Hi all - New to gradle. I’m sure I’m doing something silly, but I’m trying to add a jar building cap...

# gradle

[Muhammad Talha]

Hi all - New to gradle. I’m sure I’m doing something silly, but I’m trying to add a jar building capability to my gradle file. But I’m getting an error: Expression 'jar' cannot be invoked as a function. The function 'invoke()' is not found . I already added the java plugin in the plugins function. Would any one be able to provide some guidance? Thanks!

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

plugins {
    kotlin("jvm") version "1.6.21"
    java
    application
}

group = "me.talha"
version = "1.0-SNAPSHOT"

repositories {
    mavenCentral()
}

dependencies {
    testImplementation(kotlin("test"))
}

tasks.test {
    useJUnitPlatform()
}

tasks.withType<KotlinCompile>() {
    kotlinOptions.jvmTarget = "11"
}

application {
    mainClass.set("MainKt")
}

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

[Vampire]

You are trying to configure a task named "jar", so use tasks.jar { ... }.
There is no extension registered that is called "jar".
Just doing without tasks. is syntactic sugar only available in Groovy DSL, not in Kotlin DSL.

But actually, I'd recommend you don't set the main class attribute on the jar and worse probably try to build a fat jar.
You already applied and configured the "application" plugin, so use it, it builds a proper distribution with all dependencies, your code, additional files you probably configured and generated start scripts with which you can easily start your application. Just use the distZip or distTar task to generate a distributable archive of the respective type, or `assemble`and thus also build to create them both.

[Muhammad Talha]

Thanks, @Vampire - Seems like it might be appropriate at some point for me to take a step back and understand Gradle better. Trial and error only seems to be getting me so far. Your tips helped a lot. I see the generated zip file after using the distZip command. However when I run the jar i get a no main manifest attribute, in copycurrbranchkt-1.0-SNAPSHOT.jar error. Any idea why that might be? Is there a way in Gradle to also generate a manifest attribute?

[Muhammad Talha]

Hmm or maybe I’m misunderstanding how to run it. The executable in the bin folder works fine and I’m guessing uses the jar

[ephemient]

Gradle generates start scripts that are also in the distribution, bin folder as you have found

[ephemient]

it sets up the classpath for your jar and all its runtime dependencies

[Muhammad Talha]

Okay that’s awesome - thanks!

[Muhammad Talha]

Out of curiosity, the generated jar(s) alone should work fine in any projects I want to use it in right?

[Vampire]

You can even configure where the start scripts are generated.
I personally like them to be at the root directory of the distribution

[Vampire]

Out of curiosity, the generated jar(s) alone should work fine in any projects I want to use it in right?

Heavily depends on what you mean with that

[Vampire]

It is just a jar with your code compiled in it

[Vampire]

So yes, you can use it as library too if that is intended

[ephemient]

the jar does not carry its dependencies with it. if you want to share it between projects, you would best use a Maven repository, which can carry additional metadata, or other tools like Gradle's includeBuild

[ephemient]

(but if your jar is meant to be a library, it seems a bit unusual to apply the application plugin?)

[Muhammad Talha]

Probably, I actually don’t know much about what’s in here yet 😅

[Muhammad Talha]

Thanks for the help! I think it’s worth for me to learn some Gradle basics.

[Vampire]

Always 🙂