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!

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. Coffeescript. 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 put resulting JavaScript into resources/public/js/clojure-web-app.js file. So we need to include this file in a simple HTML page:

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.

id="main">

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 figwheel. 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=>

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. Fighweel rocks! Again, in case of any problems, refer to this commit.

UPDATE: In the latest duct release, there is an +cljs option which make it possible to use reloaded repl and fighweel in a single REPL. Highly recommended!

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

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Easy configuration usage with ConfigSlurper

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DDevelopment & Design

33rd Degree day 1 review

33rd Degree is over. After the one last year, my expectations were very high, but Grzegorz Duda once again proved he's more than able to deliver. With up to five tracks (most of the time: four presentations + one workshop), and ~650 attendees,  there was a lot to see and a lot to do, thus everyone will probably have a little bit different story to tell. Here is mine.

Twitter: From Ruby on Rails to the JVM

Raffi Krikorian talking about Twitter and JVM
The conference started with  Raffi Krikorian from Twitter, talking about their use for JVM. Twitter was build with Ruby but with their performance management a lot of the backend was moved to Scala, Java and Closure. Raffi noted, that for Ruby programmers Scala was easier to grasp than Java, more natural, which is quite interesting considering how many PHP guys move to Ruby these days because of the same reasons. Perhaps the path of learning Jacek Laskowski once described (Java -> Groovy -> Scala/Closure) may be on par with PHP -> Ruby -> Scala. It definitely feels like Scala is the holy grail of languages these days.

Raffi also noted, that while JVM delivered speed and a concurrency model to Twitter stack, it wasn't enough, and they've build/customized their own Garbage Collector. My guess is that Scala/Closure could also be used because of a nice concurrency solutions (STM, immutables and so on).

Raffi pointed out, that with the scale of Twitter, you easily get 3 million hits per second, and that means you probably have 3 edge cases every second. I'd love to learn listen to lessons they've learned from this.

 

Complexity of Complexity


The second keynote of the first day, was Ken Sipe talking about complexity. He made a good point that there is a difference between complex and complicated, and that we often recognize things as complex only because we are less familiar with them. This goes more interesting the moment you realize that the shift in last 20 years of computer languages, from the "Less is more" paradigm (think Java, ASM) to "More is better" (Groovy/Scala/Closure), where you have more complex language, with more powerful and less verbose syntax, that is actually not more complicated, it just looks less familiar.

So while 10 years ago, I really liked Java as a general purpose language for it's small set of rules that could get you everywhere, it turned out that to do most of the real world stuff, a lot of code had to be written. The situation got better thanks to libraries/frameworks and so on, but it's just patching. New languages have a lot of stuff build into, which makes their set of rules and syntax much more complex, but once you get familiar, the real world usage is simple, faster, better, with less traps laying around, waiting for you to fall.

Ken also pointed out, that while Entity Service Bus looks really simple on diagrams, it's usually very difficult and complicated to use from the perspective of the programmer. And that's probably why it gets chosen so often - the guys selling/buying it, look no deeper than on the diagram.

 

Pointy haired bosses and pragmatic programmers: Facts and Fallacies of Software Development

Venkat Subramaniam with Dima
Dima got lucky. Or maybe not.

Venkat Subramaniam is the kind of a speaker that talk about very simple things in a way, which makes everyone either laugh or reflect. Yes, he is a showman, but hey, that's actually good, because even if you know the subject quite well, his talks are still very entertaining.
This talk was very generic (here's my thesis: the longer the title, the more generic the talk will be), interesting and fun, but at the end I'm unable to see anything new I'd have learned, apart from the distinction between Dynamic vs Static and Strong vs Weak typing, which I've seen the last year, but managed to forgot. This may be a very interesting argument for all those who are afraid of Groovy/Ruby, after bad experience with PHP or Perl.

Build Trust in Your Build to Deployment Flow!


Frederic Simon talked about DevOps and deployment, and that was a miss in my  schedule, because of two reasons. First, the talk was aimed at DevOps specifically, and while the subject is trendy lately, without big-scale problems, deployment is a process I usually set up and forget about. It just works, mostly because I only have to deal with one (current) project at a time. 
Not much love for Dart.
Second, while Frederic has a fabulous accent and a nice, loud voice, he tends to start each sentence loud and fade the sound at the end. This, together with mics failing him badly, made half of the presentation hard to grasp unless you were sitting in the first row.
I'm not saying the presentation was bad, far from it, it just clearly wasn't for me.
I've left a few minutes before the end, to see how many people came to Dart presentation by Mike West. I was kind of interested, since I'm following Warsaw Google Technology User Group and heard a few voices about why I should pay attentions to that new Google language. As you can see from the picture on the right, the majority tends to disagree with that opinion.

 

Non blocking, composable reactive web programming with Iteratees

Sadek Drobi's talk about Iteratees in Play 2.0 was very refreshing. Perhaps because I've never used Play before, but the presentation was flawless, with well explained problems, concepts and solutions.
Sadek started with a reflection on how much CPU we waste waiting for IO in web development, then moved to Play's Iteratees, to explain the concept and implementation, which while very different from the that overused Request/Servlet model, looked really nice and simple. I'm not sure though, how much the problem is present when you have a simple service, serving static content before your app server. Think apache (and faster) before tomcat. That won't fix the upload/download issue though, which is beautifully solved in Play 2.0

The Future of the Java Platform: Java SE 8 & Beyond


Simon Ritter is an intriguing fellow. If you take a glance at his work history (AT&T UNIX System Labs -> Novell -> Sun -> Oracle), you can easily see, he's a heavy weight player.
His presentation was rich in content, no corpo-bullshit. He started with a bit of history of JCP and how it looks like right now, then moved to the most interesting stuff, changes. Now I could give you a summary here, but there is really no point: you'd be much better taking look at the slides. There are only 48 of them, but everything is self-explanatory.
While I'm very disappointed with the speed of changes, especially when compared to the C# world, I'm glad with the direction and the fact that they finally want to BREAK the compatibility with the broken stuff (generics, etc.).  Moving to other languages I guess I won't be the one to scream "My god, finally!" somewhere in 2017, though. All the changes together look very promising, it's just that I'd like to have them like... now? Next year max, not near the heat death of the universe.

Simon also revealed one of the great mysteries of Java, to me:
The original idea behind JNI was to make it hard to write, to discourage people form using it.
On a side note, did you know Tegra3 has actually 5 cores? You use 4 of them, and then switch to the other one, when you battery gets low.

BOF: Spring and CloudFoundry


Having most of my folks moved to see "Typesafe stack 2.0" fabulously organized by Rafał Wasilewski and  Wojtek Erbetowski (with both of whom I had a pleasure to travel to the conference) and knowing it will be recorded, I've decided to see what Josh Long has to say about CloudFoundry, a subject I find very intriguing after the de facto fiasco of Google App Engine.

The audience was small but vibrant, mostly users of Amazon EC2, and while it turned out that Josh didn't have much, with pricing and details not yet public, the fact that Spring Source has already created their own competition (Could Foundry is both an Open Source app and a service), takes a lot from my anxiety.

For the review of the second day of the conference, go here.
DDevelopment & Design

Warszawa JUG z nową stroną

Warszawska Grupa Użytkowników Technologii Java (WJUG) ma nową stronę internetową. Kod i layout strony przygotował TouK i przekazał grupie. Niech służy! Cieszymy się, że mogliśmy przyczynić się w ten sposób do budowy javowej społeczności.