Hi all, I have question regarding annotations. Ass...

# announcements

[Jaro]

Hi all, I have question regarding annotations. Assume a following example

open class A(val strings: List<String>)

class B(strings: List<String>) : A(strings)

class C(strings: List<String>) : A(strings)

these classes are used in my REST API and I would like to validate their content with JSR annotations. I want to check that the collection strings in class B is not empty using @NotEmpty but I can apply this validation only on the property declaration (if I’m not mistaken). What is the best Kotlin way to add this validation to class B ? In java I would probably override getter in class B and add annotation there, can I do something similar in Kotlin?

[Jukka Siivonen]

Sorry not to answer your question, but looking back my non-trivial Kotlin project using JSR annotations I would not use them at all. I think Kotlin provides far better options in this area

[Jaro]

No problem with not answering the question. We are using JSR quite some time and it is not feasible to change it… I’m just new to kotlin and I do not know how to handle this problem in kotlin idiomatic way.

[thanksforallthefish]

you can change class B(strings: List<String>) : A(strings) to class B(@get:NotEmpty override val strings: List<String>) : A(strings)

[thanksforallthefish]

provided you also have open class A(open val strings: List<String>)

[Jaro]

I have tough that this the way how to solve the problem, but somehow I do not like to override the property to just have this annotation.

[Jaro]

but looks like I do not have any other option. Thank you for you help.

[ahmad]

Sorry for interrupting the thread, but @Jukka Siivonen can you please elaborate more why don’t like JSR annotations with kotlin?

[Jukka Siivonen]

Mostly because I think validation should not be hardcoded in types and also like I said "external" validation with Kotlin should be very clean, for example https://www.konform.io/

[Jukka Siivonen]

for trivial validation JSR works fine, but we have cases when validation needs to be different depending on object state / external state etc. and using validation groups gets really messy. Maybe better domain modeling would help with this, but I would still prefer external validation

[ahmad]

Thanks a lot for the explanation

[thanksforallthefish]

jsr is not the best api I ever saw, but it is actually super-convenient once you really know how it works. While I would like more a dsl api rather than an annotation api, being a standard it means it integrates awesomely with a lot of tooling to help with the non-functional requirement of validation.

for instance, hibernate-validator recently added a feature to automatically transform the error path, so if you are receive a json request and validating the request, you can easily return a response where you indicate the json name of the field violating the rules, rather than the kotlin/java you would get natively