Regular expression that matches valid IPv6 addresses

Answer 1

InetAddressUtils has all the patterns defined. I ended-up using their pattern directly, and am pasting it here for reference:

private static final String IPV4_BASIC_PATTERN_STRING =
        "(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\\.){3}" + // initial 3 fields, 0-255 followed by .
         "([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])"; // final field, 0-255

private static final Pattern IPV4_PATTERN =
    Pattern.compile("^" + IPV4_BASIC_PATTERN_STRING + "$");

private static final Pattern IPV4_MAPPED_IPV6_PATTERN = // TODO does not allow for redundant leading zeros
        Pattern.compile("^::[fF]{4}:" + IPV4_BASIC_PATTERN_STRING + "$");

private static final Pattern IPV6_STD_PATTERN =
    Pattern.compile(
            "^[0-9a-fA-F]{1,4}(:[0-9a-fA-F]{1,4}){7}$");

private static final Pattern IPV6_HEX_COMPRESSED_PATTERN =
    Pattern.compile(
            "^(([0-9A-Fa-f]{1,4}(:[0-9A-Fa-f]{1,4}){0,5})?)" + // 0-6 hex fields
             "::" +
             "(([0-9A-Fa-f]{1,4}(:[0-9A-Fa-f]{1,4}){0,5})?)$"); // 0-6 hex fields