spring data jpa 怎么查询一个字段的总和？

不用sql实现，用类似这种方法实现
Long num = taskUserTaskHistoryEditDao.count(new Specification() {
@Override
public Predicate toPredicate(Root root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) {
List predicateList = new ArrayList<>();
predicateList.add(criteriaBuilder.equal(root.get("taskId"),taskId));
criteriaQuery.where(criteriaBuilder.and(predicateList.toArray(new Predicate[]{})));
return criteriaQuery.getRestriction();
}
});

criteriaBuilder里面有个sum的方法

同求