The Java code in the subproject productdata-RDF4J-java was generated with OLGA, the Ontology Library Generator.
This automatically generated code folder is a companion to the rest of the Linked Data project. This automatically generated code is a representation of the ontology file which is further described here.
For more background information on the model driven approach and OLGA, please read the article A Model Driven Approach Accelerating Ontology-based IoT Applications Development.
The folder productdata-RDF4J-java is embedded in the sbt project with the rest of the Scala code, but it can
also be compiled standalone. To do that, execute the following command within the folder productdata-RDF4J-java:
mvn clean install
Notice that this won't work from the root folder, for the simple reason that it's a sbt-based project with Scala code.