bean validation not working with kotlin (JSR 380)

Question

so first of all i could not think of a better title for this question so i\'m open for changes.

I am trying to validate a bean using the bean validation mechanism (JSR-3

Answer 1

Answer (Kotlin 1.3.70)

Make sure to compile the kotlin code with jvm target 1.8 or greater and enable this feature by providing the -Xemit-jvm-type-annotations when compiling.

For Spring Boot projects you only have to do the following changes (tested with Spring Boot 2.3.3 and Kotlin 1.4.0):

1. In your pom set the following property:

   
       11
       1.4.0
   
   

2. Add -Xemit-jvm-type-annotations to the kotlin-maven-plugin:

   
       
           kotlin-maven-plugin
           org.jetbrains.kotlin
           
               
                   -Xjsr305=strict
                   -Xemit-jvm-type-annotations
               
               
                   spring
               
           
           
               
                   org.jetbrains.kotlin
                   kotlin-maven-allopen
                   ${kotlin.version}
               
           
       
   
   

Sample Project

---

Workaround (pre Kotlin 1.3.70)

Rafal G. already pointed out that we could use a custom validator as a workaround. So here's some code:

The Annotation:

import javax.validation.Constraint
import javax.validation.Payload
import kotlin.annotation.AnnotationTarget.ANNOTATION_CLASS
import kotlin.annotation.AnnotationTarget.CONSTRUCTOR
import kotlin.annotation.AnnotationTarget.FIELD
import kotlin.annotation.AnnotationTarget.FUNCTION
import kotlin.annotation.AnnotationTarget.TYPE_PARAMETER
import kotlin.annotation.AnnotationTarget.VALUE_PARAMETER
import kotlin.reflect.KClass

@MustBeDocumented
@Constraint(validatedBy = [NoNullElementsValidator::class])
@Target(allowedTargets = [FUNCTION, FIELD, ANNOTATION_CLASS, CONSTRUCTOR, VALUE_PARAMETER, TYPE_PARAMETER])
@Retention(AnnotationRetention.RUNTIME)
annotation class NoNullElements(
    val message: String = "must not contain null elements",
    val groups: Array> = [],
    val payload: Array> = []
)

The ConstraintValidator:

import javax.validation.ConstraintValidator
import javax.validation.ConstraintValidatorContext

class NoNullElementsValidator : ConstraintValidator> {
    override fun isValid(value: Collection?, context: ConstraintValidatorContext): Boolean {
        // null values are valid
        if (value == null) {
            return true
        }
        return value.stream().noneMatch { it == null }
    }
}

And finally the updated User class:

data class User(
    @field:NotEmpty
    @field:NoNullElements
    var roles: MutableSet = HashSet()
)

---

Altough validation works now, the resulting ConstrainViolation is slightly different. For example the elementType and propertyPath differs as you can see below.

Java:

Kotlin:

Source is available here: https://github.com/DarkAtra/jsr380-kotlin-issue/tree/workaround

Thanks again for your help Rafal G.