code: public static void writeStringListToConfAsBase64(String key, List<String> list, Configuration
      conf) {
      Preconditions.checkNotNull(list);
      Iterator<String> iter = list.iterator();
      StringBuilder sb = new StringBuilder();
      while(iter.hasNext()) {
        byte[] bytes = Base64.encodeBase64(iter.next().getBytes(Charsets.UTF_8), false);
        sb.append(new String(bytes, Charsets.UTF_8));
        if (iter.hasNext()) {
          sb.append(',');
        }
      }
      conf.set(key, sb.toString());
    }
docs: Writes a list of strings into a configuration by base64 encoding them and separating
  them with commas
  
  @param key for the configuration
  @param list to write
  @param conf to write to