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+---
+category: tool
+tool: compojure
+contributors:
+    - ["Adam Bard", "http://adambard.com/"]
+filename: learncompojure.clj
+---
+
+## Getting Started with Compojure
+
+Compojure is a DSL for *quickly* creating *performant* web applications
+in Clojure with minimal effort:
+
+```clojure
+(ns myapp.core
+  (:require [compojure.core :refer :all]
+            [org.httpkit.server :refer [run-server]])) ; httpkit is a server
+
+(defroutes myapp
+  (GET "/" [] "Hello World"))
+
+(defn -main []
+  (run-server myapp {:port 5000}))
+```
+
+**Step 1:** Create a project with [Leiningen](http://leiningen.org/):
+
+```
+lein new myapp
+```
+
+**Step 2:** Put the above code in `src/myapp/core.clj`
+
+**Step 3:** Add some dependencies to `project.clj`:
+
+```
+[compojure "1.1.8"]
+[http-kit "2.1.16"]
+```
+
+**Step 4:** Run:
+
+```
+lein run -m myapp.core
+```
+
+View at: <http://localhost:5000/>
+
+Compojure apps will run on any ring-compatible server, but we recommend
+[http-kit](http://http-kit.org/) for its performance and
+[massive concurrency](http://http-kit.org/600k-concurrent-connection-http-kit.html).
+
+### Routes
+
+In compojure, each route is an HTTP method paired with a URL-matching pattern,
+an argument list, and a body.
+
+```clojure
+(defroutes myapp
+  (GET "/" [] "Show something")
+  (POST "/" [] "Create something")
+  (PUT "/" [] "Replace something")
+  (PATCH "/" [] "Modify Something")
+  (DELETE "/" [] "Annihilate something")
+  (OPTIONS "/" [] "Appease something")
+  (HEAD "/" [] "Preview something"))
+```
+
+Compojure route definitions are just functions which
+[accept request maps and return response maps](https://github.com/mmcgrana/ring/blob/master/SPEC):
+
+```clojure
+(myapp {:uri "/" :request-method :post})
+; => {:status 200
+;     :headers {"Content-Type" "text/html; charset=utf-8}
+;     :body "Create Something"}
+```
+
+The body may be a function, which must accept the request as a parameter:
+
+```clojure
+(defroutes myapp
+  (GET "/" [] (fn [req] "Do something with req")))
+```
+
+Or, you can just use the request directly:
+
+```clojure
+(defroutes myapp
+  (GET "/" req "Do something with req"))
+```
+
+Route patterns may include named parameters:
+
+```clojure
+(defroutes myapp
+  (GET "/hello/:name" [name] (str "Hello " name)))
+```
+
+You can adjust what each parameter matches by supplying a regex:
+
+```clojure
+(defroutes myapp
+  (GET ["/file/:name.:ext" :name #".*", :ext #".*"] [name ext]
+    (str "File: " name ext)))
+```
+
+### Middleware
+
+Clojure uses [Ring](https://github.com/ring-clojure/ring) for routing.
+Handlers are just functions that accept a request map and return a
+response map (Compojure will turn strings into 200 responses for you).
