How to publish to Maven Central

as of June 2024; based on material from Maven Central

Prerequisites

This guide aims at making it as easy as possible for you to publish your first artifact.
While it's absolutely possible to deviate from this approach, this guide assumes you're in possession of:

• a GitHub account
• a Linux machine for development (this example has been created with Ubuntu)
• and a Maven-based project waiting to be published
  • basic familiarity with Maven

Step-by-step guide

Register at Sonatype central

Hop on over to the Maven Central repository, and login via GitHub. This registers the io.github.your-username namespace for you, allowing you to publish artifacts matching this namespace.

Important

If you didn't do so yet, adapt the <groupId> of your artifact accordingly. You might use io.github.your-username or subgroups like io.github.your-username.foo.
Consider renaming the package names accordingly.

Configure Maven settings

For the artifact publishing, Maven needs access to your credentials. Since you don't want to share your credentials by listing them in the project's POM, these are put into the Maven settings, which are usually located at ~/.m2/settings.xml.

As credentials, you'll be using a user token:

1. go to your account on the Central Publisher Portal
2. click the button "Generate User Token"
3. copy the code snippet
4. add it to your existing [Maven settings][maven:settings], or create a new file containing

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <servers>
    <server>
      <id>central</id>
      <username>...</username>
      <password>...</password>
    </server>
  </servers>
</settings>

Tip

Consider using [Maven password encryption][maven:pw-encryption] for storing these credentials.

Set up artifact signing

Since you're using a Linux machine, gpg should be available.

1. create a key pair:

   gpg --batch --passphrase '' --quick-gen-key "[email protected]"

2. Note down the keyid (the hexadecimal code, usually the second line)

   gpg -k [email protected]

3. Distribute your public key

   gpg --keyserver keys.openpgp.org --send-keys YOUR-KEYID

Note

When using GitHub actions to publish, you have to "hand out" both key & passphrase anyway, thus we're using an empty passphrase to begin with.
If you'd rather want to use a passphrase, use gpg --gen-key to create a key.

Configure your project

Now, your Maven project needs to be configured with a number of plugins.

central-publishing-maven-plugin

We'll start with central-publishing-maven-plugin, which will upload the artifacts to the Maven Central repository:

<plugin>
  <groupId>org.sonatype.central</groupId>
  <artifactId>central-publishing-maven-plugin</artifactId>
  <version>0.5.0</version>
  <extensions>true</extensions>
  <configuration>
    <autoPublish>false</autoPublish>
    <deploymentName>${project.artifactId}:${project.version}</deploymentName>
    <waitUntil>validated</waitUntil>
  </configuration>
</plugin>

With this in place, we can try out the publish process!

mvn -B -ntp deploy

This will eventually fail because we're still missing a couple of things, yet your Deployments section in the Maven Central repository should list our attempt to publish something.
Go ahead and hit the Drop button.

Artifact signing, Javadoc & Sources

In order to publish to Maven Central, you need to sign all artifacts, and ship a Javadoc as well as the sources. Therefore, we need to configure more plugins:

<plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-gpg-plugin</artifactId>
    <version>1.6</version>
    <executions>
      <execution>
        <goals>
          <goal>sign</goal>
        </goals>
      </execution>
    </executions>
  </plugin>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-javadoc-plugin</artifactId>
    <version>3.6.3</version>
    <executions>
      <execution>
        <goals>
          <goal>jar</goal>
        </goals>
      </execution>
    </executions>
  </plugin>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-source-plugin</artifactId>
    <version>3.3.1</version>
    <executions>
      <execution>
        <goals>
          <goal>jar-no-fork</goal>
        </goals>
      </execution>
    </executions>
  </plugin>
</plugins>

Now, let's run the deployment process again:

mvn -B -ntp deploy

Note

Chances are that generating the Javadoc fails. Fix any errors that occur.

Tip

If you happen to have multiple GPG keys, you might have to configure the correct key to use (an indicator for that is Sonatype complaining with "Invalid signature for file").
There are several options to do this; using -Dgpg.keyname=... when calling Maven is suggested for now: when automating the release later on, only one key will be available.

Add missing information

The Maven execution is probably still going to fail, since some information in the POM is missing. Sonatype requires you to provide ^{(click here to see what I've added)}

• a project description
• a project URL
• a license
• developers information
• an SCM URL

Adapt the version

The only remaining thing to do is adapt the version, since SNAPSHOT versions cannot be released. Go ahead and adapt the version. Now if you run the Maven command again, you should have a successful build. The Deployments section will now show a Validated deployment.

Tip

If you think everything's working out, you can go ahead and publish your artifact now! 🎉

Automate the release process

For a more automated release process, we want the version numbering handled and have the released code tagged.

👷 coming soon

maven-release-plugin

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-release-plugin</artifactId>
  <version>3.0.1</version>
  <configuration>
    <releaseProfiles>release</releaseProfiles>
    <tagNameFormat>v@{project.version}</tagNameFormat>
  </configuration>
</plugin>

Release with GitHub Actions

👷 coming soon