Jarbler is a solution that packages Ruby applications in a jar file so that they can be executed on the target environment without a Ruby runtime environment under Java.
https://github.com/rammpeter/jarbler
The main motivation for the function in principle is to be able to run Ruby applications without Ruby being installed on the target system. This is particularly important for frequently used apps where the various runtime environments in Linux, Windows or Mac OS are not known beforehand. Java is a lower hurdle than Ruby.