Grabs the player count (on request), and allows outside access through a public getter.

PlayerCountPoller.java

public class PlayerCountPoller implements PluginMessageListener {

	private int count;

	public void requestUpdate() {
		List<? extends Player> players = Bukkit.getOnlinePlayers();
		if (players.isEmpty()) {
			return;
		}
        Player player = players.get(0); // Just grab the first
		ByteArrayDataOutput out = ByteStreams.newDataOutput();
		out.writeUTF("PlayerCount");
		out.writeUTF("ALL");
		player.sendPluginMessage(this, "BungeeCord", out.toByteArray());
	}

	@Override
	public void onPluginMessageReceived(String channel, Player player, byte[] message) {
		if (!channel.equals("bungee") {
			return;
		}

		ByteArrayDataInput in = ByteStreams.newDataInput(message);
	    String subchannel = in.readUTF();
	    if (subchannel.equals("PlayerCount")) {
	    	in.readUTF(); // I could read the server name, if I cared
			this.count = in.readInt();
	    }
	}

	public int getLastKnownCount() {
		return this.count;
	}
}