In previous articles, I discussed how to publish snapshots
to oss.jfrog.org and how to publish releases to Bintray using
Gradle as a build tool. While this is very helpful already, you can get better exposure
for your release by publishing it to the JCenter
and / or Maven Central repositories
because those are widely known and supported by build tools. This article explains how to
publish a release from your Bintray repository to JCenter and Maven Central.
Example Code
This article is accompanied by a working code example on GitHub.JCenter vs. Maven Central
Before we go into the details of publishing to JCenter and Maven Central, let’s disuss the difference between the two. Both are publicly available Maven repositories that host releases of open source libraries.
Maven Central is operated by Sonatype, the company behind the Nexus software that is widely used to host Maven repositories (and hosts Maven Central itself).
JCenter is operated by JFrog, the company that created Bintray and Artifactory (which is used to host JCenter). JCenter is younger than Maven Central, giving it an edge in terms of user experience and simple workflows because the developers had more time to learn.
Since JCenter is a mirror of Maven Central that contains everything Maven Central contains plus some extra, you could simply include JCenter into your build tools and get access to all releases you could wish for. However, Maven Central is still more widely known and supported out-of-the-box in more build tools, so you might want to publish your release in both repositories.
In the following, we will discuss the steps necessary to synchronize a repository on Bintray with JCenter and Maven Central so that all releases to that repository are automatically published to both public repositories. If you don’t have uploaded your release to Bintray yet, read this article which explains the necessary steps.
Publish to JCenter
Syncing a Bintray repository to JCenter is easy as pie. Simply go to your package in the Bintray UI and klick the button “Add to JCenter”. In the dialog you can also check the checkbox “host my snapshot artifacts on oss.jfrog.org” to be able to publish snapshots (more on snapshots here).
Submit the form and wait until you get a response. This may take a working day or so, since the approval is a manual process. Then, you’ll find a response in your inbox on Bintray and you’re ready to publish to JCenter. Every time you publish an artifact to Bintray, it will automatically be mirrored to JCenter without anything else to do.
To publish manually, click the “Publish” link shown below after you uploaded some files.
To publish automatically from a Gradle build, add the publish flag to the bintray configuration:
bintray {
...
pkg {
...
}
publish = true
}
Publish to Maven Central
Syncing with Maven Central requires a little more effort. Here’s what to do:
Set up a Sonatype Account
Maven Central is hosted on a Nexus instance that requires a login to publish releases. Thus, you need to register and request the group name you want to publish your artifacts under. This guide explains the necessary steps. There is a manual process involved on Sonatype’s side so be patient :).
Link Your Bintray Account with Your Sonatype Account
Next, you can add your Sonatype credentials to your Bintray Account under “Edit Profile -> Accounts”.
If you’re not comfortable with trusting your Sonatype credentials to Bintray, you can also enter the credentials each time you want to sync your repository in the step “Sync with Maven Central”.
Next, we need to sign our artifacts, since that is a requirement for all artifacts published on Maven Central.
Sign with Bintray’s Key
The easy way to sign your artifacts is to let Bintray do the work. Simply check “GPG sign uploaded files using Bintray’s public/private key pair.” in the settings of your Bintray repository. Done.
Sign with your own Key
If you want to sign your artifacts with your own key, you first need to create a GPG key pair and add the public and private keys to your Bintray profile under “Edit Profile -> GPG Signing”.
Additionally, we need to add the gpg closure to the Bintray gradle plugin so that
when gradle publishes artifacts to Bintray, they are automatically signed with
the private key associated to your Bintray profile:
bintray {
...
pkg {
...
version {
...
gpg {
sign = true
}
}
}
publish = true
}
For a full example have a look at my diffparser project.
Note that the key pair you upload to your Bintray profile should be a special key pair for exactly the purpose of publishing your artifacts through Bintray. You’re giving away your private key, after all, so you don’t want it to be a key that is also used for something else.
Again, if you don’t feel comfortable with providing a private key to Bintray, you can use a Gradle plugin like the Signing Plugin to create the signatures from the Gradle build on your machine or your CI server (however, then you still have to provide the private key to the CI server, which probably is not much better…).
Sync with Maven Central
Once the above steps are taken, navigate to the package you want to publish in the Bintray UI. Open the “Maven Central” tab and click on “Sync”. You may have to wait a couple minutes and then the Bintray UI shows if the syncing was successful. Note that you have to hit this button manually each time you want to release a new version to Maven Central.
Conclusion
This article discussed the steps necessary to sync a Bintray package to JCenter and Maven Central to get the best exposure for your open source releases. Syncing to JCenter is easier than syncing to Maven Central, but to get even more exposure, it might still be worth it to take the steps to also publish to Maven Central.