+
+You can easily write middleware that wraps all or part of your
+application to modify requests or responses:
+
+```clojure
+(defroutes myapp
+  (GET "/" req (str "Hello World v" (:app-version req))))
+
+(defn wrap-version [handler]
+  (fn [request]
+    (handler (assoc request :app-version "1.0.1"))))
+
+(defn -main []
+  (run-server (wrap-version myapp) {:port 5000}))
+```
+
+[Ring-Defaults](https://github.com/ring-clojure/ring-defaults) provides some handy
+middlewares for sites and apis, so add it to your dependencies:
+
+```
+[ring/ring-defaults "0.1.1"]
+```
+
+Then, you can import it in your ns:
+
+```
+(ns myapp.core
+  (:require [compojure.core :refer :all]
+            [ring.middleware.defaults :refer :all]
+            [org.httpkit.server :refer [run-server]]))
+```
+
+And use `wrap-defaults` to add the `site-defaults` middleware to your
+app:
+
+```
+(defn -main []
+  (run-server (wrap-defaults myapp site-defaults) {:port 5000}))
+```
+
+Now, your handlers may utilize query parameters:
+
+```clojure
+(defroutes myapp
+  (GET "/posts" req
+    (let [title (get (:params req) "title")
+          author (get (:params req) "author")]
+      (str "Title: " title ", Author: " author))))
+```
+
+Or, for POST and PUT requests, form parameters as well
+
+```clojure
+(defroutes myapp
+  (POST "/posts" req
+    (let [title (get (:params req) "title")
+          author (get (:params req) "author")]
+      (str "Title: " title ", Author: " author))))
+```
+
+
+### Return values
+
+The return value of a route block determines the response body
+passed on to the HTTP client, or at least the next middleware in the
+ring stack. Most commonly, this is a string, as in the above examples.
+But, you may also return a [response map](https://github.com/mmcgrana/ring/blob/master/SPEC):
+
+```clojure
+(defroutes myapp
+  (GET "/" []
+    {:status 200 :body "Hello World"})
+  (GET "/is-403" []
+    {:status 403 :body ""})
+  (GET "/is-json" []
+    {:status 200 :headers {"Content-Type" "application/json"} :body "{}"}))
+```
+
+### Static Files
+
+To serve up static files, use `compojure.route.resources`.
+Resources will be served from your project's `resources/` folder.
+
+```clojure
+(require '[compojure.route :as route])
+
+(defroutes myapp
+  (GET "/")
+  (route/resources "/")) ; Serve static resources at the root path
+
+(myapp {:uri "/js/script.js" :request-method :get})
+; => Contents of resources/public/js/script.js
+```
+
+### Views / Templates
+
+To use templating with Compojure, you'll need a template library. Here are a few:
+
+#### [Stencil](https://github.com/davidsantiago/stencil)
+
+[Stencil](https://github.com/davidsantiago/stencil) is a [Mustache](http://mustache.github.com/) template library:
+
+```clojure
+(require '[stencil.core :refer [render-string]])
+
+(defroutes myapp
+  (GET "/hello/:name" [name]
+    (render-string "Hello {{name}}" {:name name})))
+```
+
+You can easily read in templates from your resources directory. Here's a helper function
+
+```clojure
+(require 'clojure.java.io)
+
+(defn read-template [filename]
+  (slurp (clojure.java.io/resource filename)))
+
+(defroutes myapp
+  (GET "/hello/:name" [name]
+    (render-string (read-template "templates/hello.html") {:name name})))
+```
+
+#### [Selmer](https://github.com/yogthos/Selmer)
+
+[Selmer](https://github.com/yogthos/Selmer) is a Django and Jinja2-inspired templating language:
+
+```clojure
+(require '[selmer.parser :refer [render-file]])
+
+(defroutes myapp
+  (GET "/hello/:name" [name]
+    (render-file "templates/hello.html" {:name name})))
+```
+
+#### [Hiccup](https://github.com/weavejester/hiccup)
+
+[Hiccup](https://github.com/weavejester/hiccup) is a library for representing HTML as Clojure code
+
+```clojure
+(require '[hiccup.core :as hiccup])
+
+(defroutes myapp
+  (GET "/hello/:name" [name]
+    (hiccup/html
+      [:html
+        [:body
+          [:h1 {:class "title"}
+            (str "Hello " name)]]])))
+```
+
+#### [Markdown](https://github.com/yogthos/markdown-clj)
+
+[Markdown-clj](https://github.com/yogthos/markdown-clj) is a Markdown implementation.
+
+```clojure
+(require '[markdown.core :refer [md-to-html-string]])
+
+(defroutes myapp
+  (GET "/hello/:name" [name]
+    (md-to-html-string "## Hello, world")))
+```
+
+Further reading:
+
+* [Official Compojure Documentation](https://github.com/weavejester/compojure/wiki)
+
+* [Clojure for the Brave and True](http://www.braveclojure.com/)