Regex Replacement lookhead

Question

I am not able to do a replacement regex

for example I have the email

[email protected]

and I want to replace

f****e@g***l.com

I already got the start

(?<=.).(?=[^@]*?.@)|(?<=\@.).

Below a link from where I am testing

REGEX

Answer 1

With a bit of further tweaking on the pattern, you could achieve that:

"[email protected]".replaceAll("(?<=[^@])[^@](?=[^@]*?.[@.])", "*");

This will give you f****e@g***l.com.

A possibly more efficient, and more readable solution might be finding the indexes of @ and ., and putting together the desired result from substrings:

int atIndex = email.indexOf('@');
int dotIndex = email.indexOf('.');
if (atIndex > 2 && dotIndex > atIndex + 2) {
  String masked = email.charAt(0)
    + email.substring(1, atIndex - 1).replaceAll(".", "*")
    + email.substring(atIndex - 1, atIndex + 2)
    + email.substring(atIndex + 2, dotIndex - 1).replaceAll(".", "*")
    + email.substring(dotIndex - 1);
  System.out.println(masked);
}

Answer 2

I found this: (?<=.)([^@])(?!@)(?=.*@)|(?<!@)([^@])(?!.*@)(?!\.)(?=.*\.)

Demo