Maven Central Publish Skill

This skill provides a standardized workflow for publishing Java/Kotlin libraries to the Maven Central Repository using the modern Central Portal (via central-publishing-maven-plugin).

📋 Prerequisites

1. Central Portal Account: Sign up at central.sonatype.com.
2. Namespace Verified: You must have verified your groupId (e.g., io.github.username or com.yourdomain) in the portal.
3. User Token: Generated from the Central Portal (My Account -> Generate User Token).

🛠️ Environment Setup

1. Install Tools

Ensure maven, gnupg, and openjdk-17+ are installed.

# Ubuntu/Debian
apt-get install -y maven gnupg openjdk-17-jdk

2. GPG Configuration (Critical)

Maven requires GPG signing. For automated/headless environments, Loopback Pinentry is required.

# 1. Generate Key (if none exists)
gpg --gen-key

# 2. Configure Loopback (Prevent UI prompts)
mkdir -p ~/.gnupg
echo "allow-loopback-pinentry" >> ~/.gnupg/gpg-agent.conf
echo "pinentry-mode loopback" >> ~/.gnupg/gpg.conf
gpg-connect-agent reloadagent /bye

# 3. Publish Key
gpg --list-keys # Get your Key ID (last 8 chars or full hex)
gpg --keyserver keyserver.ubuntu.com --send-keys <KEY_ID>

3. Maven Settings (~/.m2/settings.xml)

Configure your Central Portal credentials.

<settings>
  <servers>
    <server>
      <id>central</id>
      <username>USER_TOKEN_USERNAME</username>
      <password>USER_TOKEN_PASSWORD</password>
    </server>
  </servers>
  <profiles>
    <profile>
      <id>release</id>
      <activation>
        <activeByDefault>false</activeByDefault>
      </activation>
      <properties>
        <gpg.executable>gpg</gpg.executable>
        <gpg.passphrase>YOUR_GPG_PASSPHRASE</gpg.passphrase>
      </properties>
    </profile>
  </profiles>
</settings>

📦 Project Configuration (pom.xml)

Your project MUST meet the Quality Requirements:

1. Coordinates: groupId, artifactId, version.
2. Metadata: name, description, url, licenses, developers, scm.
3. Plugins: Javadoc, Source, GPG, and Central Publishing.

Recommended Plugin Configuration

Add this to your <build><plugins> section:

<!-- 1. Source Plugin -->
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-source-plugin</artifactId>
    <version>3.3.0</version>
    <executions>
        <execution>
            <id>attach-sources</id>
            <goals><goal>jar-no-fork</goal></goals>
        </execution>
    </executions>
</plugin>

<!-- 2. Javadoc Plugin -->
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-javadoc-plugin</artifactId>
    <version>3.6.3</version>
    <configuration>
        <doclint>none</doclint> <!-- Prevent strict checks failing build -->
        <failOnError>false</failOnError>
    </configuration>
    <executions>
        <execution>
            <id>attach-javadocs</id>
            <goals><goal>jar</goal></goals>
        </execution>
    </executions>
</plugin>

<!-- 3. GPG Plugin (Best Practice: wrap in 'release' profile) -->
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-gpg-plugin</artifactId>
    <version>3.1.0</version>
    <configuration>
        <gpgArguments>
            <arg>--pinentry-mode</arg>
            <arg>loopback</arg>
        </gpgArguments>
    </configuration>
    <executions>
        <execution>
            <id>sign-artifacts</id>
            <phase>verify</phase>
            <goals><goal>sign</goal></goals>
        </execution>
    </executions>
</plugin>

<!-- 4. Central Publishing Plugin (The Magic Sauce) -->
<plugin>
    <groupId>org.sonatype.central</groupId>
    <artifactId>central-publishing-maven-plugin</artifactId>
    <version>0.7.0</version>
    <extensions>true</extensions>
    <configuration>
        <publishingServerId>central</publishingServerId>
        <!-- autoPublish: set to true to skip manual button click in portal -->
        <autoPublish>false</autoPublish> 
    </configuration>
</plugin>

🚀 Deployment

Run the deploy command with the release profile active:

mvn clean deploy -P release

Success Indicators:

• [INFO] Uploaded bundle successfully...
• [INFO] Deployment ... has been validated.

If autoPublish is false (recommended for first time), log in to central.sonatype.com, review the deployment, and click Publish.

❓ Troubleshooting

Error	Cause	Fix
401 Unauthorized	Invalid User Token in settings.xml	Generate new token in Central Portal. Ensure server ID matches.
GPG signing failed	No pinentry / wrong passphrase	Use pinentry-mode loopback config; Check gpg-agent.
Javadoc generation failed	Strict HTML checks	Add <doclint>none</doclint> to javadoc plugin config.
Invalid coordinates	GroupId mismatch	Ensure pom.xml groupId matches verified namespace in Portal.