import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.jruby.embed.ScriptingContainer;

public class RubyLauncher {
	private ScriptingContainer container;
	private Object receiver;
	
	private RubyLauncher(String initialRequire, String rootRubyClass, String rootMethod) {
		String bootstrap = 
            "require \"" + initialRequire +  "\"\n"+
            "class Bootstrap \n" +
            "   def execute root_object  \n" +          
            "       " + rootRubyClass + ".new." + rootMethod + "(root_object) \n" +
            "   end    \n" +      
            "end \n" +
            "Bootstrap.new";
		
		container = new ScriptingContainer();
		String currentDir = container.getCurrentDirectory();
		String[] paths = {currentDir + "/bin"};
		List<String> loadPaths = Arrays.asList(paths);
		//container.getProvider().setLoadPaths(loadPaths); // JRuby 1.4
		container.setLoadPaths(loadPaths); // JRuby 1.5
		receiver = container.runScriptlet(bootstrap);
	}
	
	private void call(Object obj) {
		container.callMethod(receiver, "execute", obj, null);
	}
	
	public static void main(String[] args) {
		Map<String, Object> root = new HashMap<String, Object>();
		root.put("name", "david");
		RubyLauncher launcher = new RubyLauncher("ruby/ruby_root.rb", "RubyRoot", "start");
		launcher.call(root);
	}

}

class RubyRoot

  def start( root )
    puts root.toString
  end

end

Above produces:

{name=david}

I used Eclipse Java project to run the code, so I had a path, "bin," in a load path. Please change the path to fit it in yours. Also, change the first argument of RubyLauncher constructor so that ruby_root.rb can be found from the load path. I had ruby_root.rb file under bin/ruby directory when I ran the code.