Hello! I'm working on a compose multiplatform project that has a ktor server module, but I can't see...

# ktor

[Jonathan Morabito]

Hello! I'm working on a compose multiplatform project that has a ktor server module, but I can't seem to align JVM versions correctly.
Using JDK 20 to run Gradle, but I wish to target JDK 11 and run in docker.
🧵 ...

[Jonathan Morabito]

My build.gradle.kts:

import org.jetbrains.kotlin.gradle.dsl.JvmTarget

plugins {
    alias(libs.plugins.kotlinJvm)
    alias(libs.plugins.ktor)
    application
}

group = "com.example"
version = "1.0.0"

java {
    sourceCompatibility = JavaVersion.VERSION_11
    targetCompatibility = JavaVersion.VERSION_11
}

kotlin {
    compilerOptions.jvmTarget.set(JvmTarget.JVM_11)
}

ktor {
    docker.jreVersion.set(JavaVersion.VERSION_11)
}

application {
    mainClass.set("com.example.ApplicationKt")
    applicationDefaultJvmArgs = listOf("-Dio.ktor.development=${extra["development"] ?: "false"}")
}

dependencies {
    implementation(projects.shared)
    implementation(libs.logback)
    implementation(libs.ktor.server.core)
    implementation(libs.ktor.server.netty)
    testImplementation(libs.ktor.server.tests)
    testImplementation(libs.kotlin.test.junit)
}

[Jonathan Morabito]

and still somehow, when running:
./gradlew runDocker

It starts, but the first request leads to:

java.lang.UnsupportedClassVersionError: Greeting has been compiled by a more recent version of the Java Runtime (class file version 64.0), this version of the Java Runtime only recognizes class file versions up to 55.0

[Jonathan Morabito]

Are the options i set correct? And are there any I missed?

[Aleksei Tirman [JB]]

Can you try setting the JVM toolchain version?

kotlin {
    jvmToolchain(11)
}

[Jonathan Morabito]

I was hoping to use my local JDK, but target 11, rather than using a toolchain

[Aleksei Tirman [JB]]

This option sets the exact version of the Java language that the toolchain is required to support.

[Jonathan Morabito]

oh interesting. i thought it would try to download a new JDK altogether

[Jonathan Morabito]

trying this now. thanks!