code: private void doGroupMessage(final JsonObject message) {
      String groupID = message.getString("group");
      DefaultConnectionInputGroup group = groups.get(groupID);
      if (group != null) {
        Object value = deserializer.deserialize(message);
        if (value != null) {
          if (log.isDebugEnabled()) {
            log.debug(String.format("%s - Group received: Group[group=%s, id=%d, message=%s", this, groupID, message.getLong("id"), value));
          }
          group.handleMessage(value);
        }
      }
    }
docs: Handles a group message.