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

   1 // Copyright 2011 Google. All Rights Reserved.
   2 package com.google.appengine.api.datastore;
   3
   4 import com.google.common.base.MoreObjects;
   5 import com.google.common.base.Preconditions;
   6 import com.google.common.collect.Iterables;
   7 import com.google.common.collect.Multimap;
   8
   9 import java.util.Collection;
  10 import java.util.Collections;
  11 import java.util.List;
  12
  13 /**
  14  * Abstract base class with a common {@link CallbackContext} implementation.
  15  *
  16  */
  17 abstract class BaseCallbackContext<T> implements CallbackContext<T> {
  18   private final CurrentTransactionProvider currentTxnProvider;
  19
  20   /**
  21    * All elements provided to the operation that triggered the callback.
  22    */
  23   private final List<T> elements;
  24
  25   /**
  26    * The index into {@link #elements} of the "current" element.
  27    */
  28   private int currentIndex;
  29
  30   /**
  31    * @param currentTxnProvider Provides the current transaction
  32    * @param elements All elements involved in the operation that triggered the
  33    * callback.
  34    */
  35   BaseCallbackContext(CurrentTransactionProvider currentTxnProvider, List<T> elements) {
  36     this.currentTxnProvider = Preconditions.checkNotNull(currentTxnProvider);
  37     this.elements = Collections.unmodifiableList(Preconditions.checkNotNull(elements));
  38   }
  39
  40   @Override
  41   public List<T> getElements() {
  42     return elements;
  43   }
  44
  45   @Override
  46   public Transaction getCurrentTransaction() {
  47     return currentTxnProvider.getCurrentTransaction(null);
  48   }
  49
  50   @Override
  51   public int getCurrentIndex() {
  52     return currentIndex;
  53   }
  54
  55   @Override
  56   public T getCurrentElement() {
  57     return elements.get(currentIndex);
  58   }
  59
  60   /**
  61    * Executes all appropriate callbacks for the elements in this context.
  62    *
  63    * @param callbacksByKind A Multimap containing lists of callbacks, organized by
  64    * kind.
  65    * @param noKindCallbacks Callbacks that apply to all elements, independent
  66    * of kind.
  67    *
  68    * @throws IllegalStateException If this method has already been called.
  69    */
  70   void executeCallbacks(Multimap<String, DatastoreCallbacksImpl.Callback> callbacksByKind,
  71       Collection<DatastoreCallbacksImpl.Callback> noKindCallbacks) {
  72     Preconditions.checkState(currentIndex == 0,
  73         "executeCallbacks cannot be called more than once.");
  74     for (T ele : elements) {
  75       Iterable<DatastoreCallbacksImpl.Callback> allCallbacksToRun =
  76           Iterables.concat(callbacksByKind.get(getKind(ele)), noKindCallbacks);
  77       for (DatastoreCallbacksImpl.Callback callback : allCallbacksToRun) {
  78         callback.run(this);
  79       }
  80       currentIndex++;
  81     }
  82   }
  83
  84   /**
  85    * Abstract method that, given an element, knows how to extract its kind.
  86    */
  87   abstract String getKind(T ele);
  88
  89   @Override
  90   public String toString() {
  91     return MoreObjects.toStringHelper(this)
  92         .add("elements", elements)
  93         .add("currentIndex", currentIndex)
  94         .toString();
  95   }
  96 }