DDevelopment & Design

Geecon 2011 – day 2

And now for part 2 of my visit to Geecon 2011!

1. Jim Webber “Revisiting SOA for the 21st century”

Now this was awesome! Jim Webber, a former ThoughtWorks employee, now Neo4j evangelist (in Neotechnology) described his views on how SOA should look – according to him. This was presented previously, on other occasions as his “Guerilla SOA” talk – generally he advocated for REST based services, loose contracts (stating that WSDLs are too verbose and code generation is evil).

Jim mentioned Martin Fowler’s article on integration databases but I couldn’t find it anywhere – thou the topic looks interesting. He also recommended BDD and exposing tests on the web for the end user to use them as early as possible.

One big point he made his case with was not relying on enterprise software. Simple tools can do much better job. He compared implementing Web Services security (Secured SOAP over HTTP over TCP IP) to REST based service accessed through HTTPS – basic and easily testable with tools like curl.

Great talk. One of the best!

2. Staffan Noteberg “Regex – the future programming”

I must confess, that this did not go too well. The whole talk was well prepared and laid out but it lacked depth. It was pretty basic introduction to regex. From the presentation’s subject I was rather prepared for some novel uses of regex – like for example: showing how to filter big volume of data with simple regex or sth.

But the talk was fun, Staffan is a good speaker. He is also an author of pomodoro technique book – I intend to read sth abut this technique and this may be a nice start

3. Bartosz Kowalewski “Is OSGI ready for wide adoption?”

If it comes to titles I tend to rely on them pretty heavily, however strange it may seem. This time I also did – and the whole talk did not give me a definitive answer to the stated question.

Sure, the presentation was informative, but it described some OSGI specific, quite low level stuff. Of course, if you want to use OSGI – even by leveraging application server with OSGI under the hood – you should know a fair bit about the technology itself. Even thou the AS does a good job of hiding OSGI container specifics from the developer, in case of problems it’s better to be well informed. All in all – the talk gave too little information for me.

4. Vaclav Pech “Pick low hanging fruit”

“Parallelism is not hard, multithreading is” – this was the key sentence of the presentation. The speaker showed how to introduce concurrency into normal java/groovy code by sprinkling it with concurrency powder. Easy enough! With GPars library he showed:

  • running processing tasks with thread pools
  • testing concurrent code
  • Fork/join Thread Pool – multiple thread queues (note to self: fork/join is good for hierarchical problems)
  • low-hanging fruits:
    • async calculations
    • fork/join
    • dataflow
    • parallel collection processing
  • Actors are great – use GPars or Akka, is sufficient to use @ActiveMethod and @ActiveObject annotations and Actors are usable in OO-world

Good talk, well received!

5. Anton Arhipov “Bytecode for discriminating developers”

Technical introduction to the world of bytecode, jvm specification details. I’ve drifted away to some other topics – really – can’t recall what this was all about.

6. Andreas Almiray “Polyglot Programming”

This was a nice talk covering Groovy, Scala and Closure. The whole point of it was to show how cool it is to play with emerging JVM languages. They are not only fun but also useful. What’s more, they bring freshness to java world, injecting it with some new paradigms and methodologies. It is easier to incorporate new ideas into younger JVM languages than to the mature Java.

7. Jim Webber “A pragmatic introduction to Neo4j”

And Jim Webber again, this time with some Neo4j evangelism. First came some taxonomy information on NoSQL databases (Not Only SQL) as a whole – than some specific examples of problems solvable with graph databases – and Neo4j is a graph database.

Main points of Jim’s talk were:

  • sharding a database is important for scalability
  • series data – should be OK to use Neo4j as their storage

Conclusion

These were all the sessions I attended. On Saturday there was a Hacker-garden, but neither I had time nor will to stay – the topics were very interesting and I’d definitely like to experience such an event, but after 2 days of continuous talks I was rather tired.

To sum up, 2011’s Geecon was a great experience, with lots of interesting talks and lots of new inspirations. Keep up the good work guys!

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DDevelopment & Design

Clojure web development – state of the art

It’s now more than a year that I’m getting familiar with Clojure and the more I dive into it, the more it becomes the language. Once you defeat the “parentheses fear”, everything else just makes the difference: tooling, community, good engineering practices. So it’s now time for me to convince others. In this post I’ll try to walktrough a simple web application from scratch to show key tools and libraries used to develop with Clojure in late 2015.

Note for Clojurians: This material is rather elementary and may be useful for you if you already know Clojure a bit but never did anything bigger than hello world application.

Note for Java developers: This material shows how to replace Spring, Angular, grunt, live-reload with a bunch of Clojure tools and libraries and a bit of code.

The repo with final code and individual steps is here.

Bootstrap

I think all agreed that component is the industry standard for managing lifecycle of Clojure applications. If you are a Java developer you may think of it as a Spring (DI) replacement - you declare dependencies between “components” which are resolved on “system” startup. So you just say “my component needs a repository/database pool” and component library “injects” it for you.

To keep things simple I like to start with duct web app template. It’s a nice starter component application following the 12-factor philosophy. So let’s start with it:

lein new duct clojure-web-app +example

The +example parameter tells duct to create an example endpoint with HTTP routes - this would be helpful. To finish bootstraping run lein setup inside clojure-web-app directory.

