1/*
2 * Copyright (C) 2011 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.cache;
18
19import com.google.common.annotations.Beta;
20import com.google.common.collect.ImmutableMap;
21import com.google.common.collect.Maps;
22import com.google.common.util.concurrent.UncheckedExecutionException;
23
24import java.util.Map;
25import java.util.concurrent.Callable;
26import java.util.concurrent.ExecutionException;
27
28/**
29 * This class provides a skeletal implementation of the {@code Cache} interface to minimize the
30 * effort required to implement this interface.
31 *
32 * <p>To implement a cache, the programmer needs only to extend this class and provide an
33 * implementation for the {@link #get} and {@link #getIfPresent} methods. {@link #getUnchecked},
34 * {@link #get(K, Callable)}, and {@link #getAll} are implemented in terms of {@code get};
35 * {@link #getAllPresent} is implemented in terms of {@code get}; {@link #invalidateAll(Iterable)}
36 * is implemented in terms of {@link #invalidate}. The method {@link #cleanUp} is a no-op. All other
37 * methods throw an {@link UnsupportedOperationException}.
38 *
39 * @author Charles Fry
40 * @since 11.0
41 */
42@Beta
43public abstract class AbstractLoadingCache<K, V>
44    extends AbstractCache<K, V> implements LoadingCache<K, V> {
45
46  /** Constructor for use by subclasses. */
47  protected AbstractLoadingCache() {}
48
49  @Override
50  public V getUnchecked(K key) {
51    try {
52      return get(key);
53    } catch (ExecutionException e) {
54      throw new UncheckedExecutionException(e.getCause());
55    }
56  }
57
58  @Override
59  public ImmutableMap<K, V> getAll(Iterable<? extends K> keys) throws ExecutionException {
60    Map<K, V> result = Maps.newLinkedHashMap();
61    for (K key : keys) {
62      if (!result.containsKey(key)) {
63        result.put(key, get(key));
64      }
65    }
66    return ImmutableMap.copyOf(result);
67  }
68
69  @Override
70  public final V apply(K key) {
71    return getUnchecked(key);
72  }
73
74  @Override
75  public void refresh(K key) {
76    throw new UnsupportedOperationException();
77  }
78}
79