Chapter 66. Maven Publishing (new)

The ability to publish in the Maven format is provided by the “maven-publish” plugin.

The “publishing” plugin creates an extension on the project named “publishing” of type PublishingExtension. This extension provides a container of named publications and a container of named repositories. The “maven-publish” plugin works with MavenPublication publications and MavenArtifactRepository repositories.

apply plugin: 'maven-publish'

Applying the “maven-publish” plugin does the following:

Publication objects describe the structure/configuration of a publication to be created. Publications are published to repositories via tasks, and the configuration of the publication object determines exactly what is published. All of the publications of a project are defined in the PublishingExtension.getPublications() container. Each publication has a unique name within the project.

For the “maven-publish” plugin to have any effect, a MavenPublication must be added to the set of publications. This publication determines which artifacts are actually published as well as the details included in the associated POM file. A publication can be configured by adding components, customizing artifacts, and by modifying the generated POM file directly.

publications {
        mavenJava(MavenPublication) {
            from components.java
        }
    }

task sourceJar(type: Jar) {
    from sourceSets.main.allJava
}

publishing {
    publications {
        mavenJava(MavenPublication) {
            from components.java

            artifact sourceJar {
                classifier "sources"
            }
        }
    }
}

publishing {
        publications {
            maven(MavenPublication) {
                groupId 'org.gradle.sample'
                artifactId 'project1-sample'
                version '1.1'

                from components.java
            }
        }
    }

publications {
        mavenCustom(MavenPublication) {
            pom.withXml {
                asNode().appendNode('description',
                                    'A demonstration of maven POM customization')
            }
        }
    }

task apiJar(type: Jar) {
        baseName "publishing-api"
        from sourceSets.main.output
        exclude '**/impl/**'
    }

    publishing {
        publications {
            impl(MavenPublication) {
                groupId 'org.gradle.sample.impl'
                artifactId 'project2-impl'
                version '2.3'

                from components.java
            }
            api(MavenPublication) {
                groupId 'org.gradle.sample'
                artifactId 'project2-api'
                version '2'

                artifact apiJar
            }
        }
    }

Publications are published to repositories. The repositories to publish to are defined by the PublishingExtension.getRepositories() container.

repositories {
        maven {
            // change to point to your repo, e.g. http://my.org/repo
            url "$buildDir/repo"
        }
    }

The DSL used to declare repositories for publication is the same DSL that is used to declare repositories to consume dependencies from, RepositoryHandler. However, in the context of Maven publication only MavenArtifactRepository repositories can be used for publication.

The “maven-publish” plugin automatically creates a PublishToMavenRepository task for each MavenPublication and MavenArtifactRepository combination in the publishing.publications and publishing.repositories containers respectively.

The created task is named “publish«PUBNAME»PublicationTo«REPONAME»Repository”.

apply plugin: 'java'
apply plugin: 'maven-publish'

group = 'org.gradle.sample'
version = '1.0'

publishing {
    publications {
        mavenJava(MavenPublication) {
            from components.java
        }
    }
    repositories {
        maven {
            // change to point to your repo, e.g. http://my.org/repo
            url "$buildDir/repo"
        }
    }
}

> gradle publish
:generatePomFileForMavenJavaPublication
:compileJava
:processResources UP-TO-DATE
:classes
:jar
:publishMavenJavaPublicationToMavenRepository
:publish

BUILD SUCCESSFUL

Total time: 1 secs

In this example, a task named “publishMavenJavaPublicationToMavenRepository” is created, which is of type PublishToMavenRepository. This task is wired into the publish lifecycle task. Executing “gradle publish” builds the POM file and all of the artifacts to be published, and transfers them to the repository.

For integration with a local Maven installation, it is sometimes useful to publish the module into the local .m2 repository. In Maven parlance, this is referred to as 'installing' the module. The “maven-publish” plugin makes this easy to do by automatically creating a PublishToMavenLocal task for each MavenPublication in the publishing.publications container. Each of these tasks is wired into the publishToMavenLocal lifecycle task. You do not need to have `mavenLocal` in your `publishing.repositories` section.

The created task is named “publish«PUBNAME»PublicationToMavenLocal”.

> gradle publishToMavenLocal
:generatePomFileForMavenJavaPublication
:compileJava
:processResources UP-TO-DATE
:classes
:jar
:publishMavenJavaPublicationToMavenLocal
:publishToMavenLocal

BUILD SUCCESSFUL

Total time: 1 secs

The resulting task in this example is named “publishMavenJavaPublicationToMavenLocal”. This task is wired into the publishToMavenLocal lifecycle task. Executing “gradle publishToMavenLocal” builds the POM file and all of the artifacts to be published, and “installs” them into the local Maven repository.

At times it is useful to generate a Maven POM file for a module without actually publishing. Since POM generation is performed by a separate task, it is very easy to do so.

The task for generating the POM file is of type GenerateMavenPom, and it is given a name based on the name of the publication: “generatePomFileFor«PUBNAME»Publication”. So in the example below, where the publication is named “mavenCustom”, the task will be named “generatePomFileForMavenCustomPublication”.

model {
    tasks.generatePomFileForMavenCustomPublication {
        destination = file("$buildDir/generated-pom.xml")
    }
}

> gradle generatePomFileForMavenCustomPublication
:generatePomFileForMavenCustomPublication

BUILD SUCCESSFUL

Total time: 1 secs

All details of the publishing model are still considered in POM generation, including components`, custom artifacts, and any modifications made via pom.withXml.