不幸的是，JPA没有提供一种标准的方法来检索中的结果
Map。但是，通过遍历结果列表来手动构建地图非常简单：
TypedQuery<Object[]> q = getEntityManager().createQuery( "SELECt c.id, count(p.id) " + "FROM Product p LEFT JOIN p.category c " + "WHERe p.seller.id = :id " + "GROUP BY c.id", Object[].class).setParameter("id", id);List<Object[]> resultList = q.getResultList();Map<String, Long> resultMap = new HashMap<String, Long>(resultList.size());for (Object[] result : resultList) resultMap.put((String)result[0], (Long)result[1]);
