CAPTCHA画像を予め作りおいていて、一定数以下になったら自動的に作り足します。ガラケーなどreCAPTCHAが使えないアプリにもCAPTCHAの機能を追加するための仕組みです。

core.clj

(ns captcha-supplier.core
  (:gen-class)
  (:require [clojure.java.io :as io])
  (:import [com.google.code.kaptcha.util Config]
           [java.util Properties]
           [javax.imageio ImageIO]
           [java.nio.file WatchService])
  (:use [nio2.io :only [path]]
        [nio2.watch :only [watch-seq]]))
 
(def ^:const available-chars "abcdefghijklmnopqrstuvwxyz0123456789")
 
(defn create-captchas [image-dir n]
  (dotimes [i n]
    (let [props (Properties.)
          config (Config. props)
          producer (.getProducerImpl config)
          rand-text (clojure.string/join (for [x (range 0 8)] (rand-nth available-chars)))
          image-file (io/file image-dir (str rand-text ".jpg"))]
      (with-open [out (io/output-stream image-file)]
        (ImageIO/write (.createImage producer rand-text)
                       "jpg" out)))))
 
(defn- supply-captcha! [image-dir threshold]
  (when (< (count (.listFiles image-dir)) threshold)
    (create-captchas image-dir 100)))
 
(defn -main [& args]
  (let [image-dir (io/file "captchas")]
    (when-not (.exists image-dir) (.mkdirs image-dir))
    (supply-captcha! image-dir 1)
    (doseq [ev (watch-seq (path (.getAbsolutePath image-dir)) :delete)]
      (supply-captcha! image-dir 50))))

project.clj

(defproject captcha-supplier "0.1.0"
  :dependencies [[org.clojure/clojure "1.5.1"]
                 [info.hoetzel/clj-nio2 "0.1.1"]
                 [com.github.axet/kaptcha "0.0.9"]]
  :aot :all
  :main captcha.core)