regex password validation

Question

How would I get this so it would check for 2 or more digits in the String? Invoking matches on the String s.

s.matches("^[a-zA-Z0-9]{8,}$");

Answer 1

This should do it...

^(?=.*[0-9].*[0-9])[a-zA-Z0-9]{8,}$

The only change I made is adding this (?=.*[0-9].*[0-9]) which is a positive lookahead that will try to find the first 2 digits within the password. If it's satisfied, then the regular expression will proceed as usual.

Now, I just thought I'd point out that your regular expression will disallow special characters (punctuation and such). In practice, some people like to enter weird characters like this in their passwords.

So you might consider something more like this...

^(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9]).{8,}$

This will allow special characters while also ensuring at least one capital letter, one lower case letter, and one number exist in the password. This is just an example of a strong password regular expression I wrote awhile back, and you could certainly relax those restrictions a bit if you so desired.