Upload your library

To grant access to your library, you need to choose a repository. This page guides you through the considerations related to choosing a repository type and shows how to create a publication using the Maven Publish Plugin.

Before uploading your library, make sure you have prepared your library for release and configured any necessary publication variants or test fixtures.

Choose a repository type

Libraries are published as AAR files. These files contain compiled code as bytecode and native libraries, an Android manifest, and resources. The package itself does not declare any identity, version, or dependencies on other libraries.

Providing AARs through a repository is generally the best practice, rather than distributing the AAR directly. It helps users have a better understanding of where the library is coming from rather than having to deal with a name.aar file without important details, like version. When upgrading to a newer version of a library, use a repository to ensure that only the required dependencies of the newer version are added, so that users don't have to manually update dependencies.

There are multiple benefits to using a repository to publish your library:

• Gradle can automatically add your library’s dependencies to the dependency graph.
• Gradle can ensure that a single version of your library is in the dependency graph, resolving conflicts if your library is transitively included more than once with different versions.
• The Android Gradle Plugin (AGP) can do more efficient desugaring if your library uses Java 8 or higher language features, reducing build times for your users.
• Your library can use variant publishing and include features like test fixtures.

Distributing the AAR directly doesn't provide your user with any information regarding the identity, version, or dependencies of your library. When publishing to a repository, distribution is handled by a separate file that is part of the repository mechanism. For Maven repositories, this is the POM file. Therefore, it is strongly recommended to publish libraries using repositories rather than manually distributing AAR files.

Types of repositories

There are three types of repositories:

• Free online repositories, like Maven Central, let anyone upload and download libraries.
• Private repositories, with access via login, allow controlled distribution of private libraries.
• Local, folder-based repositories allow distribution of libraries through manual download.

Using local, folder-based repositories is very similar to providing your users with a manual download link to the AAR or sending the AAR by email. The main difference is that you are not sending just the AAR but also the additional information about identity, version, and dependencies.

You distribute a zip file of the folder-based repository containing your AAR plus the metadata. Your users can then extract the file's contents, add the contents to their project, and point Gradle to it. From then on, the users can declare a dependency on the library using Maven coordinates, as if the library were in an online repository, and benefit from all the advantages mentioned earlier.

Create the publication

Publish using the Gradle Maven Publish Plugin. The Maven Publish Plugin lets you declare publications and repositories and creates tasks to publish these publications to the repositories. These publications consume a SoftwareComponent instance that the plugin that drives the build creates, which could be AGP or the java-library plugin.

Note that when running the Maven Publish Plugin with AGP, the software components are not created directly when the plugin is applied. They are instead created during the afterEvaluate() callback step. Therefore, the publication that selects the software component must also be configured during the afterEvaluate() step.

The following code snippet of the module-level build.gradle file creates a publication for a given variant created with singleVariant() or multipleVariants():

publishing {
  publications {
    release(MavenPublication) {
      groupId = 'com.my-company'
      artifactId = 'my-library'
      version = '1.0'

      afterEvaluate {
        from components.release
      }
    }
  }
}

publishing {
  publications {
    register<MavenPublication>("release") {
      groupId = "com.my-company"
      artifactId = "my-library"
      version = "1.0"

      afterEvaluate {
        from(components["release"])
      }
    }
  }
}

In the preceding example, the name of the component (components.release) is based on the name that was given to either singleVariant() or multipleVariants().

Once you declare a publication, you must create a target repository.

Publish to a local repository

Publishing to a local repository is very similar to publishing to a remote repository, except for the repository declaration. Read the preceding section to learn how to publish to a remote repository to create a publication that publishes the desired variant or variants. Then create a local repository:

publishing {
  publications {
    release(MavenPublication) {
      ...
    }
  }
  repositories {
    maven {
      name = 'myrepo'
      url = layout.buildDirectory.dir("repo")
    }
  }
}

publishing {
  publications {
    register<MavenPublication>("release") {
      ...
    }
  }
  repositories {
    maven {
      name = "myrepo"
      url = uri(layout.buildDirectory.dir("repo"))
    }
  }
}

This creates a task called publishReleaseToMyRepoRepository that consists of the name of the publication and the name of the repository. Run this task to generate the repository to the location provided. In this example, the repository is generated inside the build folder of the project, under a repo directory.

If you want to automatically generate a zip file of the repository, do so using the following code:

tasks.register('generateRepo', Zip) {
  def publishTask = tasks.named('publishReleasePublicationToMyrepoRepository')
  from publishTask.map { it.getRepository().getUrl() }
  into 'mylibrary'
  archiveFileName.set('mylibrary.zip')
}

tasks.register<Zip>("generateRepo") {
  val publishTask = tasks.named(
    "publishReleasePublicationToMyrepoRepository",
    PublishToMavenRepository::class.java)
  from(publishTask.map { it.repository.url })
  into("mylibrary")
  archiveFileName.set("mylibrary.zip")
}

This code creates a Zip task called generateRepo that consumes the content of the publishing task and compresses it while ensuring that the zip entries are in a top-level folder called mylibrary. The output is located under build/distributions.