使用Java 8流API的字符串长度和字符验证

Question

Find if an input String is valid - the criteria is String length greater than 5 and characters must be az, AZ 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);

Answer 1

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 (eg १२३ ). You could additionally check that c < 128 .