spring data jpa分页查询示例代码

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; 

@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; 

@Repository
public 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); 

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