code: public static void addCacheFile(URI uri, Configuration conf) {
      String files = conf.get("mapred.cache.files");
      conf.set("mapred.cache.files", files == null ? uri.toString() : files + ","
               + uri.toString());
    }
docs: Add a file to be localized to the conf
  @param uri The uri of the cache to be localized
  @param conf Configuration to add the cache to