Regular expression that matches valid IPv6 addresses

Answer 1

Regexes for ipv6 can get really tricky when you consider addresses with embedded ipv4 and addresses that are compressed, as you can see from some of these answers.

The open-source IPAddress Java library will validate all standard representations of IPv6 and IPv4 and also supports prefix-length (and validation of such). Disclaimer: I am the project manager of that library.

Code example:

        try {
            IPAddressString str = new IPAddressString("::1");
            IPAddress addr = str.toAddress();
            if(addr.isIPv6() || addr.isIPv6Convertible()) {
                IPv6Address ipv6Addr = addr.toIPv6();
            }
            //use address
        } catch(AddressStringException e) {
            //e.getMessage has validation error
        }