I have a bunch of bean properties that I need to be in a specific format, but only if they are non-null. This will be a common pattern. If I use @Size with min/max, or @Digits, they will fail if the value is null.

What's are some reasonable strategies for facilitating this? I don't want to implement a custom validator for every property, although I could perhaps live with a single validator and annotation like "@OnlyValidateIfNotNull", if it were possible for that to work.

Hmm. I guess this is a longstanding issue: https://stackoverflow.com/questions/175 ... s-not-null .

So if I were to implement a "@NullOrSize" validator (and something similar for "Digits" and others), is there anything I can reuse? I see that the "@Size" validator is built-in ("validatedBy" empty). The implementation would be straightforward, but I'd prefer not to write code that I don't have to.

Hmm, maybe I should say never mind about the whole issue. It does appear that "@Size" with a min value doesn't fail if the value is null.

All the built-in constraints accept null as a valid input (except @NotNull of course), so no custom constraints are needed for that. The idea is that @NotNull should be explicitly added if null is not a valid value.