自动刷新Java中连接的IP地址列表

Question

I'm writing some code that sends/receives information from computers connected to the same network. I have a method that gets the IP of the online computers at that exact moment, but I need to refresh the list when a new IP appears/disappears.

I don't think having a thread and while (true) calling the method is the best solution. And I can't think of anything else - any suggestions?

Here is the sample of the code I use to search for active computers on the network:

public List<String> searchApps() {
    List<AddressServiceTypePair> ip = this.networkController.getDiscovered();  //returns an ArrayList<AddressServiceTypePair>

    onlineApps.clear();
    for (AddressServiceTypePair service : ip) {
        onlineApps.add(service);
    }

    List<String> list = new ArrayList<>();
    for (AddressServiceTypePair aux : onlineApps) {
        list.add(aux.getIP());
    }
    return list;
}

Answer 1

It is difficult to generalize based on the unclear code sample posted. However, I'm assuming you are writing some type of client and server code. There is no simple way to be notified of an added/removed computer on the network. I would be surprised if you needed an up-to-the- moment list of IPs. You could put your IP-discovering method in an infinite loop and simply include Thread.sleep(milliseconds); in your loop.

If you really do need extremely up-to-date information, you could have each connected computer also connect to a Socket on another port in a separate thread, then try to read from the Socket - that way you get an Exception as soon as the Socket closes. You can add the IP of the client when the Socket is created, and your catch block can then update your list of active IPs when the Socket closes, signaling that client is no longer connected.