Regular Expression in Java for validating username

Question

I'm trying the username chains in Java with following rules:

Length >=3
Valid characters: a-z, A-Z, 0-9, points, dashes and underscores.

Could someone help me with the regular expression?

score 18 · Accepted Answer · edited Nov 07 '18 at 00:15

18

try this regular expression:

^[a-zA-Z0-9._-]{3,}$

edited Nov 07 '18 at 00:15

wisbucky

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answered Jul 21 '11 at 20:39

sarkiroka

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[a-zA-Z0-9_.-]{3,} is more accurate as he wants to include "points dashes and underscores". See http://stackoverflow.com/questions/3028642/regular-expression-for-letters-numbers-and – Grambot Jul 21 '11 at 20:41
2

@TheCapn: I fixed it as you were writing your comment. :-) – RichieHindle Jul 21 '11 at 20:43
1

You should add start `^` and end-of-string `$` anchors for validation regexes like these (although the Java `.matches()` method does do this implicitly). – ridgerunner Jul 21 '11 at 23:48

score 5 · Answer 2 · answered Jul 21 '11 at 20:44

5

Sarkiroka solution is right, but forgot the dash and the point should be escaped.

You should add as \ to escape it, but mind that in Java the backslash is itself used to escape, so if you are writing the regex in a java file, you should write

String regex = "[a-zA-Z0-9\\._\\-]{3,}";

Note the double back slashes.

answered Jul 21 '11 at 20:44

Simone Gianni

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No need to escape `.`, and probably no need to escape `-` either since it's last in the class (but I'm unsure how Java handles this). – Qtax Jul 21 '11 at 21:33

score 4 · Answer 3 · answered Dec 04 '15 at 08:59

BTW, if there is an extra requirement: the starting letter of the username must be a character, you can write

try {
    if (subjectString.matches("\\b[a-zA-Z][a-zA-Z0-9\\-._]{3,}\\b")) {
        // Successful match 

    } else {
        // No match 

    }
} catch (PatternSyntaxException ex) {
    // Invalid regex 

}

Based on an example here.

Emmanuel Bourg · Answer 4 · 2011-07-22T12:59:39.813

1

What about:

    username.matches("[a-zA-Z0-9.\\-_]{3,}")

edited Jul 22 '11 at 12:59

answered Jul 21 '11 at 20:43

Emmanuel Bourg

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I don't think you have to escape the .-_ characters if they're in the [] but other than that it looks fine, though you should've commented on Richie's answer before posting your own. – 8vius Jul 21 '11 at 20:47
1

The dash must be escaped, but it doesn't matter for the dot. – Emmanuel Bourg Jul 21 '11 at 20:55

Regular Expression in Java for validating username

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