Embedding JRuby in Java code using rvm jruby insta

Question

I'm trying to embed and evaluate ruby code from within a Java application. Instead of putting jruby-complete.jar in my classpath, I need to be able to use jruby environment that's installed with rvm. I can execute basic kernel code, but I'm having issues requiring standard libraries (fileutils, tmpdir, etc.).

I created the test file below that uses a JRuby installed via RVM, anyone should be able to compile+run it if you have a local rvm + jruby installation (change JRUBY_VERSION to a version installed). I realize the jruby.jar I'm referencing isn't the same as jruby-complete.jar, but I'm hoping there is a way to load standard libraries without downloading an external jar.

import java.io.File;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.logging.Logger;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;

public class Test {
    private final static Logger LOG = Logger.getAnonymousLogger();
    private final static String JRUBY_VERSION = "jruby-1.6.7";

    public static void main(String[] args) throws Throwable {
        final String rvmPath = System.getenv("HOME") + "/.rvm/rubies/";
        addFileToClasspath(rvmPath + JRUBY_VERSION + "/lib/jruby.jar");

        final ScriptEngine rubyEngine = new ScriptEngineManager().getEngineByName("jruby");
        rubyEval(rubyEngine, "puts 'hello world!'"); // works
        rubyEval(rubyEngine, "require 'tempfile'");  // fails to load 'tmpdir'
        rubyEval(rubyEngine, "require 'fileutils'"); // fails to load 'fileutils'
    }

    private static void rubyEval(ScriptEngine rubyEngine, final String code) {
        try {
            rubyEngine.eval(code);
        } catch (final Throwable e) { LOG.throwing(Test.class.getName(), "rubyEval", e); };
    }

    public static void addFileToClasspath(final String path) throws Throwable {
        final File file = new File(path);
        final URLClassLoader sysloader = (URLClassLoader) ClassLoader.getSystemClassLoader();
        final Class<?> sysclass = URLClassLoader.class;
        final Method method = sysclass.getDeclaredMethod("addURL", new Class<?>[] {URL.class});
        method.setAccessible(true);
        method.invoke(sysloader, new Object[] {file.toURI().toURL()});
    }
}

Answer 1

On an rvm installation, the core ruby files are installed alongside the jruby.jar (here for JRuby 1.7.2):

sebastien@greystones:~$ cd .rvm/rubies/jruby-1.7.2/
sebastien@greystones:~/.rvm/rubies/jruby-1.7.2$ find . -name fileutils.rb
./lib/ruby/1.8/fileutils.rb
./lib/ruby/1.9/fileutils.rb
sebastien@greystones:~/.rvm/rubies/jruby-1.7.2$ find . -name tmpdir.rb
./lib/ruby/1.8/tmpdir.rb
./lib/ruby/1.9/tmpdir.rb

You therefore need to add the correct ruby folder (which depends on the ruby version) to the classpath, for example:

    final String rvmPath = System.getenv("HOME") + "/.rvm/rubies/";
    addFileToClasspath(rvmPath + JRUBY_VERSION + "/lib/jruby.jar");

    // Here, add folder to classpath.
    System.setProperty("org.jruby.embed.class.path", rvmPath + JRUBY_VERSION + "/lib/ruby/1.9");