import org.jivesoftware.smack.filter.NotFilter; //导入依赖的package包/类
/**
 * Enter a room, as described in XEP-45 7.2.
 *
 * @param nickname
 * @param password
 * @param history
 * @param timeout
 * @return the returned presence by the service after the client send the initial presence in order to enter the room.
 * @throws NotConnectedException
 * @throws NoResponseException
 * @throws XMPPErrorException
 * @see <a href="http://xmpp.org/extensions/xep-0045.html#enter">XEP-45 7.2 Entering a Room</a>
 */
private Presence enter(String nickname, String password, DiscussionHistory history,
                long timeout) throws NotConnectedException, NoResponseException,
                XMPPErrorException {
    StringUtils.requireNotNullOrEmpty(nickname, "Nickname must not be null or blank.");
    // We enter a room by sending a presence packet where the "to"
    // field is in the form "[email protected]/nickname"
    Presence joinPresence = new Presence(Presence.Type.available);
    joinPresence.setTo(room + "/" + nickname);

    // Indicate the the client supports MUC
    MUCInitialPresence mucInitialPresence = new MUCInitialPresence();
    if (password != null) {
        mucInitialPresence.setPassword(password);
    }
    if (history != null) {
        mucInitialPresence.setHistory(history.getMUCHistory());
    }
    joinPresence.addExtension(mucInitialPresence);

    // Wait for a presence packet back from the server.
    StanzaFilter responseFilter = new AndFilter(FromMatchesFilter.createFull(room + "/"
                    + nickname), new StanzaTypeFilter(Presence.class));

    // Setup the messageListeners and presenceListeners *before* the join presence is send.
    connection.addSyncStanzaListener(messageListener, fromRoomGroupchatFilter);
    connection.addSyncStanzaListener(presenceListener, new AndFilter(fromRoomFilter,
                    StanzaTypeFilter.PRESENCE));
    connection.addSyncStanzaListener(subjectListener, new AndFilter(fromRoomFilter,
                    MessageWithSubjectFilter.INSTANCE));
    connection.addSyncStanzaListener(declinesListener, new AndFilter(new StanzaExtensionFilter(MUCUser.ELEMENT,
                    MUCUser.NAMESPACE), new NotFilter(MessageTypeFilter.ERROR)));
    connection.addPacketInterceptor(presenceInterceptor, new AndFilter(new ToFilter(room),
                    StanzaTypeFilter.PRESENCE));
    messageCollector = connection.createPacketCollector(fromRoomGroupchatFilter);

    Presence presence;
    try {
        presence = connection.createPacketCollectorAndSend(responseFilter, joinPresence).nextResultOrThrow(timeout);
    }
    catch (NoResponseException | XMPPErrorException e) {
        // Ensure that all callbacks are removed if there is an exception
        removeConnectionCallbacks();
        throw e;
    }

    this.nickname = nickname;
    joined = true;

    // Update the list of joined rooms
    multiUserChatManager.addJoinedRoom(room);
    return presence;
}