ip address in java

Question

Hey,

I've been asked to activate a certain piece of code if i was in my college. So I need to find the iP of where i am to match to my colleges iP. Was wonderng how to do this in java? I have already tried a loop back interface.

Answer 1

By using NetworkInterface.getNetworkInterfaces() and calling getInetAddresses() on each interface, you can see all IP addresses assigned to your computer. To check if you have an IP in your university's range, you could do something like this:

boolean onCampusNetwork() {
    for(Enumeration<NetworkInterface> ifaces = NetworkInterface.getNetworkInterfaces(); ifaces.hasMoreElements();) {
        NetworkInterface iface = ifaces.nextElement();
        for(Enumeration<InetAddress> addresses = iface.getInetAddresses(); addresses.hasMoreElements;) {
            InetAddress address = addresses.nextElement();
            // return true if address is in the university's range; something like:
            if(address.toString().startsWith("10.0")) {
                return true;
            }
        }
    }
    // None of the IP addresses were in the university's range.
    return false;
}

I haven't run this code, but it should do what you need.

Answer 2

Isn't there supposed to be some kind of protocol for automatic proxy discovery and configuration? Does your college have this already setup? Then it would be better if your code discovered the correct settings and had an option to override the settings.

Answer 3

There are all kinds of websites out there that will give you your public ip (or the public IP of your gateway, which I assume is what you want). You could tell the program to make an HTTP connection to one of those sites and get the page with the info on it. Since these sites have a very predictable format, the result would be very easy to parse with a regex or two. This only works if you have an internet connection though.

Alternatively, you could have the program try to connect to one of your college's intranet servers. If it can make the connection to a site that is not accessible to the outside world, it's on the LAN.