1. JRuby
The Best of Java
and Ruby
by
Evgeny Rahman
Image source: https://github.com/jruby/collateral/ by Tony Price (tonyxprice)
JRuby is Copyright (c) 2007-2012 The JRuby project

2. A little bit about Ruby
• Created in 1993 by Yukihiro Matsumoto
(“Matz”).
• An object-oriented scripting language.
• Guiding philosophy - a language that feels
natural to programmers.
• Principle of least surprise.

3. Adoption
• First English mailing list appeared in 1999.
• “Programming Ruby” (aka “The Pickaxe
Book”) by Dave Thomas and Andy Hunt
released in 2000.
• Interest grew considerably in 2005 because of
the Rails framework.
• 225,000 Ruby projects on GitHub.

4. Examples
• The all-important Hello World:
puts "Hello World"
• Array iteration:
['a', 'b', 'c', 'd', 'e'].each { |x| puts x }
• Hash operations:
animal_sounds = { :dog => 'woof', :cat => 'meow'}
animal_sounds[:dog]
#=> 'woof'

5. Examples
• unless:
"Unicorns exist!" unless unicorns.empty?
• Blocks:
flights = flights.sort do |flight_a, flight_b|
flight_a.price <=> flight_b.price
end
• Loops:
100.times { |i| puts "The number is #{i}" }

6. JRuby
• Created by Jan Arne Petersen in 2001.
• Ruby implementation that runs on the JVM.
• Current core team of nine developers.
• Currently 1.7.0 is out in preview.
• Supports MRI 1.8.7 and 1.9.3.
• Code is JIT and AOT compiled into JVM
bytecode.

7. Advantages
• Java interop – use the Java ecosystem and
your existing libraries.
• Threading – real, JVM multithreading.
• InvokeDynamic in Java 7 – optimization in
performance for JRuby.
• Deployment – several options, including
familiar, Java ones.

8. Java interop – simple!
require 'java'
java_import 'java.lang.Math'
puts java.lang.Math::PI
#=> 3.14159265358979

9. Java interop – libraries
require 'java‘
require 'path/to/yourlib.jar'
Now if you do:
java_import "org.your.lib.YourClass"
Your class is available as
Java-style: org.your.lib.YourClass
Ruby-style: Java::YourLib::YourClass
and directly referenced as
YourClass
More information: https://github.com/jruby/jruby/wiki/CallingJavaFromJRuby

10. Caveats
• Gems with C extensions – use alternatives.
• JVM startup time – TDD, scripting.
• No compilation – more testing, more
discipline.
• Development-Deployment gap.

11. Deployment
• This was the missing link for Ruby in the enterprise *
• Warbler – create a WAR and deploy it to a Java EE container.
• jet.pack – package your JRuby rack app for Jetty.
• Trinidad – run Rails or Rack applications on embedded Tomcat container.
• Mizuno – jetty-powered server for JRuby in the style of Thin or WEBRick
• Torquebox – JBoss AS-based Ruby application platform
• Rack (Rails, Sinatra), JDBC, Daemons, Scheduled Jobs, Messaging,
Asynchronous Tasks
• “Deploying with JRuby” – Joe Kutner, The Pragmatic Bookshelf.
* My humble opinion

12. Community
• Really nice people!
• Core team is great, but there are also many
other contributors.
• Blogs, Twitter, IRC, Mailing Lists, Wiki, Issue
tracker.
• JRubyConf organized every year since 2009 –
this year’s was in Minneapolis, MN.
• Best place to start: jruby.org

13. Resources
• http://jruby.org/
• http://github.com/jruby/ - GitHub
• http://jira.codehaus.org/browse/JRUBY - issue
tracker
• http://kenai.com/projects/jruby/pages/Home -
old wiki
• https://github.com/jruby/jruby/wiki/ - new wiki
• #jruby IRC channel on FreeNode IRC
• @jruby on Twitter