Thoughts on JRuby

Alon Salant ·

At Carbon Five we have built our professional consulting practice on the solid foundation of enterprise Java development. In 2007 we added Ruby and Ruby on Rails as development tool and framework that complement our existing values and process in many fantastic ways.

Looking forward, I want to be sure that we take maximum advantage of our existing knowledge and new learning in both Java and Ruby. I have high hopes for JRuby as a valuable bridge that spans both languages and gives developers the flexibility to use the strengths of the two. Sun appears to feel the same way as they have hired the two core JRuby developers, Charles Nutter and Thomas Enebo, to work on JRuby full time.

In preparation for more specific posts, here are some light musings on JRuby.

JRuby 1.0

Released mid-2007 JRuby 1.0 was focused on Ruby compatibility. The idea is that any Ruby script or application you can run with the native C Ruby interpreter, you can run with JRuby. The success of this effort can be observed with Ruby on Rails applications now running on JRuby. Of course, there are some limitations.

In addition to running pure Ruby, JRuby can access the Java environment in which it is running. You get the Ruby niceties that you would expect like optional conversion of CamelCase method names to underscore_separated.

list =
list.add_all [2, "three"]

Any Java classes in the Java classpath are available to your JRuby script. Additionally, you can ‘require foo.jar’ to make it available on your classpath at runtime.

You can also extend Java classes in JRuby.

class MyList < java.util.ArrayList
  def say_hi

Internally, many core Ruby classes have been rewritten to delegate to core Java classes.

JRuby 1.1

JRuby 1.1 is presently in beta. The top priorities for JRuby 1.1 are performance and Java integration. Ruby is not fast. JRuby 1.0 was worse. Performance was not a priority for 1.0 and the consensus is that there are a lot of easy performance wins that it is now time to take advantage of. In his blog, Charles Nutter states:

Straight-line execution is now typically 2-4x better than Ruby 1.8.6. Rails whole-app performance ranges from just slightly slower to slightly better, though there have been reports of specific apps running many times faster.

Java Integration

Java integration refers to features for the using Ruby from Java rather than Java from Ruby as I discuss above. When I first started looking at JRuby Christian and I were working on a Java library to manage database migrations ala RoR and some other neat tricks we’ve seen along the way. (More on that later.) I thought it would be cool if you could write migrations using ActiveRecord’s migration features and invoke them from Java. I found myself looking for the easy means to invoke Ruby from Java. Some of this is in place with more slated for future JRuby versions.

The Spring Framework provides JRuby integration through which you can expose Ruby classes as Spring-managed beans. This example of using the RedCloth Ruby library to format text in a Java application is a pretty slick example of how this works.

This post does point out one issue that I ran into with using Ruby from Java – RubyGems. Gems are Ruby libraries available from central repositories and installed on the system running Ruby. For Java applications, this dependency on system-installed resources is lame. To address this issue, I’ve spent some time working on a solution for packaging Ruby gem dependencies in Java applications. More on JRubyGems coming soon.