How can I add two Strings containing hexadecimal-numbers without converting them to int?

I have a hexadecimal number in a String which is too large to convert to int and long and want to add the value of another hexadecimal number. So let's say I have this number:

String hex1 = "0xf27f2029f9c103f77be78b9591c1ab27167858d27d789cd3ea8a270c67ea5d91";

And want to add:

int hex2 = 0x1;  or  String hex2 = "0x1";

I know this question has been asked allready How to subtract or add two hexadecimal value in java but the answers don't work for me because they all involve conversion to int.

You can do it as follows:

import java.math.BigInteger;

public class Main {
    public static void main(String[] args) {
        String hex1 = "0xf27f2029f9c103f77be78b9591c1ab27167858d27d789cd3ea8a270c67ea5d91";
        String hex2 = "0x1";
        System.out.println(
                "In decimal: " + new BigInteger(hex1.substring(2), 16).add(new BigInteger(hex2.substring(2), 16)));
        System.out.println("In hexdecimal: "
                + new BigInteger(hex1.substring(2), 16).add(new BigInteger(hex2.substring(2), 16)).toString(16));
    }
}

Output:

In decimal: 109684320921920394042076832992416841330182602685967688614501993994243850001810
In hexdecimal: f27f2029f9c103f77be78b9591c1ab27167858d27d789cd3ea8a270c67ea5d92