private static String getAccept(Operation operation) {
    String accepts = null;
    String defaultContentType = "application/json";
    if (operation.getProduces() != null && !operation.getProduces().isEmpty()) {
      StringBuilder sb = new StringBuilder();
      for (String produces : operation.getProduces()) {
        if (defaultContentType.equalsIgnoreCase(produces)) {
          accepts = defaultContentType;
          break;
        } else {
          if (sb.length() > 0) {
            sb.append(",");
          }
          sb.append(produces);
        }
      }
      if (accepts == null) {
        accepts = sb.toString();
      }
    } else {
      accepts = defaultContentType;
    }

    return accepts;
  }
 private String joinStrings(String sep, List<String> ss) {
   StringBuilder sb = new StringBuilder();
   for (String s : ss) {
     if (sb.length() > 0) {
       sb.append(sep);
     }
     sb.append(s);
   }
   return sb.toString();
 }