java/src/main/com/google/appengine/api/datastore/PostOpFuture.java

   1 // Copyright 2011 Google Inc. All Rights Reserved.
   2 package com.google.appengine.api.datastore;
   3
   4 import com.google.appengine.api.utils.FutureWrapper;
   5
   6 import java.util.concurrent.Future;
   7
   8 /**
   9  * An abstract {@link FutureWrapper} implementation that invokes callbacks
  10  * before returning its value.  The base class ensures that callbacks only run
  11  * once.
  12  *
  13  * @param <T> The type of Future.
  14  *
  15  */
  16 abstract class PostOpFuture<T> extends FutureWrapper<T, T> {
  17
  18   final DatastoreCallbacks datastoreCallbacks;
  19
  20   PostOpFuture(Future<T> delegate, DatastoreCallbacks datastoreCallbacks) {
  21     super(delegate);
  22     this.datastoreCallbacks = datastoreCallbacks;
  23   }
  24
  25   @Override
  26   protected final T wrap(T result) {
  27     executeCallbacks(result);
  28     return result;
  29   }
  30
  31   @Override
  32   protected final Throwable convertException(Throwable cause) {
  33     return cause;
  34   }
  35
  36   /**
  37    * Responsible for actual execution of the callbacks.
  38    */
  39   abstract void executeCallbacks(T result);
  40 }