JRuby on Heroku via Clojure

The big news about "Matz to Heroku" reminded me another news from Heroku. That's "Clojure on Heroku"!!! Yes, this news was for me, a JVM language lover. JVM has started running on Heroku, which means all JVM languages run on Heroku via Clojure. When I heard the news, I thought I should have tried that. So, today, I actually tried to run JRuby from Clojure. Happily, JRuby easily ran on Heroku.

I read these two, Clojure on Heroku and Getting Started With Clojure on Heroku/Cedar, and tried. These are good documents to get started. Following the documents, I wrote project.clj below:

(defproject hello-world "0.0.1"
  :dependencies
    [[org.clojure/clojure "1.2.1"]
     [org.jruby/jruby-complete "1.6.3"]
     [ring/ring-jetty-adapter "0.3.9"]])

This dependency is parsed by Leiningen(https://github.com/technomancy/leiningen). The format is [maven's groupId/ArtifactId version], so I added [org.jruby/jruby-complete "1.6.3"] in project.clj. Next, I edited web.clj as in below:

(comment "filename: web.clj")

(ns demo.web
  (:use ring.adapter.jetty))

(import '(org.jruby.embed ScriptingContainer))
(def c (ScriptingContainer.))
(def version (. c runScriptlet "JRUBY_VERSION"))

(defn app [req]
  {:status 200
   :headers {"Content-Type" "text/plain"}
   :body (str "Hello JRuby " version " from Clojure!")})

(defn -main []
  (let [port (Integer/parseInt (System/getenv "PORT"))]
    (run-jetty app {:port port})))

In this file, I imported org.jruby.embed.ScriptingContainer class. It is RedBridge. Then, I instantiated ScriptingContainer and evaluated JRUBY_VERSION constant which was assigned to "version" so that I could use later.

When I uploaded this project and requested from a browser, I could see the JRuby's version.
OK, JRuby worked!


I tried one more since just showing JRuby version is too simple. The second attempt was somehow proxy like code using Ruby's open-uri standard library. I wrote src/demo/jruby.clj as in below:

(comment "filename: jruby.clj")

(ns demo.jruby
  (:use ring.adapter.jetty))

(import '(org.jruby.embed ScriptingContainer))
(def c (ScriptingContainer.))

(defn app [req]
  {:status 200
   :headers {"Content-Type" "text/html"}
   :body (. c runScriptlet "require 'rubygems'; require 'open-uri'; f = open('http://www.ruby-lang.org/').read")})

(defn -main []
  (let [port (Integer/parseInt (System/getenv "PORT"))]
    (run-jetty app {:port port})))

In jruby.clj, I changed text/plain to text/html of response header and, in response body part, put a result of evaluating a short Ruby code. As you know, this tiny Ruby code reads HTML from http://www.ruby-lang.org/ and returns the contents. Then, changed Procfile as in below because the file is jruby.clj this time.

Procfile

web: lein run -m demo.jruby

Again, upload all to Heroku. Browsing the url, I got the output below:
Yes! It worked!



My next attempt will be Rubygems to Clojure on Heroku. I think Rubygems will possibly cover something missing in Clojure.



You might be interested about using Rubygems from Clojure. My presentation at RubyConf 2010, "Rubygems to All JVM Languages" (slide: http://servletgarden-point.appspot.com/slideshow, sample code: https://github.com/yokolet/rubyconf2010), might help you understand.