I have Ruby, Java and Clojure set up in my rails app. I’m using JRuby and I’m able to load the jar file created from Clojure. Here’s what I did.

$ rvm install jruby
$ rvm use jruby
$ brew install clojure
$ brew install leiningen
$ lein new default ttt  # this will also create function foo in ttt/core.clj
$ lein uberjar   # this will create a standalone jar file in directory "target"

Then you edit the Gemfile to include

gem "jrclj"

Create a file a.rb with the following sample code

#!/usr/bin/env ruby

require 'java'

Dir["#{File.dirname(__FILE__)}/ttt/target/*.jar"].each do |jar|
  require jar

require 'jrclj'

clj = JRClj.new "ttt.core"
clj.foo "chong"

Execute the code and you should see

chong Hello, World!

I have everything I need to create the Rails Tic Tac Toe.