Map使用foreach遍历方式，Map获取第一个键值

List<Map<String, Object>> mapList = new ArrayList<>();
  for (Map.Entry<String,Object> entry : openDateMap.entrySet()) {
   Map<String, Object> paramMap = new HashMap<>();
   paramMap.put(entry.getKey(),entry.getValue());
   mapList.add(paramMap);
  }
  Collections.sort(mapList, new Comparator<Map<String, Object>>() {
   @Override
   public int compare(Map<String, Object> o1, Map<String, Object> o2) {
    String key1 = (String) o1.keySet().toArray()[0];
    String key2 = (String) o2.keySet().toArray()[0];
    String d1 = (String)o1.get(key1);
    String d2 = (String)o2.get(key2);
    return ReportUtil.compareDateStr(d1, d2, "yyyy-MM-dd", new Date());
   }
  });
  for (Map<String, Object> map: mapList) {
   String projectId = (String) map.keySet().toArray()[0];
   if(!projectIdList.contains(projectId)){
    projectIdList.add(projectId);
   }
  }