List<HostedRoom> rooms = multiUserChatManager.getHostedRooms(groupChatService.asDomainBareJid());
        for (HostedRoom room :
                rooms) {
            if (room.getJid().getLocalpart().equals(groupChatRoomId)){
                multiUserChat = multiUserChatManager.getMultiUserChat(room.getJid());
            }
        }

if (multiUserChat != null) {
            if (!multiUserChat.isJoined()) {
                multiUserChat.join(connection.getUser().getResourcepart());
            }
        }

public List<Message> getOldMessages() {
    List<Message> oldMessages = new ArrayList<>();
    try {
        Message message = multiUserChat.nextMessage();

        while (message != null) {
            oldMessages.add(message);
            message = multiUserChat.nextMessage();
        }
    } catch (MultiUserChatException.MucNotJoinedException e) {
        e.printStackTrace();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    multiUserChat.addMessageListener(new MessageListener() {
        @Override
        public void processMessage(final Message message) {
            listener.notifyMessage(message.getSubject(), message.getBody());

        }
    });
    return oldMessages;
}