JRuby demos from the JavaOne Script Bowl 2014 02 Nov 2014
ruby jruby javaone

This past October I was invited to represent JRuby in the JavaOne 2014 “Script Bowl.” A panel where community members from various projects which implement scripting languages on top of the JVM pitch their language to a live studio audience. This year’s panel consisted of a members from the Groovy, Clojure and Scala communities, and me representing JRuby of course.

The session consists of two segments, historically with one focusing on the capabilities of the language itself and the second segment focusing on the community built around the scripting language.

Instead of choosing to create a presentation, I took the road less traveled and created a series of live coding demos to demonstrate the utility of JRuby.

The collection of demos that I created can be found in this demo repository. For all of my demos I used Pry as a live JRuby interpreter to load and execute Java and Ruby code on the fly, which I hope made for a compelling presentation.

The following are the demos worth mentioning here:

ascii table from jar

In this demo I had grabbed some random Java code from the internet to print ascii-only formatted tables, and wrote some Ruby glue to make use of it. Copying and pasting this code into a running Pry session and you’ll get a nice table drawn in your console.

[16] pry(main)> puts make_table(headers, mails)
|           Subject           |           From           |
|         NOT SPAM WE PROMISE | |
| Important work related info | |
|       Don't forget the milk | |
=> nil
[17] pry(main)>

anonymous classes

This demo demonstrates how JRuby merges the use of anonymous classes in Java with Ruby’s concept of blocks. Instead of creating an anonymous class that implements the Runnable interface, we can just use pass a block of code to be executed inside of a java.lang.Thread.


This might be my favorite demo because it demonstrates one of the more compelling (to me) features of JRuby, it’s embeddability. In the “turtles” demo, I’ve got an entirely embedded and separate Ruby runtime environment, nested within an already existing Ruby runtime.

The result is that I can create isolated Ruby environments within the same JVM, which opens the door to all kinds of interesting sandboxing applications.

[44] pry(main)> require './turtles/first'
=> true
[45] pry(main)> puts "Our original JRuby has version: #{JavaOne::VERSION}".colorize(:magenta)
Our original JRuby has version: 1
=> nil
[46] pry(main)> puts

=> nil
[47] pry(main)> # Now let's load a the same module with a different version inside the runtime environment
[48] pry(main)> evaler.eval(runtime, "require './turtles/second'"); nil
=> nil
[49] pry(main)> evaler.eval(runtime, "puts \"Our embedded JRuby has version: \#{JavaOne::VERSION}\".colorize(:green)"); nil
Our embedded JRuby has version: 2
=> nil
[50] pry(main)>


The final demo that I gave is a little self-promiting, in that I demonstrated the capabilities of the jruby-gradle project. A project which allows you to use the Gradle tool for managing projects, obviating the need for Bundler, JBundler, Warbler and RVM.

During the demo I showed the build.gradle file which references a Ruby gem and demonstrated how to build a self-contained, self-executing .jar file with the tool:

% ./gradlew shadowJar

Then executed it:

% java -jar build/libs/jruby-gradle-example-all.jar
Hello from JRuby built with Gradle!

That is a jar file, running Java and Ruby code all from within the file, pretty spiffy if you ask me!

Predictably, JRuby didn’t win the Script Bowl, unpredictably Clojure did. The event was enjoyable, but for me my favorite part was creating the demos and honing my pitch for JRuby, which I’m sure I’ll have the opportunity to reuse in the future.