public void update(String key){
    synchronized(this.cache){
      U fromCache = cache.get(key);
      if(!(fromCache == null)){
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream objOut;
        try{
          objOut = new ObjectOutputStream(baos);
          objOut.writeObject(fromCache);
          objOut.close();
          this.backing.queue.add(new KeyValAction(key, this.group, baos, KVActions.PUT));
        }catch(IOException e){
          e.printStackTrace();
        }
      }
    }
  }