What are the Java regular expressions for matching IPv4 and IPv6 strings?

Question

Looking for a string to pass to String#matches(String) that will match IPv4, and another to match IPv6.

Answer 1

Regexes for ipv6 can get really tricky when you consider addresses with embedded ipv4 and addresses that are compressed.

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();
} catch(AddressStringException e) {
    //e.getMessage has validation error
}