Generate XML files required by App Engine for JRuby from a rackup file. This works from standard Ruby or JRuby, but you’ll need the rack gem.
Configure your app from within the ‘config.ru’ file:
AppEngine::Rack.app.configure( :application => 'simple', :version => 2 )
Now run xmlgen.rb and and your ready to go:
jruby -rubygems -e 'require "appengine-tools/genxml"'