$ sudo jruby -S gem install exceptional
Building native extensions. This could take a while...
/usr/local/share/jruby-1.2.0/lib/ruby/1.8/mkmf.rb:7: JRuby does not support native extensions. Check wiki.jruby.org for alternatives. (NotImplementedError)
from /usr/local/share/jruby-1.2.0/lib/ruby/1.8/mkmf.rb:1:in 'require'
from extconf.rb:1
ERROR: Error installing exceptional:
ERROR: Failed to build gem native extension.
/usr/local/share/jruby-1.2.0/bin/jruby extconf.rb
Gem files will remain installed in /usr/local/share/jruby-1.2.0/lib/ruby/gems/1.8/gems/json-1.2.0 for inspection.
Results logged to /usr/local/share/jruby-1.2.0/lib/ruby/gems/1.8/gems/json-1.2.0/ext/json/ext/generator/gem_make.out`