JRuby allows running Ruby code on the Java Virtual Machine. It has the advantages of accessing Java libraries from Ruby and embedding Ruby in Java applications. Gems mostly work the same in JRuby as Ruby MRI, though some with native extensions may need alternatives. ActiveRecord can use JDBC drivers in JRuby to connect to databases. Converting Rails apps may require updating gems to specify platforms. JRuby is well-suited for deployment on Java application servers using WAR files generated by the Warbler gem.

1. Introduction to JRuby
Anthony Juckel
ajuckel@gmail.com
@ajuckel

2. What is Ruby?
• Dynamic/duck-typed language
• Strongly object oriented
• Open class definitions
• Closures, blocks, and generators, oh my!

3. What is JRuby?

4. What is JRuby?
• JRuby == Ruby

5. What is JRuby?
• JRuby == Ruby
• JRuby != Ruby

6. What is JRuby?
• JRuby == Ruby
• JRuby != Ruby
• JRuby == Ruby++

7. How to install it?
• Download from jruby.org
• Install via rvm (but not on this wifi)

8. What can I do with it?
• Run Ruby code (1.8 or 1.9)
• Access Java libraries from Ruby
• Embed Ruby within a Java application

9. Lab 1: Install it!
• $ jruby -e ‘puts “Hello, World!”’
• $ jruby hello.rb
• $ jruby --1.9 hello.rb
• $ jirb
• $ jruby --1.9 -S irb
• $ JRUBY_OPTS=”--1.9” jirb

10. RubyGems
• Gems are units of software reuse in the
Ruby world
• Most Gems will work the same in JRuby as
in MRI
• Gems with native code _may_ work, but
seek alternatives

11. RubyGems
• Gems can install library files
• $ gem install json
• require ‘json’
• Gems can install scripts
• $ gem install rspec
• $ jruby --1.9 -S rspec

12. RubyGems
• Some gems are only of interest on JRuby
• jruby-openssl
• activerecord-jdbc-adapter

13. RubyGems
• Others have JRuby-specific versions
• nokogiri
• Uses libxml on MRI
• Uses Java XML libraries on JRuby

14. Lab 2: Gems
• $ gem search -r [gem] • jruby-openssl
• $ gem install [gem] • rspec
• $ gem list • json
• $ gem rdoc • bundler
• $ gem server • $ cd lab02
• $ rspec

15. Launch Time
• Yes, it can be a problem
• MRI: Quick to start, speed remains constant
• JVM: Slow to start, faster as hotspots are
optimized

16. Launch Time
• What to do about it?
• Tweak startup options to make JVM
startup as fast as possible

17. Launch Time
• JVM Options (prefixed with -J with jruby)
• -client (-J-client)
• -XX:+TieredCompilation
• -Xshare:dump / -Xshare:on

18. Launch Time
• JRuby Options
• -X-C (turn off compilation)
• --ng-server / --ng
• --ng will get faster after several
executions while the JVM optimizes

19. Launch Time
ITERATIONS=1000 rspec
1000
1.9.3
JRuby
100 JRuby -X-C
JRuby NailGun
10
1
0.1
1000 100000 10000000

20. Lab 3: Try it out
• -J-client
• -J-XX:+TieredCompilation
• -J-Xshare:on
• -X-C (turn off compilation)
• --ng-server / --ng

21. Launch Time (cont.)
• Can be improved, but for small tasks
cannot (yet?) match MRI
• What options are left?
• Guard
• Spork

22. Launch Time (cont.)
• Iterate using MRI
• Quickly verify small changes
• Integrate using JRuby
• Less frequent
• May have longer test suites, perhaps more
work, can afford to pay the start up cost

23. ActiveRecord
• An Object-Relational Mapping (ORM)
library
• Developed as part of Rails
• Maps database data to Ruby classes

24. ActiveRecord
• activerecord: Core functionality
• activerecord-*-adapter: Database-specific
adapter layer

25. ActiveRecord
• MRI’s activerecord-*-adapters use native
database libraries.
• JRuby can use JDBC drivers
• Must have JDBC adapter on classpath
• activerecord-jdbc*-adapters

26. Lab 4: ActiveRecord
• $ gem install activerecord-jdbc-adapter
• $ gem install activerecord-jdbcpostgresql-adapter
• $ gem install activerecord-jdbcsqlite3-adapter
• $ gem install activerecord-derby-adapter

27. Converting Rails App
• Rails itself (aside from ActiveRecord) is
very compatible with JRuby
• Gems used in any given project may or may
not be.
• jruby-lint can help identify potential issues.

28. Converting Rails App
• What are some known issues?
• Some ObjectSpace methods disabled by
default
• Native code use
• Kernel#fork / backtick operator / system
usage

29. Lab 5: Convert an App
• $ cd graphy # Rails app targeting MRI 1.9.3
• If you’ve got MRI installed, look at current
app
• bundle install
• rake db:create db:migrate db:seed
• rails s

30. Lab 5: Convert an App
• $ jrlint
• Update Gemfile
• :platforms => :jruby
• activerecord-jdbc*-adapter
• :platforms => :ruby
• pg, sqlite3

31. Lab 5: Convert an App
• After performing the updates, test the app
in JRuby
• Also test the app in MRI, if available
• Having dependencies properly scoped
should allow you to execute the app in
either environment

32. Lab 5: Convert an App
• Have an app along with you? Try
converting it now!
• Install/Run jrlint
• Update Gemfile (if necessary)
• bundle install
• Run your tests/specs or rails s.
• Ask questions!

33. Web App Deployment
• A Rails app is no good without a solid
deployment environment
• MRI deployment strategies leverage MRI
strengths
• Need JVM deployment options to leverage
JVM strengths

34. Web App Deployment
• MRI: HTTP server -> Ruby process(es)
• Mongrel / Unicorn
• Passenger
• JRuby: HTTP server -> JRuby threads
• Rails app: config.threadsafe!
• Be mindful of the threadsafety of your
dependencies

35. Web App Deployment
• Deploying in Java Application Server
• Most self-contained option: WARbler!
• JRuby web app -> deployable WAR
• Other options
• Trinidad / Glassfish Gem
• Torquebox

36. Lab 6: Deploy it
• We’ve ported an app to JRuby. Now
deploy it!
• $ gem install warbler
• $ warble config
• Browse/edit config/warble.rb
• $ warble war # builds WAR
• $ cp app.war [tomcat-home]/webapps

37. Questions?
• https://github.com/ajuckel/intro-to-jruby
• @ajuckel
• ajuckel@gmail.com