Slides for a talk given at the first China Clojure Users meeting.

1. Clojure Web
Development
OnyCloud
江宏

2. 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

3. Demo

4. Architecture
MongoDB
(Log &
Cache)
JavaScript HTTP
JSON
App Server
(Backbone.js) (Clojure)
PostgresQL

5. HTTP Server Structure
Ring Middleware Handlers
The Compojure Framework

6. 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

7. Handlers
Request in, response out.
(defn say-hello [req]
(let [name (-> req :params :name)]
{:status 200
:body (str “Hello ” name “!”)}

8. 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."}))))

9. Testing
Unit testing with clojure.test and
clojure.contrib.mock
Integration testing using Watir
Demo

10. Performance
No optimization tricks (type hints, transients,
etc.)
Average latency ~ 70ms
Long tail
Database performance can be improved (indices).

11. Lessons Learned
Good:
High productivity
Easy to test (dynamic binding)
Relatively easy learning curve

12. Lessons Learned
Bad:
Ugly stacktraces.
Exposes too much Java class hierarchy.
PersistentMap, PersistentStructMap,
struct_map ...
(contains? (transient #{:a}) :a)

13. Thank You