[FIXED] Kotlin Spring Boot bean validation not working

Issue

I have quite a few projects that is slowly being migrated from Java to Kotlin, but I'm facing a problem when changing from Java POJO to Kotlin data classes. Bean validation stops working in REST controllers. I have created a very simple project directly from https://start.spring.io to demonstrate the failure.

@SpringBootApplication
class RestValidationApplication

fun main(args: Array<String>) {
    runApplication<RestValidationApplication>(*args)
}

@RestController
class Controller {

    @PostMapping
    fun test(@Valid @RequestBody request: Test) {
        println(request)
    }
}

data class Test(@field:NotNull val id: String)

and gradle:

import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
    id("org.springframework.boot") version "2.6.1"
    id("io.spring.dependency-management") version "1.0.11.RELEASE"
    kotlin("jvm") version "1.6.0"
    kotlin("plugin.spring") version "1.6.0"
}

group = "com.example"
version = "0.0.1-SNAPSHOT"
java.sourceCompatibility = JavaVersion.VERSION_17

repositories {
    mavenCentral()
}

dependencies {
    implementation("org.springframework.boot:spring-boot-starter-validation")
    implementation("org.springframework.boot:spring-boot-starter-web")
    implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
    implementation("org.jetbrains.kotlin:kotlin-reflect")
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
    testImplementation("org.springframework.boot:spring-boot-starter-test")
}

tasks.withType<KotlinCompile> {
    kotlinOptions {
        freeCompilerArgs = listOf("-Xjsr305=strict")
        jvmTarget = "17"
    }
} 

Sending a request does not trigger the bean validation, but it throws a HttpMessageNotReadableException because id is NULL.

curl -X POST http://localhost:8080 -H "Content-Type: application/json" -d "{}"

I have tried both @Valid and @Validated and using @get:NotNull on the attributes, but nothing works. I see many others have the same problem and using a Java class from a Kotlin REST controller works. Also changing to a non data class makes validation works. Anyone know if it's possible to get bean validation working with Kotlin data classes?

Solution

The issue has been fixed in Kotlin version 1.6.10. https://github.com/JetBrains/kotlin/releases/tag/v1.6.10. After upgrading the exception is now org.springframework.web.bind.MethodArgumentNotValidException.

Answered By - Jonas Pedersen