In the process of updating to Lucene version 6.3.0 we switched the main build system to Gradle. The source code is now better organized, following the structure of Maven with all the source divided into main and test, and the resources being separated. It allows for the use of Maven repositories, automates most tasks out-of-the-box and is extended easily using the Groovy programming language.
Gradle also comes with a wrapper, so as long Java is installed, the build process is fully automated and does not need additional software installed.
Moreover, build.gradle files can be easily used to import projects into JetBrains IDEA. LireDemo and SimpleApplication are sub projects with their own build.gradle files. Checkout the new structure at https://github.com/dermotte/lire.