When we use Google App Engine, another problem pops up. GAE has 10MB limit per each file to upload (http://googleappengine.blogspot.com/2009/02/skys-almost-limit-high-cpu-is-no-more.html). The size of jruby-complete.jar is unfortunately over 10MB. The shell script to split jruby-complete.jar up into two jar archives has been introduced at http://olabini.com/blog/2009/04/jruby-on-rails-on-google-app-engine/. However, I learned the way in the blog was already obsolete when I filed JRUBY-3949. The smart way of doing that was already out there. The latest JRuby, I mean, JRuby 1.4.0dev in git HEAD has had a Rakefile to create jars.
This is what I acutually did on a terminal:
$ git clone git://kenai.com/jruby~main
$ cd jruby~main
$ export JRUBY_HOME=`pwd`
$ gem install rake
$ gem install hoe
$ cd gem
$ rake update
Then, jruby-core-1.4.0dev.jar and jruby-stdlib-1.4.0dev.jar was built in jruby~main/gem/lib directory.