Recently rails-integration 1.0 for JRuby was released.
Java web applications are typically packaged as WAR files in preparation for distribution and deployment to J2EE servers. Rails Integration allows the packaging of Ruby on Rails applications in a similar form, to enable seamless deployment to Java servers.
The documentation is available from:
http://www.headius.com/jrubywiki/index.php/Rails_Integration
Cheers,
Robert Egglestone