String length and character validation using Java 8 stream API

Question

Find if an input String is valid - the criteria is String length greater than 5 and characters must be a-z, A-Z or 0-9.

Valid strings: aA12Z22, qwerty, ABCDEF0

Not valid: 13A, 12CrW#, @**=_+

I am trying to get it right using Java 8 streams. I have a solution here. The question - is there a better way of doing this (using streams)?

boolean valid = Stream.of(string)
    .flatMapToInt(s -> {
        if (s.length() < 5) return IntStream.of(42); // 42 is a '*' char
        else return s.chars();
        })
    .mapToObj(i -> (char) i)
    .allMatch(c -> Character.isLetterOrDigit(c));
System.out.println(valid);

Why not just use regex: string.matches("[A-Za-z0-9]{5,}")? Streams seem unnecessary, hard and inefficient. — Andy Turner
– Andy Turner, Commented Sep 8, 2017 at 11:06
Can you explain why do you want to do it using stream api? what benefit does it offer compared to regex ? — Sujal Mandal
– Sujal Mandal, Commented Sep 8, 2017 at 11:18

Andy Turner · Accepted Answer · 2017-09-08 11:20:28Z

8

Personally, I'd use regex:

boolean valid = string.matches("[A-Za-z0-9]{5,}");

But if you're going to use streams, I'd do it like this:

boolean valid =
    s.length() >= 5 &&
    s.chars().allMatch(Character::isLetterOrDigit);

Noting that Character.isLetterOrDigit may match more characters than you want (e.g. १२३). You could additionally check that c < 128.

edited Sep 8, 2017 at 11:20

answered Sep 8, 2017 at 11:14

Andy Turner

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2 Comments

Sujal Mandal Over a year ago

smart solution !

prasad_ Over a year ago

Both the solutions answer my question. The first is precise and compact (and more efficient as you had mentioned) and the second is easily readable and maintainable. Thanks for replying.

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