Clojure Ring：如何在字符串旁边打印变量

Question

我正在尝试将环境变量powered_by设置为变量message。然后我要测试message是否为空或为空。然后打印“Powered by”消息。

当前，下面的代码不起作用。

(ns helloworld.web 
    (:use compojure.core [ring.adapter.jetty :only [run-jetty]] )
    (:require [compojure.route :as route]
              [compojure.handler :as handler]))


(defroutes main-routes
  ; what's going on
    (def message (System/getenv "POWERED_BY"))
    (GET "/" [] (apply str "Powered by " message))
    (route/resources "/")
    (route/not-found "Page not found")   )


(def app
    (handler/api main-routes))

(defn -main [port]
    (run-jetty app {:port (Integer. port)}))

Answer 1

定义消息外部路由定义：

 (def message (System/getenv "POWERED_BY"))

 (defroutes main-routes
  ; what's going on
 (GET "/" [] (str "Powered by " message)
 (route/resources "/")
 (route/not-found "Page not found"))

如果您希望在每次收到请求时检索系统环境变量值，您可以使用let表单：

 (defroutes main-routes
  ; what's going on
 (GET "/" [] (let [message (System/getenv "POWERED_BY")]
                (str "Powered by " message))
 (route/resources "/")
 (route/not-found "Page not found"))

对于concat，只需使用(str arg1 arg2...），apply对列表有效，因此如果您想使用它，则应该执行类似(applystr[“powered by”message])的操作。