How can I detect if a network card is not connected with Java without delay?

Question

It there an API (NetworkInterface, InetAddress, etc) in Java with which I can detect that a network card is not connected.

The problem is that addressing some of the network API has a large timeout. But if the network card is not connected to any cable then we can skip it. The problem seems only to occur with Windows 7.

Answer 1

I had this same problem. I ended up using this:

Enumeration<NetworkInterface> eni = NetworkInterface.getNetworkInterfaces();
        while(eni.hasMoreElements()) {
            Enumeration<InetAddress> eia = eni.nextElement().getInetAddresses();
            while(eia.hasMoreElements()) {
                InetAddress ia = eia.nextElement();
                if (!ia.isAnyLocalAddress() && !ia.isLoopbackAddress() && !ia.isSiteLocalAddress()) {
                    if (!ia.getHostName().equals(ia.getHostAddress()))
                        return true;
                }
            }
        }

Works with Java 5+. Also indirectly checks DNS (by comparing names/addresses).

Answer 2

You could use some java system properties to set up the default time out for socket connection using

sun.net.client.defaultConnectTimeout

(all properties here)

But it seems to me that checking wether a specific Medium Access Controller is present or not is the job of the underlying OS. I can't tell you much about windows 7, I got a good OS since 12 years now (linux).

Regards, Stéphane