There's also a question of what we're really trying to validate, IMHO. All of these regex patterns will tell you that a string looks like a URL, but they won't

There's also a question of what we're really trying to validate, IMHO. All of these regex patterns will tell you that a string looks like a URL, but they won't actually tell you if: There's any web server listening at that particular URL; Whether that server has the resource in that location; If that server is reachable from where you want to fetch it; etc.