Ok, let’s dive into the code. Component and injection related code should be in system.clj file:

(defn new-system [config]
  (let [config (meta-merge base-config config)]
    (-> (component/system-map
         :app  (handler-component (:app config))
         :http (jetty-server (:http config))
         :example (endpoint-component example-endpoint))
        (component/system-using
         {:http [:app]
          :app  [:example]
          :example []}))))

In the first section you instantiate components without dependencies, which are resolved in the second section. So in this example, “http” component (server) requires “app” (application abstraction), which in turn is injected with “example” (actual routes). If your component needs others, you just can get then by names (precisely: by Clojure keywords).

To start the system you must fire a REPL - interactive environment running within context of your application:

lein repl

After seeing prompt type (go). Application should start, you can visit http://localhost:3000 to see some example page.

A huge benefit of using component approach is that you get fully reloadable application. When you change literally anything - configuration, endpoints, implementation, you can just type (reset) in REPL and your application is up-to-date with the code. It’s a feature of the language, no JRebel, Spring-reloaded needed.

Adding REST endpoint

Ok, in the next step let’s add some basic REST endpoint returning JSON. We need to add 2 dependencies in project.clj file:

:dependencies
 ...
  [ring/ring-json "0.3.1"]
  [cheshire "5.1.1"]

Ring-json adds support for JSON for your routes (in ring it’s called middleware) and cheshire is Clojure JSON parser (like Jackson in Java). Modifying project dependencies if one of the few tasks that require restarting the REPL, so hit CTRL-C and type lein repl again.

To configure JSON middleware we have to add wrap-json-body and wrap-json-response just before wrap-defaults in system.clj:

(:require 
 ...
 [ring.middleware.json :refer [wrap-json-body wrap-json-response]])

(def base-config
   {:app {:middleware [[wrap-not-found :not-found]
                      [wrap-json-body {:keywords? true}]
                      [wrap-json-response]
                      [wrap-defaults :defaults]]

And finally, in endpoint/example.clj we must add some route with JSON response:

(:require 
 ...
 [ring.util.response :refer [response]]))

(defn example-endpoint [config]
  (routes
    (GET "/hello" [] (response {:hello "world"}))
    ...

Reload app with (reset) in REPL and test new route with curl:

curl -v http://localhost:3000/hello

< HTTP/1.1 200 OK
< Date: Tue, 15 Sep 2015 21:17:37 GMT
< Content-Type: application/json; charset=utf-8
< Set-Cookie: ring-session=37c337fb-6bbc-4e65-a060-1997718d03e0;Path=/;HttpOnly
< X-XSS-Protection: 1; mode=block
< X-Frame-Options: SAMEORIGIN
< X-Content-Type-Options: nosniff
< Content-Length: 151
* Server Jetty(9.2.10.v20150310) is not blacklisted
< Server: Jetty(9.2.10.v20150310)
<
* Connection #0 to host localhost left intact
{"hello": "world"}

It works! In case of any problems you can find working version in this commit.

Adding frontend with figwheel

Coding backend in Clojure is great, but what about the frontend? As you may already know, Clojure could be compiled not only to JVM bytecode, but also to Javascript. This may sound familiar if you used e.g. Coffescript. But ClojureScript philosophy is not only to provide some syntax sugar, but improve your development cycle with great tooling and fully interactive development. Let’s see how to achieve it.

The best way to introduce ClojureScript to a project is figweel. First let’s add fighweel plugin and configuration to project.clj:

:plugins
   ...
   [lein-figwheel "0.3.9"]

And cljsbuild configuration:

:cljsbuild
    {:builds [{:id "dev"
               :source-paths ["src-cljs"]
               :figwheel true
               :compiler {:main       "clojure-web-app.core"
                          :asset-path "js/out"
                          :output-to  "resources/public/js/clojure-web-app.js"
                          :output-dir "resources/public/js/out"}}]}

In short this tells ClojureScript compiler to take sources from src-cljs with figweel support and but resulting JavaScript into resources/public/js/clojure-web-app.js file. So we need to include this file in a simple HTML page:

<!DOCTYPE html>
<head>
</head>
<body>
  <div id="main">
  </div>
  <script src="js/clojure-web-app.js" type="text/javascript"></script>
</body>
</html>

To serve this static file we need to change some defaults and add corresponding route. In system.clj change api-defaults to site-defaults both in require section and base-config function. In example.clj add following route:

(GET "/" [] (io/resource "public/index.html")

Again (reset) in REPL window should reload everything.

But where is our ClojureScript source file? Let’s create file core.cljs in src-cljs/clojure-web-app directory:

(ns ^:figwheel-always clojure-web-app.core)

(enable-console-print!)

(println "hello from clojurescript")

Open another terminal and run lein fighweel. It should compile ClojureScript and print ‘Prompt will show when figwheel connects to your application’. Open http://localhost:3000. Fighweel window should prompt:

To quit, type: :cljs/quit
cljs.user=>

Type (js/alert "hello"). Boom! If everything worked you should see and alert in your browser. Open developers console in your browser. You should see hello from clojurescript printed on the console. Change it in core.cljs to (println "fighweel rocks") and save the file. Without reloading the page your should see updated message. Figweel rocks! Again, in case of any problems, refer to this commit.

In the next post I’ll show how to fetch data from MongoDB, serve it with REST to the broser and write ReactJs/Om components to render it. Stay tuned!