scratch.clj

(defn write [name data]
  (let [buf (make-array Byte/TYPE 1024)
        dest (FileOutputStream. name)]
    (with-open [r (BufferedInputStream. data)
                w (BufferedOutputStream. dest)]
      (loop [bytes (.read r buf 0 1024)]
       (when-not (= bytes -1)
         (.write w buf 0 bytes)
         (recur (.read r buf 0 1024)))))
    (println "Wrote" name)))

(defn download [url]
  (let [idx (inc (.lastIndexOf url (int \/)))
        name (subs url idx)
        conn (.openConnection (URL. url))]
    (doto conn
      (.connect))
    (write name (.getInputStream conn))))