How can I use Regex in Java to get the first and middle character of the username part of an email?

Question

I want to mask email address like below.

Input: [email protected]; [email protected]; [email protected];

Output: ts@gmail.com; hw@yahoo.co.in; i*i**@hotmail.com;

Below Regex is excluding domain part but masking all characters in first part, except first character.

input.replaceAll("(?<=.{1}).(?=[^@]*?@)","X");

like [email protected] to [email protected]

I wanted to print a character in middle of the local-part like [email protected]

FYI -

I want to get first and middle character (random middle character in case of even length(4/6/8 characters).

Like below.

[email protected] -> A & p characters

[email protected] --> B & t

[email protected] -> k&a or k&t