Aaron Blohowiak's Blog

Thoughts on embedding JRuby January 28, 2011

I covered the initial JRuby-Lift integration on the LiftJR blog.

When trying to get this running, we did a bit of research.  The blogs and wiki posts were high-level or had too many options, so we ended up figuring things out using JRuby's excellent JavaDoc.  However, a "working man's guide" to embedding JRuby would have been useful.  I hope that you find this helpful:

  1. Import the right packages (org.jruby.*, org.jruby.embed.*, org.jruby.runtime.builtin.* )
  2. Instantiate your "Scripting Container". Pass in LocalContextScope.THREADSAFE as the ScriptingContainer constructor's parameter if you want thread safety (you probably do.)
  3. Use the scriptingContainer to eval the contents of an input stream (like a file with a class definition): scriptingContainer.parse(inputStream, filename).run()
  4. Get a handle to the jruby runtime: jrubyScriptingContainer.getProvider().getRuntime() and the thread context: runtime.getCurrentContext()
  5. Use the 'runtime' for getting a class by name, creating a new symbol and other global operations. Calling runtime.fastNewSymbol("pants") from java/scala will return a handle to :pants in your ruby environment. runtime.fastGetClass("ActiveRecord::Base") would return a handle to the relevant class.
  6. You use the thread context when actually invoking methods on objects. myRubyClass.callMethod(threadContext, methodName, Array(arg1, arg2...) )
  7. The JRuby has done an awesome job with getting the java interfaces right with the JRuby objects.  However, sometimes you just want a plain old java object.  Every RubyObject has a .toJava method; use it to get back the java equivalent of your ruby structure: .toJava(classOf[Boolean])

That should be enough to get you started.  Let me know if you have any questions.