JPA中实现动态分组查询，即输入几个筛选参数就按照几个参数进行分组查询，但是不知道输入的是几个参数，要实现动态的分组查询，用CriteriaQuery实现。
Repository：
@Repository
public interface TestCostRepository extends JpaRepository<TestCost, Integer>, JpaSpecificationExecutor<TestCost> {
}
TestCostService：
public interface TestCostService {List<Map<String,String>> dynamicGroupBy(List<String> groupByParams,String sumParam);
}
TestCostServiceImpl：
@Service
public class TestCostServiceImpl implements TestCostService {@AutowiredTestCostRepository repository;@Autowiredprivate EntityManagerFactory entityManagerFactory;@Overridepublic List<Map<String, String>> dynamicGroupBy(List<String> groupByParams, String sumParam) {EntityManager entityManager = entityManagerFactory.createEntityManager();CriteriaBuilder cb = entityManager.getCriteriaBuilder();CriteriaQuery<Object[]> query = cb.createQuery(Object[].class);Root<TestCost> root = query.from(TestCost.class);List<Expression<?>> expressions = new ArrayList<>();for (String field : groupByParams) {expressions.add(root.get(field));}query.groupBy(expressions.toArray(new Expression[0]));Expression<BigDecimal> sumExpression = cb.sum(root.get(sumParam));expressions.add(sumExpression);query.multiselect(expressions.toArray(new Expression[0]));TypedQuery<Object[]> typedQuery = entityManager.createQuery(query);List<Object[]> resultList = typedQuery.getResultList();List<Map<String, String>> returnList = new ArrayList<>();for (Object[] result : resultList) {Map<String, String> returnMap = new LinkedHashMap<>();returnMap.put("name", (String) result[0]);returnMap.put("gender", (String) result[1]);returnMap.put("cost", result[2].toString());returnList.add(returnMap);}return returnList;}}
)
