Java – IP Address to Integer and back

Many applications store the IP Address as an integer.  This makes it easy to perform mathematical operations on it (say, adding 1024 hosts to a subnet to get min/max addresses, etc).

Currently, I am implementing IPPlan to my toolset, to help me manage all my IP’s and subnets, and make it easy for others to request IP’s.  However, I didn’t want to duplicate the IP’s in use.  I wanted my current network management system to FEED the hosts it already knows into IPPlan.

Easy, I’ll just run a daily SQL to update the IPPlan database.  The issue is, my NMS stores the IP Address as a String, and IPPlan stores it as an integer.

So, taking bits and pieces off the internet, here are a couple of cool Java methods that helped me accomplish this:

From Limewire’s IP.java, here is converting an existing Integer to String:

public static String intToIp(int i) {
        return ((i >> 24 ) & 0xFF) + "." +
               ((i >> 16 ) & 0xFF) + "." +
               ((i >>  8 ) & 0xFF) + "." +
               ( i        & 0xFF);
    }

From Justin-Cook.com, here is converting an existing String to Integer:

public static Long ipToInt(String addr) {
        String[] addrArray = addr.split("\\.");

        long num = 0;
        for (int i=0;i<addrArray.length;i++) {
            int power = 3-i;

            num += ((Integer.parseInt(addrArray[i])%256 * Math.pow(256,power)));
        }
        return num;
    }