PF4J : Maven

In your pom.xml you must define the dependencies to PF4J artifacts with:

<dependency>
    <groupId>org.pf4j</groupId>
    <artifactId>pf4j</artifactId>
    <version>${pf4j.version}</version>
</dependency>    

where ${pf4j.version} is the last pf4j version.

You may want to check for the latest released version using Maven Search

Also you can use the latest SNAPSHOT via the Sonatype Maven Repository. For this, you must add below lines in your pom.xml:

<repositories>
    <repository>
        <id>sonatype-nexus-snapshots</id>
        <url>https://oss.sonatype.org/content/repositories/snapshots</url>
        <releases>
            <enabled>false</enabled>
        </releases>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
    </repository>
</repositories>

PF4J Plugin Framework for Java

Maven