Kotlin Spring Request Blank Validation Best Practice - spring

Question

I'm new to kotlin and so far I have 2 options to do not blank validation on incoming HTTP request since a blank string considered as valid value in kotlin null checking.
Validation on class init function
data class Foo(val key: String) {
init {if (this.key.isEmpty()) throw Exception("Invalid Request")}
}
Validation with javax annotation
data class Foo(#field.NotBlank val key: String)
Both ways are working as expected, I just curious on what's the best way to do this in kotlin. I'm afraid that my kotlin code is to java, at that point no use I work with kotlin

Answer 1

If you want to validate the incoming request, go for 2nd option.
Consider having more than one attribute, lets say you have class such as:
data class User(val name: String, val surname:String)
Then you have to write validation for each field. What if both name and surname are blank? The name validation throws an error, you add name to request and BAM, surname validation throws an error.
data class User(val name: String, val surname:String) {
init {
if (this.name.isEmpty()) throw Exception("Name is missing")
if (this.surname.isEmpty()) throw Exception("Surname is missing)
}
}
You can validate all at once, using OR for example, but then you would lose explicit error - what was wrong? Blank name? Blank surname? Both were blank...?
data class User(val name: String, val surname:String) {
init {
if (this.name.isEmpty() || this.surname.isEmpty()) throw Exception("Name or surname is missing")
}
}
Now think about three, four, five fields.
If you use javax.validation properly, you have to write just the annotations and the rest is done by the framework - it will explictly say, what is wrong, on which field, because it checks all the constraints and if there are any violations, it throws an error with all violation details.