Some of the companies that I interact claim that they will never switch to Ruby on Rails (or just plain ‘ol Ruby) for that matter. But with JRuby reaching 1.0 status (and currently on 1.0.2 with 1.1b1 already released) this changes the situation somewhat. Now it is possible to develop Rails apps and run it on your Java infrastructure that make use of native JDBC connections and a whole bunch more.

Pre-requisites

Since we want to run a Ruby on Rails app on a Java application server, we need to have a Java web container such as Tomcat, Jetty or Glassfish. In my case, I’ll be dropping the app into into a Glassfish domain. I guess that this should work just fine for Tomcat as well, but I have not verified this as yet.You also need a database and I will be using MySQL. If you are going to use another database, you need to make sure that the ActiveRecord-JDBC adapter has been developed for the DB. ActiveRecord is the ORM for Rails apps. Currently, there are ActiveRecord-JDBC adaptors for HypersonicSQL, Derby, MySQL and PostgreSQL. This is true for version 0.6 of ActiveRecord-JDBC. For other adapters, you will need to specify a proper JDBC URL in your application’s database configuration file, config/database.yml. This will make a lot more sense once you finish this exercise.All of the above (except or ActiveRecord, of course) should be stock standard goodies on any self-respecting Java development box. With this place, let’s get cooking.

Install JRuby

Download the JRuby bin distribution from the JRuby downloads page. At the time of writing this, 1.1b1 has been released. I am currently using the 1.02 release. Unzip/untar the file to somewhere convenient, add an environment variable JRUBY_HOME to point to the extracted directory, and add JRUBY_HOME/bin to your path.

	/> cd ~/tools	/> tar xzvf jruby-bin-1.02.tar.gz

	/> export JRUBY_HOME=~/tools/jruby-1.0.2

	/> export PATH=$PATH:$JRUBY_HOME/bin

You can verify your JRuby installation with:

	/> jruby -v

	ruby 1.8.5 (2007-11-01 rev 4810) [i386-jruby1.0.2]

 You will notice two versions being reported. The first tells us that the ruby implementation is version 1.8.5 and the second tells us that it is running on jruby 1.0.2 on i386 platform. If you are new to ruby, then you need to know that there are different implementations of ruby, with the definitive one called MRI (Matz’s Ruby Implementation – Matz is the original author of ruby). JRuby is an attempt at a complete port of MRI to Java, aiming to eliminate all dependencies on C libraries. This is one of the significant points about JRuby: it is pure Java.

Install RubyGems

The closest Java equivalent of RubyGems is Maven or Ant+Ivy. Gems is a library and dependency management tool for ruby. On a native ruby install, you would have to download and install RubyGems, but JRuby already has RubyGems rolled in. Take a peek at JRUBY_HOME/bin and you should see an executable file called gem. So, nothing more to do here. What the heck, let’s verify that RubyGem is working.

	/> jruby -S gem -v

	0.9.4

If $JRUBY_HOME/bin is first in your path, then you can try /> gem -v. The -S tells jruby to run the command that follows from $JRUBY_HOME.For the ruby folk, you should realize that JRuby has rolled in RubyGems version 0.9.4 which is as fresh as it comes.The closest Java equivalent of RubyGems that I can think of is perhaps Maven or ANT+Ivy. But RubyGems takes the prize hands-down for its absolute simplicity. Install rake and Rails below and see what I mean.

Install Rake

 Rake is a really good build tool for ruby (i.e a make for ruby, hence the goofy name). Once you start writing rake build scripts, you will wonder why one earth you thought ANT is nice. Anyway, let’s install rake.

	/> jruby -S gem install rake

Install Rails

Now that you’ve seen the goodness of RubyGems, install Rails and the ActiveRecord for JDBC.

	/> jruby -S gem install rails -v 1.2.6 -y --no-rdoc --no-ri

	/> jruby -S gem install activerecord-jdbcmysql-adapter --include-dependencies

We are deliberately installing Rails version 1.2.6. Rails 2.0.1 was released in early December 2007 and I have not taken 2.0.1 for a drive under jruby yet. So, we’ll stick to version 1.2.6 which is still great.

Get MySQL Ready

 We’re heading for the home straight with all this setup and configuration nonsense. Just a couple of things to do.

• Copy the MySQL JDBC driver to $JRUBY_HOME/lib.
• Create a MySQL database called testapp_development. Rails apps require three databases; one for development (suffixed _development), one for unit testing (suffixed _test and is wiped clean with every test run) and one for production (suffixed _production). For this exercise, we will just use the development database with full rights given to the MySQL user root with no pasword.

