[bv-dev] Container element validation for arrays

Guillaume Smet guillaume.smet at gmail.com
Wed Apr 19 06:28:05 EDT 2017


FWIW, the main issue with BV 1.1 compatibility is that BV 1.1 supports:
[Example 1]
@Size(min = 2)
private String[] array;

which was the way to write that the array should have a minimum length of 2
(and was perfectly valid if the @Size constraint does not have a TYPE_USE

If we consider TYPE_USE support for arrays, according to the JLS, it should
in fact be written:
[Example 2]
private String @Size(min = 2) [] array;

And the main compatibility issue is that the meaning of [Example 1] would
not be compatible with the BV 1.1 behavior: it should mean that the String
inside the array must have a minimum length of  2.

See the class I used as a playground here:


On Wed, Apr 19, 2017 at 10:27 AM, Gunnar Morling <gunnar at hibernate.org>

> Hi,
> Guillaume made an important observation concerning the validation of
> array elements. So far we envisioned to support this:
>     String @Email [] emails;
> That looks nice (provided that @Email supports TYPE_USE), only that
> it's getting semantics of type annotations for arrays wrong.
> As per the JLS [1], the @Email annotation here applies to the array
> type String[], not the component type String. This example from the
> JLS clarifies the intent:
>     @C int @A [] @B [] f;
>     "@A applies to the array type int[][], @B applies to its component
> type int[],
>     and @C applies to the element type int."
> So according to that, our example would have to be:
>     @Email String[] emails;
> But obviously this conflicts with the existing semantics of applying
> constraints to arrays (not their elements) in BV 1.1.
> So based on that, I don't see a good way for supporting container
> element constraints for arrays. Hence my suggestion is to not support
> them in the BV 2.0 spec (the validation of container elements of
> generic containers - List<@Email String> - is not affected). Specific
> implementations may explore ways around it (e.g. specifying the target
> via payload()) and we may revisit it in 2.1.
> Any thoughts?
> --Gunnar
> [1] https://docs.oracle.com/javase/specs/jls/se8/html/jls-9.html#jls-9.7.4
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