EntityManager 使用 Pageable 分页

参考：https://blog.csdn.net/qq_43948440/article/details/110877496

一，通用方法

/**
     * 无参查询，sql语句
     * @param querySql   sql
     * @param pageable   Pageable.unpaged() 代表不分页
     * @param destType   需要映射的类型
     * @param <U>
     * @return
     */
 
@Override
    public <U> Page<U> findPage(String querySql, Pageable pageable,final Class<U> destType) {
        Query query=em.createNativeQuery(querySql);
        Page<U> page=findPage(query,pageable,destType);
        return page;
    }
 
/**
     * 无参查询，sql语句
     * @param quer       javax.persistence.Query
     * @param pageable   Pageable.unpaged() 代表不分页
     * @param destType   需要映射的类型
     * @param <U>
     * @return
     */
    @Override
    public <U> Page<U> findPage(Query query, Pageable pageable, Class<U> destType) {
        String countSql = "SELECT COUNT(*)  FROM ( "+ ((NativeQueryImpl) query).getQueryString() +" ) getcount";
        Query countQuery = em.createNativeQuery(countSql);
 
        for (Parameter param : query.getParameters())
        {
            countQuery.setParameter(param.getName(),query.getParameterValue(param.getName()));
        }
        BigInteger totalCount = (BigInteger) countQuery.getSingleResult();
 
        if(pageable.isPaged()) {
            query.setFirstResult((int) pageable.getOffset());
            query.setMaxResults(pageable.getPageSize());
        }
        query.unwrap(NativeQueryImpl.class).setResultTransformer(Transformers.ALIAS_TO_ENTITY_MAP);
        List resultList = query.getResultList();
        Page<U> page = new PageImpl<>(resultList,pageable,totalCount.longValue());
        return page;
    }

二，调用

//分页  Pageable pageable = PageRequest.of(pageIndex, pageSsize(), Sort.Direction.DESC, "create_time");
//不分页 Pageable pageable=Pageable.unpaged() ;
 
public Page<entityDTO> findMachineToPlan(String a,Integer b,Pageable pageable) {
        String sql = "select * from table where a=:a and b=:b";
        Query query = em.createNativeQuery(sql);
        query.setParameter("a", a);
        query.setParameter("b", b);
 
        Page<mac_machine_screen_res> page = findPage(query,pageable,entityDTO.class);
        return page;
}