001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.cache;
018
019import com.google.common.annotations.Beta;
020import com.google.common.collect.ImmutableMap;
021import com.google.common.collect.Maps;
022import com.google.common.util.concurrent.UncheckedExecutionException;
023
024import java.util.Map;
025import java.util.concurrent.Callable;
026import java.util.concurrent.ExecutionException;
027
028/**
029 * This class provides a skeletal implementation of the {@code Cache} interface to minimize the
030 * effort required to implement this interface.
031 *
032 * <p>To implement a cache, the programmer needs only to extend this class and provide an
033 * implementation for the {@link #get(Object)} and {@link #getIfPresent} methods.
034 * {@link #getUnchecked}, {@link #get(Object, Callable)}, and {@link #getAll} are implemented in
035 * terms of {@code get}; {@link #getAllPresent} is implemented in terms of {@code getIfPresent};
036 * {@link #putAll} is implemented in terms of {@link #put}, {@link #invalidateAll(Iterable)} is
037 * implemented in terms of {@link #invalidate}. The method {@link #cleanUp} is a no-op. All other
038 * methods throw an {@link UnsupportedOperationException}.
039 *
040 * @author Charles Fry
041 * @since 11.0
042 */
043@Beta
044public abstract class AbstractLoadingCache<K, V>
045    extends AbstractCache<K, V> implements LoadingCache<K, V> {
046
047  /** Constructor for use by subclasses. */
048  protected AbstractLoadingCache() {}
049
050  @Override
051  public V getUnchecked(K key) {
052    try {
053      return get(key);
054    } catch (ExecutionException e) {
055      throw new UncheckedExecutionException(e.getCause());
056    }
057  }
058
059  @Override
060  public ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
061    Map<K, V> result = Maps.newLinkedHashMap();
062    for (K key : keys) {
063      if (!result.containsKey(key)) {
064        result.put(key, get(key));
065      }
066    }
067    return ImmutableMap.copyOf(result);
068  }
069
070  @Override
071  public final V apply(K key) {
072    return getUnchecked(key);
073  }
074
075  @Override
076  public void refresh(K key) {
077    throw new UnsupportedOperationException();
078  }
079}