public void joinRoomChat(QBDialog dialog)
     throws XMPPException, SmackException, QBResponseException {
   QBGroupChat roomChat = createChatIfNotExist(dialog);
   if (!roomChat.isJoined()) {
     DiscussionHistory history = new DiscussionHistory();
     history.setMaxStanzas(0);
     roomChat.join(history);
   }
 }
 public static MultiUserChat joinRoom(ImConnection talkConnection, String roomName, String user) {
   try {
     // 使用XMPPConnection创建一个MultiUserChat窗口
     MultiUserChat muc = getMultiUserChat(talkConnection, roomName);
     // 聊天室服务将会决定要接受的历史记录数量
     DiscussionHistory history = new DiscussionHistory();
     history.setMaxStanzas(0);
     // 用户加入聊天室
     muc.join(user);
     System.out.println("会议室加入成功........");
     return muc;
   } catch (Exception e) {
     e.printStackTrace();
     System.out.println("会议室加入失败........");
     return null;
   }
 }