Get the code: learncompojure.clj
Compojure is a DSL for quickly creating performant web applications in Clojure with minimal effort:
(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:
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 for its performance and massive concurrency.
In compojure, each route is an HTTP method paired with a URL-matching pattern, an argument list, and a body.
(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:
(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:
(defroutes myapp
(GET "/" [] (fn [req] "Do something with req")))
Or, you can just use the request directly:
(defroutes myapp
(GET "/" req "Do something with req"))
Route patterns may include named parameters:
(defroutes myapp
(GET "/hello/:name" [name] (str "Hello " name)))
You can adjust what each parameter matches by supplying a regex:
(defroutes myapp
(GET ["/file/:name.:ext" :name #".*", :ext #".*"] [name ext]
(str "File: " name ext)))
Clojure uses 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:
(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 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:
(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
(defroutes myapp
(POST "/posts" req
(let [title (get (:params req) :title)
author (get (:params req) :author)]
(str "Title: " title ", Author: " author))))
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:
(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 "{}"}))
To serve up static files, use compojure.route.resources
.
Resources will be served from your project’s resources/
folder.
(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
To use templating with Compojure, you’ll need a template library. Here are a few:
Stencil is a Mustache template library:
(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
(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 is a Django and Jinja2-inspired templating language:
(require '[selmer.parser :refer [render-file]])
(defroutes myapp
(GET "/hello/:name" [name]
(render-file "templates/hello.html" {:name name})))
Hiccup is a library for representing HTML as Clojure code
(require '[hiccup.core :as hiccup])
(defroutes myapp
(GET "/hello/:name" [name]
(hiccup/html
[:html
[:body
[:h1 {:class "title"}
(str "Hello " name)]]])))
Markdown-clj is a Markdown implementation.
(require '[markdown.core :refer [md-to-html-string]])
(defroutes myapp
(GET "/hello/:name" [name]
(md-to-html-string "## Hello, world")))
Further reading:
Got a suggestion? A correction, perhaps? Open an Issue on the GitHub Repo, or make a pull request yourself!
Originally contributed by Adam Bard, and updated by 2 contributors.