If you want to build or contribute to a kiegroup project, read this document.
It will save you and us a lot of time by setting up your development environment correctly. It solves all known pitfalls that can disrupt your development. It also describes all guidelines, tips and tricks. If you want your pull requests (or patches) to be merged into master, please respect those guidelines.
KIE (Drools, OptaPlanner and jBPM)
Code of the Drools rule engine, OptaPlanner constraint solver and jBPM workflow engine.