docs: private void buildTrackerAddresses() {
          Set<InetSocketAddress> addressSet = new HashSet<InetSocketAddress>();
          for (String item : trackerList) {
              if (StringUtils.isBlank(item)) {
                  continue;
              }
              String[] parts = StringUtils.split(item, ":", 2);
              if (parts.length != 2) {
                  throw new IllegalArgumentException(
                          "the value of item \"tracker_server\" is invalid, the correct format is host:port");
              }
              InetSocketAddress address = new InetSocketAddress(parts[0].trim(), Integer.parseInt(parts[1].trim()));
              addressSet.add(address);
          }
          // 放到轮询圈
          for (InetSocketAddress item : addressSet) {
              TrackerAddressHolder holder = new TrackerAddressHolder(item);
              trackerAddressCircular.add(holder);
              trackerAddressMap.put(item, holder);
          }
  
      }