Conversion IPv6 to long and long to IPv6

You can also use java.net.InetAddress
It works with both ipv4 and ipv6 (all formats)

public static BigInteger ipToBigInteger(String addr) {
    InetAddress a = InetAddress.getByName(addr)
    byte[] bytes = a.getAddress()
    return new BigInteger(1, bytes)
}

An IPv6 address is a 128-bit number as described here. A long in Java is represented on 64 bits, so you need another structure, like a BigDecimal or two longs (a container with an array of two longs or simply an array of two longs) in order to store an IPv6 address.

Below is an example (just to provide you an idea):

public class Asd {

    public static long[] IPToLong(String addr) {
        String[] addrArray = addr.split(":");//a IPv6 adress is of form 2607:f0d0:1002:0051:0000:0000:0000:0004
        long[] num = new long[addrArray.length];
        
        for (int i=0; i<addrArray.length; i++) {
            num[i] = Long.parseLong(addrArray[i], 16);
        }
        long long1 = num[0];
        for (int i=1;i<4;i++) {
            long1 = (long1<<16) + num[i];
        }
        long long2 = num[4];
        for (int i=5;i<8;i++) {
            long2 = (long2<<16) + num[i];
        }
        
        long[] longs = {long2, long1};
        return longs;
    }
    
    
    public static String longToIP(long[] ip) {
        String ipString = "";
        for (long crtLong : ip) {//for every long: it should be two of them

            for (int i=0; i<4; i++) {//we display in total 4 parts for every long
                ipString = Long.toHexString(crtLong & 0xFFFF) + ":" + ipString;
                crtLong = crtLong >> 16;
            }
        }
        return ipString;
    
    }
    
    static public void main(String[] args) {
        String ipString = "2607:f0d0:1002:0051:0000:0000:0000:0004";
        long[] asd = IPToLong(ipString);
        
        System.out.println(longToIP(asd));
    }
}