This short tutorial shows one of several possibilities to use a Ruby application within a Java application. It contains one complete example using Windows 7 (doing the same on OSX or Linux should not be difficult).
JRuby can be downloaded here. Use JRruby 1.7.23 (this corresponds to Ruby 1.9.3) for applications which are supposed to run on Java 1.6 (a.k.a. Java 6) or higher, and the most recent JRuby 9.x (this corresponds to the Ruby 2.2 line) for applications running on Java 1.7 (a.k.a. Java 7) and higher. You will need two download distributions: One is the platform-specific distribution, which you need for executing a jruby command - this would be for example JRuby 1.7.23 Windows Executable (x64). The other one is the (platform-independent) jar file, which is used to deliver the application, i.e. running it with java. This is called jruby-complete, and on the download page it would be found under the name of, for instance, JRuby 1.7.23 Complete .jar.
You can verify your JRuby- and Java-version after installation with
This also shows the equivalent Ruby version implemented by JRuby, for example:
jruby 1.7.23 (1.9.3p551) 2015-11-24 f496dd5 on Java HotSpot(TM) 64-Bit Server VM 1.7.0_79-b15 +jit [Windows 7-amd64]
The example application, which also can be downloaded, comprises of a Java main program, and classes written in Java and Ruby. One of those Java classes "talks" to the Ruby world, passes Java objects to Ruby and returns Ruby objects as well as Java objects created within the Ruby world. The application doesn't do anything useful and just demonstrates various aspects of the interoperability between Java and JRuby.
I don't show every possibility to connect Java and Ruby, but enough to allow anyone build a mixed Java-Ruby-application.
The connection between Java and JRuby is known under the name The Red Bridge.
I tested the example with Java 1.7 and JRuby 1.7.23 on Windows 7.