If you're trying to use jruby on rails, and you see an error like this:
GEM_HOME=~/.jrubygem jruby -S rake db:create:all
!!! The bundled mysql.rb driver has been removed from Rails 2.2. Please install the mysql gem and try again: gem install mysql.
no such file to load -- mysql
(See full trace by running task with --trace)
The solution is to run script/generate jdbc:
GEM_HOME=~/.jrubygem jruby -S script/generate jdbc
See Nick Sieger's blog for more detail.