spring testutils beanValidation (Kotlin) - How to construct a LocalValidatorFactoryBean (extends org.springframework.validation.Validator)

beanValidationTestUtils.kt

package com.example.testutils.beanvalidation

import org.hibernate.validator.HibernateValidator
import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean

fun localValidatorFactoryBean():LocalValidatorFactoryBean {
    val validator= LocalValidatorFactoryBean()
    validator.setProviderClass(HibernateValidator::class.java)
    validator.afterPropertiesSet()
    return validator
}

// Example
@RunWith(MockitoJUnitRunner::class)
class SomeRequestHandlerTest {

    private lateinit var handler: SomeRequestHandler
    private val validator: Validator = localValidatorFactoryBean()
    @Mock private lateinit var repoService: SomeRepoService

    @Before
    fun setup() {
        handler = SomeRequestHandler(repoService=repoService, validator=validator)
    }
 }
    

beanValidationUtils.kt

package com.example.api.common

import org.springframework.validation.DataBinder
import org.springframework.validation.Validator

@ResponseStatus(value = HttpStatus.BAD_REQUEST)
class BadRequestException(message: String) : RuntimeException(message)

fun <T : Any> validateBean(validator: Validator, value: T, beanName: String?): T {
    val binder = if (beanName == null) {
        DataBinder(value)
    } else {
        DataBinder(value, beanName)
    }
    binder.validator = validator
    binder.validate()
    val result = binder.bindingResult
    if (!result.hasErrors()) {
        return value
    }

    val errors = result.fieldErrors.map {
        mapOf<String, Any?>(
                "field" to "${it.objectName}.${it.field}",
                "message" to it.defaultMessage
        )
    }

    val classname: String = value::class.qualifiedName ?: value::class.toString()
    val msg = "Failed to validate bean=$classname objectName: ${result.objectName} nestedPath: ${result.nestedPath} allErrors:${errors.joinToString("\n")}"

    throw BadRequestException(msg)
}

// Example:

data class SomeRequest(
  @get:[Min(1) Max(100)] val limit: Int,
  @get:[Min(0) Max(1_000_000)] val offset: Int
)
@Component
class SomeHandler(private val validator:Validator) {
  fun handle(req:SomeRequest):SomeResponse =
    req
      .let { validateBean(validator = validator, value = it, beanName = "request") }
      .let { getSomeDataFromDb(it)}
      .let { mapToResponse(it) }

  private fun getSomeDataFromDb(req:SomeRequest):SomeDataFromDb
  private fun mapToResponse(dataFromDb:SomeDataFromDb):SomeResponse
}