kotlin program error: no main manifest attribute in jar file - kotlin

Question

I wrote a simple kotlin helloworld program
hello.kt
fun main(args: Array<String>) {
println("Hello, World!")
}
Then I compiled it with kotlinc
$kotlinc hello.kt -include-runtime -d hello.jar
there was no errors and hello.jar was generated.
when I ran it
$java -jar hello.jar
it said there is no main manifest attribute in hello.jar
$no main manifest attribute, in hello.jar
I couldn't figure out this problem.
My kotlin version is 1.3.40, JDK version is 1.8.0

Answer 1

I came accross this answer while having the same issue with Kotlin and gradle. I wanted to package to get the jar to work but kept on pilling errors.
With a file like com.example.helloworld.kt containing your code:
fun main(args: Array<String>) {
println("Hello, World!")
}
So here is what the file build.gradle.kts would look like to get you started with gradle.
import org.gradle.kotlin.dsl.*
import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
plugins {
application
kotlin("jvm") version "1.3.50"
}
// Notice the "Kt" in the end, meaning the main is not in the class
application.mainClassName = "com.example.MainKt"
dependencies {
compile(kotlin("stdlib-jdk8"))
}
tasks.withType<KotlinCompile> {
kotlinOptions.jvmTarget = "1.8"
}
tasks.withType<Jar> {
// Otherwise you'll get a "No main manifest attribute" error
manifest {
attributes["Main-Class"] = "com.example.MainKt"
}
// To avoid the duplicate handling strategy error
duplicatesStrategy = DuplicatesStrategy.EXCLUDE
// To add all of the dependencies otherwise a "NoClassDefFoundError" error
from(sourceSets.main.get().output)
dependsOn(configurations.runtimeClasspath)
from({
configurations.runtimeClasspath.get().filter { it.name.endsWith("jar") }.map { zipTree(it) }
})
}
So once you gradle clean build you can either do:
gradle run
> Hello, World!
Assuming your projector using the jar in build/libs/hello.jar assuming that in your settings.gradle.kts you have set rootProject.name = "hello"
Then you can run:
java -jar hello.jar
> Hello, World!

Answer 2

Try to upgrade to version 1.3.41 and using JDK 1.11+.