public void addCallbacks(GetOperation o) {
    GetOperation.Callback c =
        new GetCallbackWrapper(o.getKeys().size(),
            (GetOperation.Callback) o.getCallback());
    allCallbacks.add(c);
    for (String s : o.getKeys()) {
      Collection<GetOperation.Callback> cbs = callbacks.get(s);
      if (cbs == null) {
        cbs = new ArrayList<GetOperation.Callback>();
        callbacks.put(s, cbs);
      }
      cbs.add(c);
    }
  }
Proxy callback used for dispatching callbacks over optimized gets.
src/main/java/net/spy/memcached/protocol/ProxyCallback.java