Gradle Skeleton

This is a skeleton project demonstrating the following:

• Multi-project Gradle configuration (project dependencies, alternative configurations).
• Sharing of common build logic using script plugins.
• Delegation of dependency management (including plugins and Gradle itself) to a private repository.
• Minimizing repetition of configuration boilerplate at the settings and project level.
• Using Kotlin to test Java projects. (Specifically, JUnit, Spek and Kluent.)

See *.gradle for specifics and discussion or below for more about setup and background.

Artifactory Setup

This example assumes you want to use a private repository server for all remote dependencies of the build. A private server has several advantages:

• It increases the likelihood that your build will work consistently even if upstream providers are down or slow.
• You have the flexibility to selectively deploy edge or override releases to problematic dependencies without losing the convenience of Gradle-style dependency declaration.
• Larger organizations may use a private repository for license monitoring or security purposes.

Using a private repository with Gradle can be challenging because there are multiple ways that Gradle tries to resolve build components. In addition to basic dependencies, there are also plugin dependencies and Gradle itself. All can be delegated, but the configuration to do so varies which is what this example tries to unify.

Artifactory is a popular repository server choice. It's easy to run and has an open-source version. These instructions assume that Artifactory has been setup with:

• A gradle-distributions generic remote repository backed by https://services.gradle.org/distributions/.
• A gradle-plugins maven-format remote repository backed by https://plugins.gradle.org/m2/.
• A maven-format remote repository backed by an upstream provider such as jcenter or maven central.
• A libs-release maven-format virtual repository merging the plugin and main maven repositories.

Docker installation (one option of many):

docker pull docker.bintray.io/jfrog/artifactory-oss
docker volume create --name my-artifactory-data
docker run --restart=unless-stopped -d --name jfrog-artifactory-oss-latest -p 8085:8081 -v my-artifactory-data/:/var/opt/jfrog/artifactory docker.bintray.io/jfrog/artifactory-oss:latest

See config.gradle for further instructions on configuring repository details.

Common Build Configuration

In a multi-project build or just across multiple single-project builds you will likely find that there are configuration patterns that recur. This is particularly true when it comes to repository configuration, but there may also be dependencies, versions or task logic that it's redundant to keep declaring.

The absolute minimum for a multi-project build is a settings.gradle in the root and then a build.gradle for each subproject.

In this example, reused configuration is added in gradle/common and referenced in the project build files. There's nothing special about that location; it's just out of the way. Gradle's meta buildSrc project can be useful for reused snippets as well, but it's unnecessary in this case.

For multiple standalone projects wanting to share common configuration, it might be appropriate to maintain the common directory on its own and use a pegged external in the source control configuration to graft it into projects that need it.

Why?

Not all of these approaches may be ideal, but they represent natural impulses when dealing with repeated elements across similar builds, and discovering how to accomplish them with the tools Gradle provides can be challenging. Gradle continues to address pain points, and hopefully future versions will provide idiomatic solutions for these concerns.

Comparison

For comparison, a single project, public repository version of what this example tries to abstract might look like the following build.gradle.

buildscript {
	repositories {
		maven {
			url 'https://plugins.gradle.org/m2'
		}
	}
	dependencies {
		classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:1.2.41'
	}
}

plugins {
	id 'java'
	id 'org.jetbrains.kotlin.jvm' version '1.2.41'
}

repositories {
	jcenter()
}

dependencies {
	testCompile 'org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.2.41'
	testRuntime 'org.jetbrains.kotlin:kotlin-reflect:1.2.41'

	testCompile 'org.junit.jupiter:junit-jupiter-api:5.2.0'
	testCompile 'org.junit.jupiter:junit-jupiter-engine:5.2.0'

	testCompile('org.jetbrains.spek:spek-api:1.1.5') {
		exclude group: 'org.jetbrains.kotlin'
	}
	testRuntime('org.jetbrains.spek:spek-junit-platform-engine:1.1.5') {
		exclude group: 'org.junit.platform'
		exclude group: 'org.jetbrains.kotlin'
	}

	testCompile 'org.amshove.kluent:kluent:1.37'
}

compileTestKotlin {
	kotlinOptions {
		jvmTarget = '1.8'
	}
}

test {
	useJUnitPlatform()
}