Eclipse's Java Compiler packaged as a gem (not just) for JRuby. ECJ is part of Eclipse's JDT
add the gem to your Gemfile:
gem 'ecj'
or install "plain" old-school:
$ gem install ecj
if you only need the ecj.jar it's packaged as a dependent gem:
$ gem install ecj_jar
require 'ecj/jar'
CLASSPATH << ECJ::JAR
or obviously in your Gemfile:
gem 'ecj_jar', require: 'ecj/jar'
ECJ.load_jar
TODO: WIP
Copyright (c) 2014 Karol Bucek. See LICENSE (http://www.eclipse.org/legal/epl-v10.html) for details.