Java Quickly check for network connection

Question

My issue is fairly straightforward. My program requires immediate notification if a network connection is lost. I\'m using Java 5, so I\'m unable to use the very handy feature

Answer 1

You need to first create an interface called NetworkListener, for example

public interface NetworkListener {
    public void sendNetworkStatus(String status);
}

Next, create a class and call it NetworkStatusThread, for example

public class NetworkStatusThread implements Runnable {
    List listenerList = new Vector();

    @SuppressWarnings("unchecked")
    public synchronized void addNetworkListener(NetworkListener nl) {
        listenerList.add(nl);
    }

    public synchronized void removeNetworkListener(NetworkListener nl) {
        listenerList.remove(nl);
    }


    private synchronized void sendNetworkStatus(String status) {
        // send it to subscribers
        @SuppressWarnings("rawtypes")
        ListIterator iterator = listenerList.listIterator();
        while (iterator.hasNext()) {
            NetworkListener rl = (NetworkListener)iterator.next();
            rl.sendNetworkStatus(status);
        }
    }

    public void run() {
        while (true) {
        System.out.println("Getting resource status");
        try {
             Thread.sleep(2000);
             System.out.println("Sending resource status to registered listeners");
             this.sendResourceStatus("OK");
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

 }

Then in your class that instantiates the Thread, do this:

NetworkStatusThread netStatus = new NetworkStatusThread();
netStatus.addNetworkListener(this);
Thread t = new Thread(netStatus);
t.Start();

Also, in that class, you need to implement the NetworkListener, in order to get the callbacks.

In your run() method above, you can implement the code by @Ali, but pass my status:

  int timeout = 2000;
  InetAddress[] addresses = InetAddress.getAllByName("www.google.com");
  for (InetAddress address : addresses) {
    if (address.isReachable(timeout))
       this.sendResourceStatus("OK");
    else
       this.sendResourceStatus("BAD");
  }