ClassNotFoundException when running jar file #187

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

application {
    mainClassName = "MainKt"
}

plugins {
    kotlin("jvm") version "1.4.0"
    application
}
group = "testinpubsublib"
version = "0.9.0"

repositories {
    mavenCentral()
    jcenter()
}
dependencies {
    implementation(platform("com.google.cloud:libraries-bom:20.4.0"))
    implementation("com.google.cloud:google-cloud-pubsub")
}

tasks.jar {
    // names the jar app.jar
    archiveFileName.set("gcppubsubtest.jar")
    manifest {
        // helps make the jar executable by telling where the entry method is
        attributes["Main-Class"] = "MainKt"
    }

    // adds all deps into the jar making it a "fat jar", runable on its own
    from { configurations.runtimeClasspath.get().map { if (it.isDirectory) it else zipTree(it) } }
}

tasks.withType<KotlinCompile>() {
    kotlinOptions.jvmTarget = "14"
}

fun main(args: Array<String>) {
    println("Hello World!")
}

# first download all deps, allows for faster builds when only our code changed
FROM gradle:6.6-jdk14 as cacheRUN mkdir -p /home/gradle/cache_home
ENV GRADLE_USER_HOME /home/gradle/cache_home
COPY build.gradle.kts /home/gradle/kotlin-code/
WORKDIR /home/gradle/kotlin-code
RUN gradle clean build -i --stacktrace
# copy in the deps from the above image, and now pull in the code and build that, creating an executable fat jar
FROM gradle:6.6-jdk14 as builder
COPY --from=cache /home/gradle/cache_home /home/gradle/.gradle
COPY . /usr/src/kotlin-code/
WORKDIR /usr/src/kotlin-code
RUN gradle build -i --stacktrace
RUN ls /usr/src/kotlin-code /usr/src/kotlin-code/build/libs
# Slimmed down running env where we only copy in the jar. This is what actually would be run in prod.
FROM openjdk:14-jdk-alpine
COPY --from=builder /usr/src/kotlin-code/build/libs/gcppubsubtest.jar /bin/runner/run.jar
WORKDIR /bin/runner
CMD ["java","-jar","run.jar"]