Validation of null against Regex

Question

I am trying to validate a String in Java to see if it matches the randomUUID format using the following regex

^[0-9A-F]{8}-[0-9A-F]{4}-[0-9A-F]{4}-[0-9A-F]{4}-[0-9A-F]{12}$

Now this works fine and picks up invalid strings and so on – however, if I pass a null String to the regex, it returns true, so when I perform validation on the Pattern annotation, no constraint violations are reported. Is this expected behaviour, since the String is null it is not performing any validation?

As a way around this, on the getter method that I have annotated with the Pattern annotation, I have used this

return id != null ? id : "null"

This works, however it seems a bit... hacky to me :)

Standard Java doesn't have `Pattern` annotation but only class. Are you using some frameworks? — Pshemo, Nov 08 '13 at 20:15
I imagine passing a null string would generate a NullPointerException. Can you add the code where you are actually applying the pattern? — matt forsythe, Nov 08 '13 at 20:17
I am using Hibernate annotations, as far as I know now when null is passed no regex check is performed so I assume that is what is going wrong with my code! — KingTravisG, Nov 08 '13 at 20:26

score 4 · Accepted Answer · edited May 23 '17 at 12:12

4

If you want to exclude nulls, use a 'not null' annotation, such as @NotNull.

PatternValidator returns true if the argument is null (a weird choice, IMHO); it says so right in the source. I've seen different versions, and they all did this, so it's really part of the contract (and should be documented better).

public boolean isValid(String value, ConstraintValidatorContext constraintValidatorContext) {
    if ( value == null ) {
        return true;
    }
    Matcher m = pattern.matcher( value );
    return m.matches();
}

edited May 23 '17 at 12:12

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answered Nov 08 '13 at 20:30

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Yes, very strange, although I can understand how technically null does not equal the pattern... – KingTravisG Nov 14 '13 at 09:21

Validation of null against Regex

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