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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}))
```
Create a project with [Leiningen](http://leiningen.org/):
```
lein new myapp
```
Add your dependencies:
```
[compojure "1.1.8"]
[http-kit "2.1.16"]
```
And 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")))
```
Route patterns may include named parameters,
```clojure
(defroutes myapp
(GET "/hello/:name" [name] (str "Hello " name)))
```
You can match entire paths with *
```clojure
(defroutes myapp
(GET "/file/*.*" [*] (str *)))
```
Handlers may utilize query parameters:
```clojure
(defroutes myapp
(GET "/posts" []
(fn [req]
(let [title (get (:params req) "title")
author (get (:params req) "title")]
" Do something with title and author"))))
```
Or, for POST and PUT requests, form parameters
```clojure
(defroutes myapp
(POST "/posts" []
(fn [req]
(let [title (get (:params req) "title")
author (get (:params req) "title")]
"Do something with title and author"))))
```
### Return values
The return value of a route block determines at least 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 body](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:
[Clojure for the Brave and True](http://www.braveclojure.com/)
|
