class StaticInterceptor implements Interceptor {

  @Override
  public Event intercept(Event event) {
    Map<String, String> headers = event.getHeaders();

    if (preserveExisting && headers.containsKey(key)) {
      return event;
    }

    headers.put(key, value);
    return event;
  }

  private  StaticInterceptor(boolean preserveExisting, String key,
      String value);

}