Question

I’m trying to validate a e-mail string in Java but I’m getting trouble to validate when this string has two or more special chars toghether, which is not a valid e-mail.

My if that does this validation is the following:

if (email.matches("(._\'!#$%&*+-\\/=?{|}~`^_-)\\1+")) {
    return false;
}

Example for the output:

this_e-mail’[e-mail] – return true (CORRECT)

this_e-mail_isn”[e-mail] – return true (WRONG)

Obviously there’s something wrong with my regular expression.

But I looked all over the internet to find some answer but didn’t succeeded.

I’ve just read that using the “\1+” before expression, it was supposed to do this validation, but apparently it doesn’t.

Thanks in advance for the answers!

Answer 1

I am not at all sure about your requirement. Email validation should be more than just this.

However, if you want to detect whether a string has 2 special characters consecutively or not, you can use

!string.matches("^.*([._\'!#$%&*+\\\\/=?{|}~`\\^-])\\1.*$") // It will invalidate the case that 2 consecutive characters are the same. e.g. not__valid, but it will give OK for va+-lid
OR
!string.matches("^.*[._\'!#$%&*+\\\\/=?{|}~`\\^-]{2}.*$") // Any sequence of consecutive special characters will be invalidate. e.g. not_+valid

Note that I logically negate the result. I’m matching the string if it contains consecutive characters.

I have tested and rectify the error in earlier revision.