stream流分組

   List<Credential> credentials = SqlUtil.getMapToList(entityManager, stringBuilder.toString(), Credential.class);
        List<List<Credential>> groupList = new ArrayList<>();
        credentials.stream().collect(Collectors.groupingBy(Credential::getPaymentMethod, Collectors.toList()))
                .forEach((paymentMethod, fooListByName) -> groupList.add(fooListByName));