Clojure Compojure Added Session Handler

handler.clj

;; block 1
(ns sessiontest.handler
  (:use [ring.middleware.json :only (wrap-json-response)]
               ;; use json response
        ring.middleware.session
               ;; use session
        [ring.util.response :only (response)]
               ;; use response
        [hiccup.middleware :only (wrap-base-url)])
               ;; use hiccup
  (:require [compojure.core :refer :all]
            [compojure.route :as route]
            [ring.middleware.defaults :refer [wrap-defaults site-defaults]]
            [compojure.handler :as handler]                 
               ;; require handler
            ))
;; block 2
(defroutes app-routes
  ;; catch the :session (keyword) into session variable
  (GET "/" {session :session} []
    ;; catch :counter (keyword) inside the session (variable) to c (variable) if exists, otherwise use 0 (zero) to fill the value
    (let [c (:counter session 0)
          ;; define the session (variable) with the old session which added :counter (keyword) inside and also increment the value
          session (assoc session :counter (inc c))]
      (-> 
          ;; return the result as json 
          (response {:the_counter (:counter session)})
          ;; re-new the session
          (assoc :session session))))
  ;; just handle when no route matched
  (route/not-found "Not Found"))
;; block 3
(def app
  (-> (handler/site
        app-routes {:session 
                      {:cookie-name "counter-session"
                       :cookie-attrs 
                         {:max-age 15 ;; expires in second 
                            }}})
      (wrap-base-url)
      (wrap-json-response)
      (wrap-session))
  ;; delete or comment this default command
  ;;(wrap-defaults app-routes site-defaults)
  )