());
        Page<CameraInfoPO> pageRst =
            new PageImpl<CameraInfoPO>(createQuery.getResultList(), pageable, createCountQuery.getResultList().size());
        return pageRst;

    }

    //製造查詢條件結果(建議存放map)
    private Specification<CameraInfoPO> getWhereClause(final Integer isEnabled) {
        return new Specification<CameraInfoPO>() {
            public Predicate toPredicate(Root<CameraInfoPO> r, CriteriaQuery<?> q, CriteriaBuilder cb) {
                Predicate predicate = cb.conjunction();
                if (null != isEnabled) {

                    predicate = cb.equal(r.get("isEnabled").as(Integer.class), isEnabled);
                }

                return predicate;
            }
        };
    }

    //單表根據查詢條件的分頁
    public Page<CameraInfoPO> findCameraInfoByPageForJpa(Pageable pageable, Integer isEnabled) {

        Specification<CameraInfoPO> spec = getWhereClause(isEnabled);

        Page<CameraInfoPO> pageRst = cameraInfoRepo.findAll(spec, pageable);

        return pageRst;

    }

}

還有另一種就更簡單了，若是隻是根據表裏面的一個或者幾個字段，能夠直接寫jpa實現，不用複雜。

Pageable pageable = new PageRequest(1, 1);

        Page<CameraInfoPO> page = cameraInfoRepo.findByIsEnabled(1, pageable);