Building a self-executable jar with Gradle and Kotlin

Question

I've written a simple kotlin source file in order to get started, and a gradle script file. But I can't figure out how to add the main func to the manifest, so that the jar could be self-executable.

Here my build.gradle script :

buildscript {     repositories {         mavenCentral()     }     dependencies {         classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:0.9.66'     } } apply plugin: "kotlin" repositories {     mavenCentral() } dependencies {     compile 'org.jetbrains.kotlin:kotlin-stdlib:0.9.66' }  jar {     manifest {         attributes 'Main-Class': 'com.loloof64.kotlin.exps.ExpsPackage'     } } 

Here is my com.loloof64.kotlin.exps.Multideclarations.kt

package com.loloof64.kotlin.exps  class Person(val firstName: String, val lastName: String) {     fun component1(): String {         return firstName     }     fun component2(): String {         return lastName     } }  fun main(args: Array < String > ) {     val(first, last) = Person("Laurent", "Bernabé")     println("First name : $first - Last name : $last") } 

When I launch the jar from terminal (java -jar MYJar.jar) I get the following stacktrace, saying me that the kotlin reflection library classes are missing, and indeed they have not been added to the jar. It seems that I am missing the kotlin-compiler artifact classes from the final jar, and also the kotlin-stdlib sources, but I don't know how to adapt the gradle build.

$> java -jar build/libs/kotlin_exps.jar   Exception in thread "main" java.lang.NoClassDefFoundError: kotlin/reflect/jvm/internal/InternalPackage     at com.loloof64.kotlin.exps.ExpsPackage.<clinit>(MultiDeclarations.kt) Caused by: java.lang.ClassNotFoundException: kotlin.reflect.jvm.internal.InternalPackage     at java.net.URLClassLoader$1.run(URLClassLoader.java:372)     at java.net.URLClassLoader$1.run(URLClassLoader.java:361)     at java.security.AccessController.doPrivileged(Native Method)     at java.net.URLClassLoader.findClass(URLClassLoader.java:360)     at java.lang.ClassLoader.loadClass(ClassLoader.java:424)     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)     at java.lang.ClassLoader.loadClass(ClassLoader.java:357)     ... 1 more 

I am using Kotlin 0.9.66 and gradle 2.1

Answer 1

Add the plugin application, then set the mainClassName as

mainClassName = '[your_namespace].[your_arctifact]Kt' 

For instance, suppose you have placed the following code in a file named main.kt:

package net.mydomain.kotlinlearn  import kotlin import java.util.ArrayList  fun main(args: Array<String>) {      println("Hello!")  } 

your build.gradle should be:

apply plugin: 'kotlin' apply plugin: 'application'  mainClassName = "net.mydomain.kotlinlearn.MainKt" 

In fact Kotlin is building a class to encapsulate your main function named with the same name of your file - with Title Case.