Minimum requirement for the JDK is Java 7. Get it here. GreenLightning has module compatibility up to Java 9.
Maven
If you have developed applications using Java before, Maven will be familiar. GreenLightning uses Maven as well as Maven central for releases and snapshots. Dependencies inside GreenLightning and its related projects are all managed using Maven.
To install Maven on your machine, please follow this guide on the Maven page.