code: public static Map<String, String> getNodeHost(Map<String, SupervisorInfo> supInfos) {
          Map<String, String> rtn = new HashMap<>();
          for (Entry<String, SupervisorInfo> entry : supInfos.entrySet()) {
              SupervisorInfo superInfo = entry.getValue();
              String supervisorId = entry.getKey();
              rtn.put(supervisorId, superInfo.getHostName());
          }
          return rtn;
      }
docs: get Map<supervisorId, hostname>