gistfile1.txt

~/projects/jruby/tmp ➔ cat ruby_util.rb 
require 'java'
require 'vendor/gems/environment'
require 'rake'

class MyRubyUtility
  java_signature ['String'] => 'void'
  def self.runRakeTask(name)
    ARGV.replace([name])
    Rake.application.run
  end

  java_signature ['String[]'] => 'void'
  def self.main(args)
    args.each {|arg| runRakeTask(arg)}
  end
end

~/projects/jruby/tmp ➔ jrubyc --java ruby_util.rb 
Compiling ruby_util.rb to class ruby_util
Generating Java class MyRubyUtility to MyRubyUtility.java
javac -cp /Users/headius/projects/jruby/lib/jruby-complete.jar:. MyRubyUtility.java

~/projects/jruby/tmp ➔ ls *.class
MyRubyUtility.class	ruby_util.class

~/projects/jruby/tmp ➔ cat Gemfile 
gem 'rake'

~/projects/jruby/tmp ➔ gem bundle
Calculating dependencies...
Updating source: http://gems.rubyforge.org
Caching: rake-0.8.7.gem
Installing rake (0.8.7)
Done.

~/projects/jruby/tmp ➔ cp ../lib/jruby-complete.jar rake_runner.jar

~/projects/jruby/tmp ➔ cat mymanifest
Main-Class: MyRubyUtility


~/projects/jruby/tmp ➔ jar ufm rake_runner.jar mymanifest ruby_util.class MyRubyUtility.class `find vendor -name \*.rb`
Jan 15, 2010 4:59:11 PM java.util.jar.Attributes read
WARNING: Duplicate name in Manifest: Main-Class

~/projects/jruby/tmp ➔ cat Rakefile 
require 'rake'

task :hello do
  puts "hello world!"
end

~/projects/jruby/tmp ➔ java -jar rake_runner.jar hello
(in /Users/headius/projects/jruby/tmp)
hello world!