How to Determine Internet Network Interface in Java

Question

How do you determine which network interface is connected to the internet using Java? For example, I run

InetAddress.getLocalHost().getHostAddress();
         


        

Answer 1

I was bugged by the same problem for a quite a bit and eventhough the inital question was asked ages ago I'll append my take on ths issue anyway. The ironic thing is that the answer was provided along with the question.
It is: siteLocal = true
Here is what worked for me

1. Get all network interfaces

   NetworkInterface.getNetworkInterfaces();
   

2. Single out those that are currently down (just reduces the number of runs)

   if(interface.isUp()){}
   

3. Get the InetAddresses of the interfaces you just singled out

   interface.getInetAddresses();
   

4. Check those addresses if they are site local addresses

   if(inetAddress.isSiteLocal()){}
   

That should give you one/all InetAddress(es) - and the network interface(s) that is/are linked to your local network.
Site local is defined to use addresses from these networks: 10.0.0.0, 172.16.0.0, 192.168.0.0 while VirtualBox adapters and others usually use the 169.254.0.0 link-local addresses. IPv6 also implements the site local concept, so it's best to focus on IPv4 here. On a regular end user machine this should work rather well and return just the one physical interface.