Temporarily redefine jvm system properties to include user-specified items

with_properties.clj

(defmacro with-properties
  "Temporarily redefine jvm system properties to include entries from `props-user`."
  [props-user & body]
  `(let [props-orig# (into {} (for [[prop-key# prop-val#] ~props-user]
                                [prop-key# (System/getProperty prop-key#)]))]
     (doseq [prop-key# (keys ~props-user)]
       (System/setProperty prop-key# (get ~props-user prop-key#)))
     (try
       ~@body
       (finally
         (doseq [prop-key# (keys ~props-user)]
           (let [prop-val-orig# (get props-orig# prop-key#)]
             (if prop-val-orig#
               (System/setProperty prop-key# prop-val-orig#)
               (System/clearProperty prop-key#))))))))