How to convert IP address range to CIDR in Java?

Question

I am trying to convert the IP address range into the CIDR notation in Java. Can someone provide an example of how this can be achieved?

I used the SubnetUtils for converting the CIDR to the IP address range, but I can't figure out the other way around.

For example: (using http://ip2cidr.com/)

Input 1: 5.10.64.0

Input 2: 5.10.127.255

Result: 5.10.64.0/18

Answer 1

The open-source IPAddress Java library can do this for you. Disclaimer: I am the project manager of the IPAddress library.

Here is sample code to do it:

static void toPrefixBlocks(String str1, String str2) {
    IPAddressString string1 = new IPAddressString(str1);
    IPAddressString string2 = new IPAddressString(str2);
    IPAddress one = string1.getAddress(), two = string2.getAddress();
    IPAddressSeqRange range = one.spanWithRange(two);
    System.out.println("starting with range " + range);
    IPAddress blocks[] = range.spanWithPrefixBlocks();
    System.out.println("prefix blocks are " + Arrays.asList(blocks));
}

This is how you would use IPAddress to produce the range from the original CIDR string:

static String[] toRange(String str) {
    IPAddressString string = new IPAddressString(str);
    IPAddress addr = string.getAddress();
    System.out.println("starting with CIDR " + addr);
    IPAddress lower = addr.getLower(), upper = addr.getUpper();
    System.out.println("range is " + lower + " to " + upper);
    return new String[] {lower.toString(), upper.toString()};
}

For your example, we run this code:

String strs[] = toRange("5.10.64.0/18");
System.out.println();
toPrefixBlocks(strs[0], strs[1]);

The output is:

starting with CIDR 5.10.64.0/18
range is 5.10.64.0/18 to 5.10.127.255/18

starting with range 5.10.64.0 -> 5.10.127.255
prefix blocks are [5.10.64.0/18]