JRuby and Hibernate

The beautiful thing about Rails on JRuby is that you have access to Java. Perhaps you have existing code you'd like to reuse or maybe there's some functionality in a Java library you'd like to use. Whatever the reason, it's good to know how to do it.

So today I created a new Rails app to demonstrate how to use Rails' controllers and views with some model classes from one of my earlier Java projects. My old app used the typical HibernateUtil singleton (section 1.2.5 of the Hibernate docs). I also liked the ActiveRecord pattern so my Java domain classes had some handy "find" methods. So in order to make this work in a Rails app, I installed the goldspike plugin:

script/plugin install http://jruby-extras.rubyforge.org/svn/trunk/rails-integration/plugins/goldspike

and then ran the rake task war:standalone:create

I copied the classes and lib directories from my old apps' WEB-INF directory to the WEB-INF directory in my Rails app and then generated a controller and modified it to look like this:

require 'java'
import 'com.example.domain.Person'
import 'com.example.util.HibernateUtil'

class PersonController < ApplicationController
  def list
    with_transaction do
      @people = Person.find_all.to_a
      @people.sort!{|p1, p2| p1.name.downcase <=> p2.name.downcase}
    end
  end
  
  def with_transaction
    begin
      tx = HibernateUtil.session_factory.current_session.beginTransaction
      yield
      tx.commit
      HibernateUtil.session_factory.current_session.close
    rescue
      tx.rollback
    end
  end
end

Finally, I added a list.rhtml template for the "list" action and voila! I have a Rails-ish app that uses Hibernate instead of ActiveRecord.