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

Here's a regex to match IPv4 addresses:

\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b

You'll need to escape the backslashes when you specify it as a string literal in Java:

"\\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\b"