Publishing to your own Bintray Maven Repository Using Gradle

Publishing to your own Bintray Maven Repository Using Gradle

6 minute read

When working on an open source Java project, you always come to the point where you want to share your work with the developer community (at least that should be the goal). In the Java world this is usually done by publishing your artifacts to a publicly accessible Maven repository. This article gives a step-by-step guide on how to publish your artifacts to your own Maven Repository on Bintray.

Bintray vs. Maven Central

You might be asking why you should publish your artifacts to a custom repository and not to Maven Central, because Maven Central is THE Maven repository that is used by default in most Maven and Gradle builds and thus is much more accessible. The reason for this is that you can play around with your publishing routine in your own repository first and THEN publish it to Maven Central from there (or JCenter, for that matter, which is another well-known Maven repository). Publishing from your own Bintray repository to Maven Central is supported by Bintray, but will be covered in a follow-up article.

Another reason for uploading to Bintray and not to Maven Central is that you still have control over your files even after uploading and publishing your files whereas in Maven Central you lose all control after publishing (however, you should be careful with editing already-published files!).

Create a Bintray Account

To publish artifacts on Bintray, you naturally need an account there. I’m not going to describe how to do that since if you’re reading this article you should possess the skills to sign up on a website by yourself :).

Create a Repository

Next, you need to create a repository. A repository on Bintray is actually just a smart file host. When creating the repository, make sure that you select the type “Maven” so Bintray knows that it’s supposed to handle the artifacts we’re going to upload as Maven artifacts.

Obtain your API key

When signed in on Bintray, go to the “edit profile” page and click on “API Key” in the menu. You will be shown your API key which we need later in the Gradle scripts to automatically upload your artifacts.

Set up your build.gradle

In your build.gradle set up some basics:

plugins {
  id "com.jfrog.bintray" version "1.7.3"
  id "maven-publish"
  id "java"
}
    
buildscript {
  repositories {
    mavenLocal()
    mavenCentral()
    jcenter()
  }
}

repositories {
  mavenLocal()
  mavenCentral()
  jcenter()
}

version = '1.0.0'

The important parts are the bintray plugin and the maven-publish plugin.

The two repositories closures simply list the Maven repositories to be searched for our project’s dependencies and have nothing to do with publishing our artifacts.

Build Sources and Javadoc Artifacts

When publishing an open source projects, you will want to publish a JAR containing the sources and another JAR containing the javadoc together with your normal JAR. This helps developers using your project since IDEs support downloading those JARs and displaying the sources directly in the editor. Also, providing sources and javadoc is a requirement for publishing on Maven Central, so we can as well do it now.

Add the following lines to your build.gradle:

task sourcesJar(type: Jar, dependsOn: classes) {
    classifier = 'sources'
    from sourceSets.main.allSource
}

javadoc.failOnError = false
task javadocJar(type: Jar, dependsOn: javadoc) {
    classifier = 'javadoc'
    from javadoc.destinationDir
}

artifacts {
    archives sourcesJar
    archives javadocJar
}

A note on javadoc.failOnError = false: by default, the javadoc task will fail on things like empty paragraphs (</p>) which can be very annoying. All IDEs and tools support them, but the javadoc generator still fails. Feel free to keep this check and fix all your Javadoc “errors”, if you feel masochistic today, though :).

Define what to publish

Next, we want to define what artifacts we actually want to publish and provide some metadata on them.

def pomConfig = {
    licenses {
        license {
            name "The Apache Software License, Version 2.0"
            url "http://www.apache.org/licenses/LICENSE-2.0.txt"
            distribution "repo"
        }
    }
    developers {
        developer {
            id "thombergs"
            name "Tom Hombergs"
            email "tom.hombergs@gmail.com"
        }
    }

    scm {
        url "https://github.com/thombergs/myAwesomeLib"
    }
}

publishing {
    publications {
        BintrayPublication(MavenPublication) {
            from components.java
            artifact sourcesJar {
                classifier "sources"
            }
            artifact javadocJar {
                classifier "javadoc"
            }
            groupId 'io.reflectoring'
            artifactId 'myAwesomeLib'
            version '1.0.0'
            pom.withXml {
                def root = asNode()
                root.appendNode('description', 'An AWESOME lib. Really!')
                root.appendNode('name', 'My Awesome Lib')
                root.appendNode('url', 'https://github.com/thombergs/myAwesomeLib')
                root.children().last() + pomConfig
            }
        }
    }
}

In the pomConfig variable, we simply provide some metadata that is put into the pom.xml when publishing. The interesting part is the publishing closure which is provided by the maven-publish plugin we applied before. Here, we define a publication called BintrayPublication (choose your own name if you wish). This publication should contain the default JAR file (components.java) as well as the sources and the javadoc JARs. Also, we provide the Maven coordinates and add the information from pomConfig above.

Provide Bintray-specific Information

Finally, the part where the action is. Add the following to your build.gradle to enable the publishing to Bintray:

bintray {
	user = System.getProperty('bintray.user')
	key = System.getProperty('bintray.key')
	publications = ['BintrayPublication']

	pkg {
		repo = 'myAwesomeLib'
		name = 'myAwesomeLib'
		userOrg = 'reflectoring'
		licenses = ['Apache-2.0']
		vcsUrl = 'https://github.com/thombergs/my-awesome-lib.git'
		version {
			name = '1.0.0'
			desc = '1.0.0'
			released  = new Date()
		}
	}

}

The user and key are read from system properties so that you don’t have to add them in your script for everyone to read. You can later pass those properties via command line.

In the next line, we reference the BintrayPublication we defined earlier, thus giving the bintray plugin (almost) all the information it needs to publish our artifacts.

In the pkg closure, we define some additional information for the Bintray “package”. A package in Bintray is actually nothing more than a “folder” within your repository which you can use to structure your artifacts. For example, if you have a multi-module build and want to publish a couple of them into the same repository, you could create a package for each of them.

Upload!

You can run the build and upload the artifacts on Bintray by running

./gradlew bintrayUpload -Dbintray.user=<YOUR_USER_NAME> -Dbintray.key=<YOUR_API_KEY>

Publish!

The files have now been uploaded to Bintray, but by default they have not been published to the Maven repository yet. You can do this manually for each new version on the Bintray site. Going to the site, you should see a notice like this:

Notice

Click on publish and your files should be published for real and be publicly accessible.

Alternatively, you can set up the bintray plugin to publish the files automatically after uploading, by setting publish = true. For a complete list of the plugin options have a look at the plugin DSL.

Access your Artifacts from a Gradle Build

Once the artifacts are published for real you can add them as dependencies in a Gradle build. You just need to add your Bintray Maven repository to the repositories. In the case of the example above, the following would have to be added:

repositories {
    maven {
        url  "https://dl.bintray.com/thombergs/myAwesomeLib" 
    }
}

dependencies {
    compile "io.reflectoring:myAwesomeLib:1.0.0"
}

You can view the URL of your own repository on the Bintray site by clicking the button “Set Me Up!”.

What next?

Now you can tell everyone how to access your personal Maven repository to use your library. However, some people are sceptical to include custom Maven repositories into their builds. Also, there’s probably a whole lot of companies out there which have a proxy that simply does not allow any Maven repository to be accessed.

So, as a next step, you might want to publish your artifacts to the well-known JCenter or Maven Central repositories. And to have it automated, you may want integrate the publishing step into a CI tool (for example, to publish snapshots with every CI build). These issues will be addressed in upcoming blog posts.

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