I untar JRuby 1.1.1, and then the following happens when I attempt to list out of date gems:
$ jruby -S gem outdated
Bulk updating Gem source index for: http://gems.rubyforge.org/
ERROR: While executing gem ... (Gem::RemoteSourceException)
Error fetching remote gem cache: NameError: uninitialized constant Gem::RemoteFetcher::StringIO reading
I get this same error when I try to do the following:
$ jruby -S gem sources -a http://gems.github.com
I've also tried this on Linux with Java 1.6, and I get the same error.
If I open up jruby-1.1.1/lib/ruby/site_ruby/1.8/rubygems/remote_fetcher.rb and add require 'stringio' to the top, it fixes the problem.