Configuring Gradle with Kotlin

Question

I am trying to use kotlin with gradle, but I am unable to succesfully create a project with Intellij Idea 15.

I've create simple project with two modules hello-java and hello-kotlin.

hello-java is plain java project and it is compiling and running perfectly fine.

hello-kotlin is simple kotin module, with just one *.kt file and build.gradle file.
Here are the sources:

build.gradle

group 'pl.fzymek.kotlin'
version '1.0-SNAPSHOT'

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:0.10.4"
    }
}

apply plugin: 'kotlin'
apply plugin: 'application'

mainClassName = 'HelloKotlinKt'

repositories {
    mavenCentral()
}

jar {
    manifest {
        attributes 'Main-Class': mainClassName
    }
}

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib:0.10.4"
}

HelloKotlin.kt

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

main module settings.gradle

include 'hello-java'
include 'hello-kotlin'

When running gradlew clean build all projects are compiled successfully, but when running java -jar hello-kotlin-1.0-SNAPSHOT.jar I get following error:

Exception in thread "main" java.lang.NoClassDefFoundError: kotlin/jvm/internal/Intrinsics
        at HelloKotlinKt.main(HelloKotlin.kt)
Caused by: java.lang.ClassNotFoundException: kotlin.jvm.internal.Intrinsics
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 1 more

What is more, Intellij seems not to recognize src/main/kotlin directory as source directory (it's not marked in blue) and I am not able to use auto-complete feature when editing HelloKotlin.kt file.

Here's my project structure in Intellij project window

I've tried using Intellij option to configure modules with Kotlin(Tools->Kotlin->Configure project with Kotlin), but it gives me error that "All modules with kotlin files are configured"

Help me stackoverflow, you are my only help.

Answer 1

When running gradlew clean build all projects are compiled successfully, but when running java -jar hello-kotlin-1.0-SNAPSHOT.jar I get following error...

jar {
    manifest {
        attributes 'Main-Class': 'HelloKotlinKt'
    }

    from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } }
}

What is more, Intellij seems not to recognize src/main/kotlin directory as source directory (it's not marked in blue)...

sourceSets {
    main.java.srcDirs += 'src/main/kotlin'
}

Documentation and useful resources can be found here and there.

Answer 2

Why doesn't my application run?

The Jar you're creating doesn't include the kotlin runtime as Gradle will only build a Jar with your class files in it. I see you're using the application plugin so either doing $ gradle run or creating a distribution and executing through the provided shell script should work ok. If you want to ship kotlin with your Jar you'll need to create a fat jar.

Why doesn't IDEA recognise the source directory?

I suspect this is down to the fact you haven't applied the idea plugin in your build file. I haven't done any work with Kotlin, but with other languages this is required to set up the workspace correctly.