Maven

The plugin template contains a pom.xml with release 25 and the same local API repository as the Gradle setup.

Depend on the API with provided scope:

<dependency>
  <groupId>dev.zernyth</groupId>
  <artifactId>api</artifactId>
  <version>0.8.0</version>
  <scope>provided</scope>
</dependency>

Build the local SDK artifact first, as described in Gradle, then package offline:

mvn -o package

-o needs Maven and its plugins to be available locally already. Never shade the API into your JAR.