Using Kotlin with Gradle

Question

Using Kotlin with Gradle

I am new to Kotlin

and Gradle

and tried these steps, so I got the following 2 files

after running, gradle init

I changed build.gradle

as follows:

// set up the kotlin-gradle plugin
buildscript {
    ext.kotlin_version = '1.1.2-2'

    repositories {
        mavenCentral()
    }

    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

// apply the kotlin-gradle plugin
apply plugin: "kotlin"
apply plugin: 'application'

mainClassName = "hello.main"

// add kotlin-stdlib dependencies.
repositories {
    mavenCentral()
}

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

Hello.kt

:

package hello   

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

Then I ran gradle build

and gotbuild\classes\main\hello\HelloKt.class

my question is why the file is .class

not generated .jar

and how to get the file .jar

and how to run it, i tried to run the generated file with kotlin -classpath HelloKt.class main

but got the errorerror: could not find or load main class hello.main

+3

java kotlin gradle

Hasan a yousef May 31 '17 at 16:46

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2 answers

Classes are direct output from the Kotlin compiler and must be packaged in JARs using Gradle afterwards. To create a JAR, you can run a task jar

just like in a Java project:

gradle jar

^{This task usually runs on time gradle build

due to task dependencies.}

This will package the Kotlin classes into a JAR archive (along with other JVM classes if you have a multilingual project), usually found in .build/libs/yourProjectName.jar

Regarding running the JAR, see this Q&A for a detailed explanation: (link)

+2

hotkey May 31 '17 at 16:54

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Hasan a yousef · Accepted Answer · 2017-05-31T20:18:53+0000

Thanks for @ hotkey's answer, it got me going the right way.

First of all, there is a mistake in the declaration of the main class, as it must follow the new methodology, which is in the following format:

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

namespace = package name

arctifact = filename

so given the names given in the example above, where filename is: Hello.kt

and the namespace hello

is then:

mainClassName = `[hello].[Hello]Kt`

using the previous method which contains:

apply plugin: 'application'
mainClassName = 'hello.HelloKt'

the generated .jar file does not include the kotlin runtime, so the only way to execute it is:

d:/App/build/libs/kotlin -cp App.jar hello.HelloKt

but to create a standalone jar

that can run on its own, and contains kotlin runtime

, then build.gradle

must be written as:

// set up the kotlin-gradle plugin
buildscript {
    ext.kotlin_version = '1.1.2-2'

    repositories {
        mavenCentral()
    }

    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

// apply the kotlin-gradle plugin
apply plugin: "kotlin"


// add kotlin-stdlib dependencies.
repositories {
    mavenCentral()
}

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

jar {
    manifest {
        //Define mainClassName as: '[your_namespace].[your_arctifact]Kt'
        attributes 'Main-Class': 'hello.HelloKt'
    }

    // NEW LINE HERE !!!
    from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } }
}

followed by a gradle build

file [your_working_folder].jar

will be generated in a folder build/libs

assuming the working folder name is application, then an app.jar file will be generated .

You can use one of the following two commands to run this file:

D:\App\build\libs\java -jar App.jar

OR

D:\App\build\libs\kotlin App.jar hello.HelloKt

Using Kotlin with Gradle

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