code: public static void save(String key, Object object) throws Exception {
          String json = new Gson().toJson(object);
          cache.put(key, json);
      }
docs: Put an object into Reservoir with the given key. This a blocking IO operation. Previously
  stored object with the same
  key (if any) will be overwritten.
  
  @param key    the key string.
  @param object the object to be stored.