Web Applications in Clojure

Clojure, as a Lisp dialect running on the JVM, is a purely functional language that also takes advantage of the great library support available in the Java world.

As a functional language, it provides great abstractions for developing web applications, particularly because of how it handles HTTP, which is a fundamentally stateless protocol. In this talk, I will explain the fundamental concepts behind Clojure web applications and how the Clojure libraries harness the power of the existing Java infrastructure in order to provide state of the art server technology.

Transcript

1. Web Applications in Clojure Munich Clojurians February 7, 2017
2. Joy Clark Consultant @ innoQ joy.clark@innoq.com @iamjoyclark
3. @iamjoyclark http://upload.wikimedia.org/wikipedia/en/1/
4. @iamjoyclark Clojure > Lisp Variant for the JVM > Functional Language > Dynamically Typed > Immutable Data Structures > Simplicity - Separation of Data and Behavior
5. @iamjoyclark Data Structures “Hello World” 3 3.14 3/2 \a :first foo #“Ch.*se” (“Hello” :first) [3 4 3] { :name “Joy” :company “innoQ” } #{3 4 3}
6. @iamjoyclark Functions (+ 1 2) > 3 (:city {:name “innoQ” :city “Munich”}) > “Munich” (map inc [1 2 3]) > (2 3 4)
7. @iamjoyclark Web Applications
8. @iamjoyclark What’s a Web Application?
9. @iamjoyclark Ring https://github.com/ring-clojure/ring • HTTP Server abstraction • Request & Response are data • Web App is a function
10. @iamjoyclark Ring
11. @iamjoyclark Ring: Request {:uri “/”
 :params { :name “Joy” } :request-method :get :headers { … } …}
12. @iamjoyclark Ring: Response {:status 200 :headers { … }
 :body “Hello!”}
13. @iamjoyclark Ring: Handler (defn example-app [request] (let [name (get-in request [:params :name])] {:status 200
 :headers {“Content-Type” “text/plain”} :body (str “Hello, ” name “!”)})
14. @iamjoyclark Ring: Adapter > Jetty > Servlet > http-kit > Tomcat > …
15. @iamjoyclark Ring: Middleware (defn wrap-logging [handler] (fn [request] (print request)
 (let [response (handler request)] (print response) response))) webapp Java HTTP Server Ring Server Adapter middleware middleware
16. @iamjoyclark Ring: Middleware > https://github.com/ring-clojure/ring-defaults > https://github.com/ring-clojure/ring-json
17. @iamjoyclark Compojure https://github.com/weavejester/compojure
18. @iamjoyclark Compojure
19. @iamjoyclark Compojure: Handler (defroutes app-routes (GET “/” request (list-users request)) (POST “/” {params :params :as request} (add-user request params)) (GET “/:username” [username :as request] (get-user request username)))
20. @iamjoyclark Putting it all together
21. @iamjoyclark HTML Templating
22. @iamjoyclark Hiccup [:div {:id “foo”} [:span “bar”]] <div id=“foo”> <span>bar</span> </div> https://github.com/weavejester/hiccup
23. @iamjoyclark Hiccup (defn render-html [input] (hiccup.util/escape-html (hiccup.core/html input))) Make sure to escape HTML when using Hiccup!
24. @iamjoyclark Hiccup: Alternatives > https://github.com/cgrand/enlive > https://github.com/yogthos/Selmer
25. @iamjoyclark Summary
26. @iamjoyclark Summary > Functional Language ideal for Web Apps > Clojure usage is increasing > Libraries vs. Frameworks > Community is healthy and welcoming
27. @iamjoyclark Interesting Libraries > https://github.com/technomancy/leiningen > https://github.com/weavejester/environ > https://github.com/krisajenkins/yesql
28. @iamjoyclark “Frameworks” > https://github.com/weavejester/duct > http://www.luminusweb.net > https://github.com/otto-de/tesla-microservice > https://github.com/metosin/compojure-api
29. Joy Clark | @iamjoyclark | joy.clark@innoq.com www.innoq.com Tutorial for Getting Started: https://github.com/innoq/tutorial-clj-webapp Thank you!