java8 转map key相同 值逗号隔开

if(CollUtil.isNotEmpty(tpartDingOrgList)){
    orgMap = tpartDingOrgList.stream().collect(Collectors.toMap(arr -> arr.getOrganizationUuid(),arr ->CollUtil.newArrayList(arr.getBelongOuUuid()), (List<String> oldList, List<String> newList) -> {

        oldList.addAll(newList);
        return oldList;
    }));
}

List<String> deptNameList = finalOrgMap.get(deptId);

String deptName = Convert.toStr(deptNameList,",");

Map<Long, String> buildSkyscraperMap = new HashMap<>();
if(CollUtil.isNotEmpty(buildSkyscraperList)){
   buildSkyscraperMap = buildSkyscraperList.stream().collect(Collectors.toMap(BuildSkyscraper::getId, s -> Optional.ofNullable(s.getBuildName()).orElse("无"),(a,b)->a));
}