Custom Spring annotation and validator in Kotlin

Validators.kt

package io.license.core.validation

import javax.validation.Constraint
import javax.validation.ConstraintValidator
import javax.validation.ConstraintValidatorContext
import javax.validation.Payload
import kotlin.reflect.KClass


@Target(AnnotationTarget.FIELD)
@MustBeDocumented
@Constraint(validatedBy = [NullableNotBlankValidator::class])
annotation class NullableNotBlank(
        val message: String = "{javax.validation.constraints.NotBlank.message}",
        val groups: Array<KClass<*>> = [],
        val payload: Array<KClass<out Payload>> = []
)

class NullableNotBlankValidator : ConstraintValidator<NullableNotBlank, String> {
    override fun isValid(value: String?, context: ConstraintValidatorContext?): Boolean {
        if (value == null) return true
        return value.isNotBlank()
    }
}

Hi @vbsteven,

thanks for sharing your Validator and Annotation.

I changed the isValid Method in NullableNotBlankValidator a bit.

class NullableNotBlankValidator : ConstraintValidator<NullableNotBlank, String> {
    override fun isValid(value: String?, context: ConstraintValidatorContext?) = value?.isNotBlank() ?: true
}

The related tests stay successful

package io.license.core.validation

import org.junit.jupiter.api.Assertions.assertFalse
import org.junit.jupiter.api.Assertions.assertTrue
import org.junit.jupiter.api.Test
import org.junit.jupiter.params.ParameterizedTest
import org.junit.jupiter.params.provider.ValueSource

internal class NullableNotBlankValidatorTest {

    private val validator = NullableNotBlankValidator()

    @Test
    fun `should find no validation error, if value is null`() {
        assertTrue(validator.isValid(value = null, context = null))
    }

    @Test
    fun `should return validation error, if value is empty`() {
        assertFalse(validator.isValid(value = "", context = null))
    }

    @ParameterizedTest
    @ValueSource(strings = [" ", "  ", "   "])
    fun `should return validation error, if value contains only spaces`(value: String) {
        assertFalse(validator.isValid(value = value, context = null))
    }

    @ParameterizedTest
    @ValueSource(strings = ["a", " a", "a ", " a "])
    fun `should find no validation error, if value contains at least one character`(value: String) {
        assertTrue(validator.isValid(value = value, context = null))
    }
}

Thanks for sharing this Kotlin gist. They are hard to come by and deeply appreciated.