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Clojure Web Development

This document discusses Clojure web development and describes a web-based project management system called Trakr that was created using Clojure. Trakr uses a MongoDB database and has a modern friendly UI. The architecture involves a Clojure HTTP server with a Ring middleware pipeline and Compojure routing to map requests to handlers. Testing is done with clojure.test and clojure.contrib.mock. Performance is around 70ms average latency.

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Clojure Web Development OnyCloud 江宏
Example - Trakr https://trakrapp.com/ Web-based project management system A product created for our own needs Requirements Feature-complete for software devs Modern friendly UI Affordable
Demo
Architecture MongoDB (Log & Cache) JavaScript HTTP JSON App Server (Backbone.js) (Clojure) PostgresQL
HTTP Server Structure Ring Middleware Handlers The Compojure Framework
Routes Mapping: Request -> Handler: (defroutes app-routes (context "/users" [] (GET "/new" [] accounts/show-signup) (POST "/" [email] (accounts/new email))) ;; GET /users/new -> accounts/show-signup ;; POST /users/ -> accounts/new
Handlers Request in, response out. (defn say-hello [req] (let [name (-> req :params :name)] {:status 200 :body (str “Hello ” name “!”)}
Middleware Transform: Handler -> New Handler (defn wrap-failsafe [handler] (fn [request] (try (handler request) (catch Exception e (.printStackTrace e) {:status 500 :body "An error occured."}))))
Testing Unit testing with clojure.test and clojure.contrib.mock Integration testing using Watir Demo
Performance No optimization tricks (type hints, transients, etc.) Average latency ~ 70ms Long tail Database performance can be improved (indices).
Lessons Learned Good: High productivity Easy to test (dynamic binding) Relatively easy learning curve
Lessons Learned Bad: Ugly stacktraces. Exposes too much Java class hierarchy. PersistentMap, PersistentStructMap, struct_map ... (contains? (transient #{:a}) :a)
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