How to Run Jetty Example with Ring in Clojure
clojure, jetty, leiningen, ring
Solution
You're getting this error because the purpose of `lein run` (according to `lein help run`) is to "Run the project's -main function." You don't have a `-main` function in your `ws-example.web` namespace, nor do you have a `:main` specified in your `project.clj` file, which is what `lein run` is complaining about.
To fix this, you have a few options. You could move the `run-jetty` code to a new `-main` function of the `ws-example.web` function and then say `lein run -m ws-example.web`. Or you could do that and also add a line `:main ws-example.web` to `project.clj` and then just say `lein run`. Or you could try using the `lein exec` plugin to execute a file, rather than a namespace.
For more info, check out the Leiningen Tutorial.
Problem
I am following along with this example on creating a simple web service in Clojure using ring and jetty. I have this in my project.clj: ``` (defproject ws-example "0.0.1" :description "REST datastore interface." :dependencies [[org.clojure/clojure "1.5.1"] [ring/ring-jetty-adapter "0.2.5"] [ring-json-params "0.1.0"] [compojure "0.4.0"] [clj-json "0.5.3"]] :dev-dependencies [[lein-run "1.0.0-SNAPSHOT"]]) ``` This in script/run.clj ``` (use 'ring.adapter.jetty) (require '[ws-example.web :as web]) (run-jetty #'web/app {:port 8080}) ``` And this in src/ws_example/web.clj ``` (ns ws-example.web (:use compojure.core) (:use ring.middleware.json-params) (:require [clj-json.core :as json])) (defn json-response [data & [status]] {:status (or status 200) :headers {"Content-Type" "application/json"} :body (json/generate-string data)}) (defroutes handler (GET "/" [] (json-response {"hello" "world"})) (PUT "/" [name] (json-response {"hello" name}))) (def app (-> handler wrap-json-params)) ``` However, when I execute: ``` lein run script/run.clj ``` I get this error: ``` No :main namespace specified in project.clj. ``` Why am I getting this and how do I fix it?