core.clj

(ns example.core
  (:require [org.httpkit.server :as http-kit]
            [compojure.api.sweet :refer :all]
            [ring.util.http-response :refer :all]
            [clojure.spec.alpha :as s]))

(def users [{:id 1 :name "Alice"}
            {:id 2 :name "Bob"}])

(def users-by-id (zipmap (map :id users) users))            

(s/def ::id int?)
(s/def ::name string?)
(s/def ::user (s/keys ::req-un [::id ::name]))

(def app
  (api
    {:coercion :spec
     :swagger {:ui "/swagger" 
               :spec "/swagger/swagger.json"}}
    (GET "/users/:id" []
      :path-params [id :- ::id]
      :return (s/nilable ::user)
      (let [user (users-by-id id)]
        (if user
          (ok user)
          (not-found (str "user " id " not found")))))))

(defonce server
  (http-kit/run-server #'app {:port 8080}))