We have defined our plugin in the project source directory, but we cannot re-use it in another project. We will learn how we can distribute our plugin logic, using a standalone project. Also, we will see how we can use the plugin in other projects.

By placing the plugin code in the buildSrc directory, we have separated the definition of the plugin and the usage. The plugin still cannot be used by other projects. To make the plugin reusable, we create a standalone project and create an artifact with the plugin code and publish the artifact to a repository. Other projects can then get the plugin from the repository and use the build logic from the plugin in the project.

We already have the code for the plugin and the test code in the buildSrc directory (from the previous section). We can copy this code to a new directory with the project for the plugin. In this new directory, we must also create a build.gradle file. The implicit dependencies and plugin added to a project in the buildSrc directory must be made explicit in a standalone project.

Let's create a new Gradle project in the directory plugin, and create the file build.gradle with the following content:

apply plugin: 'groovy'
apply plugin: 'maven'
version = 1.0
group = 'sample.infoplugin'
archivesBaseName = 'infoplugin'
repositories.mavenCentral()
dependencies {
    compile gradleApi()
    groovy localGroovy()
    testCompile group: 'junit', name: 'junit', version: '4.10'
}

uploadArchives {
    repositories.mavenDeployer {
        repository(url: 'file:../lib')
    }
}

Next, we create the plugin/src/main/groovy/sample and plugin/src/test/groovy/sample directories. We copy the InfoPlugin.groovy and InfoPluginExtension.groovy files to the src/main/groovy/sample directory, and the InfoPluginTest.groovy file to the plugin/src/test/groovy/sample directory.

So far we have all the ingredients to create an artifact JAR file with the plugin code. The artifact is deployed to the local ../lib directory. We can, of course, define any Maven or Ivy repository to deploy the plugin artifact into.

To make sure Gradle can find the plugin, we must provide a properties file in the plugin/src/main/resources/META-INF/gradle-plugins directory with the name of our plugin. The properties file has a property key implementation-class with the full class name of the Plugin class.

We want to name our plugin as info, so in the plugin/src/main/resources/META-INF/gradle-plugins directory we create the info.properties file with the following code:

implementation-class = sample.InfoPlugin

We are ready to create the artifact with the plugin and upload it to our repository. We invoke the uploadArchives task, and we get the following output:

$ gradle uploadArchives
:compileJava UP-TO-DATE
:compileGroovy UP-TO-DATE
:processResources
:classes
:jar
:uploadArchives
Uploading: sample/infoplugin/infoplugin/1.0/infoplugin-1.0.jar to repository remote at file:../lib
Transferring 8K from remote
Uploaded 8K

BUILD SUCCESSFUL

Total time: 3.076 secs

The plugin is now in the repository. To use the plugin, we must create a new Gradle project. We must extend the classpath of this new project, and include the plugin as a dependency. We use the buildscript{} script block, where we can configure the repository location and a classpath dependency. For our sample we reference the local ../lib directory. In the dependencies section we set the classpath configuration to the InfoPlugin artifact.

The following sample build file contains the definitions:

buildscript {
    repositories {
        maven {
            url 'file:../lib'
        }
    }
    dependencies {
        classpath group: 'sample.infoplugin', name: 'infoplugin', version: '1.0'
    }
}

apply plugin: 'info'

info.prefix = 'Gradle version'

Our project now has the info task from the plugin. We can configure the plugin extension through the info object or the configuration closure.

If we run the info task, we get the following output:

$ gradle info
:info
Gradle version: 1.1

BUILD SUCCESSFUL

Total time: 3.073 secs