Create the Rails App

Now the fun starts! Finally!The next command will create a directory with the same name as your application. So, change to a directory that will contain your rails applications. In my case, I keep my applications in ~/projects/jruby.

	/> cd ~/projects/jruby

	/> jruby -S rails testapp

Now you should have a directory called testapp. Let’s see if our app works. Yes, in rails-land, the app can already be fired up!

	/> cd ~/projects/jruby/testapp

	/> jruby script/server

This fires up webrick, a built in http server with ruby support built in. Just point your browser to http://0.0.0.0:3000 and you should see the Rails happy page. Kill webrick by hitting CTRL+C.

Link up to your database

Edit the file config/database.yml and change it as follows. Note that the line socket: /tmp/mysql.sock must be removed.

	development:

  	  adapter: mysql

  	  database: testapp_development

  	  username: root

  	  password:

and

	production:

  	  adapter: mysql

  	  database: testapp_development

  	  username: root

  	  password:

 YML files are files that store configuration using YAML, which is a ” is a straightforward machine parsable data serialization format designed for human readability”.Now, let us inform the Rails app that we are using ActiveRecord-JDBC. Add the following to the file config/environment.rb just before the line Rails::Initializer.run do |config|.

  if RUBY_PLATFORM =~ /java/

    require 'rubygems'

    RAILS_CONNECTION_ADAPTERS = %w(jdbc)

  end

Create a table (the Rails way)

 Sure, we can write a simple SQL script to create the table we want, but for fun, let’s do it using some Rails sugar. You can keep your app running in webrick and still do the this. Just open up another command or shell, switch to your project directory and get going. This is one of the nicest bits of Rails – you can do most things without a restart of your application server.

	/> jruby script/generate migration AddGadgetsTable

This should have created a file db/migrate/001_add_gadgets_table.rb. Open this file and edit it as follows.

	class AddGadgetsTable < ActiveRecord::Migration

	   def self.up

	      create_table :gadgets do |table|

	         table.column :name,  :string, :null => false

	         table.column :color, :string, :null => false

	      end

	   end

	   def self.down

	      drop_table :gadgets

	   end

	end

After saving the file, run the following command to create the table. Actually, we’re migrating our existing database to version 001! Database refactoring is a definite goal of Rails. It may not be perfect, but it is certainly better than maintaining a bunch of SQL files.

	/> jruby -S rake db:migrate

 Even if you’ve never seen ruby before, the above is certainly readable and you can easily understand that we intend to create a table called gadgets with two columns name and color. Actually, there are more than these two columns. Have a look at the table structure and check that a primary key colum id has been added as well.

Generate Scaffolding to maintain the table

I know, I know, I know! Code generation for anything but the most trivial of code can be dramatic for newbies but real code takes a lot more effort. The point here is just to get some Rails code up and running so that we can deploy it in a Java application server. So, please bear with me.

	/> jruby script/generate scaffold gadget

Fire up webrick and visit the URL http://0.0.0.0:3000/gadgets. You should see a page with an empty list of gadgets and CRUD links.

Get ready to WAR

We need a few additional rake tasks to be able to build a WAR for our Rails application. The Goldspike plugin for Rails does just that. Let’s install the Goldspike plugin.

	/> jruby script/plugin install 

		svn://rubyforge.org/var/svn/jruby-extras/trunk/rails-integration/plugins/goldspike

All that’s required is to add the WAR dependency on the MySQL driver. What’s great about Goldspike is that we can declare Maven dependencies. Great combination: RubyGems for Ruby-land and Maven for JRuby-land! Open the file vendor/plugins/goldspike/lib/war_config.rb and add the following line to the list of # default java libraries block.

	add_java_library(maven_library ('mysql', 'mysql-connector-java', '5.0.5'))

Build the WAR

Now build the WAR using rake.

	/> jruby -S rake war:standalone:create

If you look in the root of your application directory, there should be a file testapp.war

Drop it into Glassfish

 Start your Glassfish domain, log in to the Glassfish admin console and click the Deploy Web Application link. Browse to the testapp directory and select the testapp.war file. If the app is not enabled, then select testapp, and click Enable.

See it in action

Point your browser to http://localhost:8080/testapp. You should see the Rails happy page, and http://localhost:8080/testapp/gadgets has the CRUD for our Gadget object.As easy as pie! And just as nice!