Xmpp获取离线消息

文章只是选取了其中一段，无XMPP基础的人可能看起来有点复杂;

假设我们注册了一个用户，用户名叫shimiso，那么我们如何让shimiso这个用户一登陆就取到离线消息呢？

PPConnection.DEBUG_ENABLED = false;
    AccountManager accountManager;
    final ConnectionConfiguration connectionConfig = new ConnectionConfiguration(
        "192.168.1.78", Integer.parseInt("5222"), "csdn.shimiso.com");

    // 允许自动连接
    connectionConfig.setReconnectionAllowed(true);
    connectionConfig.setSendPresence(false);//不要告诉服务器自己的状态
    Connection connection = new XMPPConnection(connectionConfig);
    try {
      connection.connect();// 开启连接
      accountManager = connection.getAccountManager();// 获取账户管理类
    } catch (XMPPException e) {
      throw new IllegalStateException(e);
    } 
    connection.login("shimiso", "123","SmackTest"); 
    OfflineMessageManager offlineManager = new OfflineMessageManager(
        connection);
    try {
      Iterator it = offlineManager
          .getMessages();

      System.out.println(offlineManager.supportsFlexibleRetrieval());
      System.out.println("离线消息数量: " + offlineManager.getMessageCount());

      Map> offlineMsgs = new HashMap>();

      while (it.hasNext()) {
        org.jivesoftware.smack.packet.Message message = it.next();
        System.out
            .println("收到离线消息, Received from 【" + message.getFrom()
                + "】 message: " + message.getBody());
        String fromUser = message.getFrom().split("/")[0];

        if (offlineMsgs.containsKey(fromUser)) {
          offlineMsgs.get(fromUser).add(message);
        } else {
          ArrayList temp = new ArrayList();
          temp.add(message);
          offlineMsgs.put(fromUser, temp);
        }
      }

      // 在这里进行处理离线消息集合......
      Set keys = offlineMsgs.keySet();
      Iterator offIt = keys.iterator();
      while (offIt.hasNext()) {
        String key = offIt.next();
        ArrayList ms = offlineMsgs.get(key);

        for (int i = 0; i < ms.size(); i++) {
          System.out.println("-->" + ms.get(i));
        }
      }

      offlineManager.deleteMessages();
    } catch (Exception e) {
      e.printStackTrace();
    }
    offlineManager.deleteMessages();//删除所有离线消息
    Presence presence = new Presence(Presence.Type.available);
        		nnection.sendPacket(presence);//上线了
        		nnection.disconnect();//关闭连接

运行结果：

这里我们需要特别当心的是先不要告诉openfire服务器你上线了，否则永远也拿不到离线消息，用下面老外的话将就是在你上线之前去获取离线消息，这么设计是很有道理的。

The OfflineMessageManager helps manage offline messages even before the user has sent an available presence. When a user asks for his offline messages before sending an available presence then the server will not send a flood with all the offline messages when the user becomes online. The server will not send a flood with all the offline messages to the session that made the offline messages request or to any other session used by the user that becomes online.

同时拿到离线消息以后删除离线消息offlineManager.deleteMessages();，同是通知服务器自己上线了。