spring data jpa分页查询

最近项目上用就hibernate+spring data jpa，一开始感觉还不错，但是随着对业务的复杂，要求处理一些复杂的sql，就顺便研究了下，把结果记录下，以便日后查看。用到Specification，需要继承JpaSpecificationExecutor接口。（下面代码有的分页从0开始作为第一页，有的从1开始作为作为第一页，我也忘记，请自己测试）

DAO层：

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;@Repositorypublic 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);        //更新之后不清空缓存，在一个事务里查询到旧数据(hibernate)    @Modifying    @Query(value = "update CameraInfoPO c set c.isEnabled = 1 where c.id = ?1")    public void updateEnabled(String cameraId);        //更新之后清空缓存，不保留旧对象(hibernate)    @Modifying(clearAutomatically = true)    @Query(value = "update CameraInfoPO c set c.isEnabled = 0 where c.id = ?1")    public void updateUnEnabled(String cameraId);        //带条件的分页查询          public Page<CameraInfoPO> findByIsEnabled(Integer isEnabled, Pageable pageable);    }

DAO实现层

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;@Repositorypublic class CameraInfoRepoImpl {        @PersistenceContext    private EntityManager em;        @Resource    private CameraInfoRepo cameraInfoRepo;        public Page<CameraInfoPO> findCameraInfoByPage(Pageable pageable, Integer isEnabled) {                //CriteriaBuilder,用来构建CritiaQuery的构建器对象        CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();                //CriteriaQuery,它包含着查询语句的条件各个部分，比如：select 、from、where、group by、order by等        CriteriaQuery<CameraInfoPO> criteriaQuery = criteriaBuilder.createQuery(CameraInfoPO.class);                //查询根，用于获取查询实例的属性，通过CriteriaQuery的from方法获取        Root<CameraInfoPO> rootFrom = criteriaQuery.from(CameraInfoPO.class);                //查询条件        List<Predicate> predicates = new ArrayList<Predicate>();                if (null != isEnabled) {            Predicate predicate = criteriaBuilder.equal(rootFrom.get("isEnabled").as(Integer.class), isEnabled);            predicates.add(predicate);                    }                //格式化参数        criteriaQuery.where(criteriaBuilder.and(predicates.toArray(new Predicate[predicates.size()])));                //默认按照id排序（从小到大）        criteriaQuery.orderBy(criteriaBuilder.asc(rootFrom.get("id")));                //SQL查询对象        TypedQuery<CameraInfoPO> createQuery = em.createQuery(criteriaQuery);                //分页参数        Integer pageSize = pageable.getPageSize();        Integer pageNo = pageable.getPageNumber();                //计数查询结果条数        TypedQuery<CameraInfoPO> createCountQuery = em.createQuery(criteriaQuery);                // 实际查询返回分页对象        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;            }        //制造查询条件结果(建议存放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;            }        };    }        //单表根据查询条件的分页    public Page<CameraInfoPO> findCameraInfoByPageForJpa(Pageable pageable, Integer isEnabled) {                Specification<CameraInfoPO> spec = getWhereClause(isEnabled);                Page<CameraInfoPO> pageRst = cameraInfoRepo.findAll(spec, pageable);                return pageRst;            }    }

还有另外一种就更简单了，如果只是根据表里面的一个或者几个字段，可以直接写jpa实现，不用复杂

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