Source code

001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4;
018
019import java.util.ArrayList;
020import java.util.Collection;
021import java.util.HashSet;
022import java.util.List;
023import java.util.Set;
024
025import org.apache.commons.collections4.bag.HashBag;
026import org.apache.commons.collections4.multimap.ArrayListValuedHashMap;
027import org.apache.commons.collections4.multimap.HashSetValuedHashMap;
028import org.apache.commons.collections4.multimap.TransformedMultiValuedMap;
029import org.apache.commons.collections4.multimap.UnmodifiableMultiValuedMap;
030
031/**
032 * Provides utility methods and decorators for {@link MultiValuedMap} instances.
033 * <p>
034 * It contains various type safe and null safe methods. Additionally, it provides
035 * the following decorators:
036 * </p>
037 * <ul>
038 *   <li>{@link #unmodifiableMultiValuedMap(MultiValuedMap)}</li>
039 *   <li>{@link #transformedMultiValuedMap(MultiValuedMap, Transformer, Transformer)}</li>
040 * </ul>
041 *
042 * @since 4.1
043 */
044public class MultiMapUtils {
045
046    /**
047     * An empty {@link UnmodifiableMultiValuedMap}.
048     */
049    @SuppressWarnings({ "rawtypes", "unchecked" })
050    public static final MultiValuedMap EMPTY_MULTI_VALUED_MAP =
051            UnmodifiableMultiValuedMap.unmodifiableMultiValuedMap(new ArrayListValuedHashMap(0, 0));
052
053    /**
054     * Returns an immutable empty {@code MultiValuedMap} if the argument is
055     * {@code null}, or the argument itself otherwise.
056     *
057     * @param <K> the type of key in the map
058     * @param <V> the type of value in the map
059     * @param map  the map, may be null
060     * @return an empty {@link MultiValuedMap} if the argument is null
061     */
062    @SuppressWarnings("unchecked")
063    public static <K, V> MultiValuedMap<K, V> emptyIfNull(final MultiValuedMap<K, V> map) {
064        return map == null ? EMPTY_MULTI_VALUED_MAP : map;
065    }
066
067    /**
068     * Returns immutable EMPTY_MULTI_VALUED_MAP with generic type safety.
069     *
070     * @param <K> the type of key in the map
071     * @param <V> the type of value in the map
072     * @return immutable and empty {@code MultiValuedMap}
073     */
074    @SuppressWarnings("unchecked")
075    public static <K, V> MultiValuedMap<K, V> emptyMultiValuedMap() {
076        return EMPTY_MULTI_VALUED_MAP;
077    }
078
079    // Null safe methods
080
081    /**
082     * Gets a Collection from {@code MultiValuedMap} in a null-safe manner.
083     *
084     * @param <K> the key type
085     * @param <V> the value type
086     * @param map  the {@link MultiValuedMap} to use
087     * @param key  the key to look up
088     * @return the Collection in the {@link MultiValuedMap}, or null if input map is null
089     */
090    public static <K, V> Collection<V> getCollection(final MultiValuedMap<K, V> map, final K key) {
091        if (map != null) {
092            return map.get(key);
093        }
094        return null;
095    }
096
097    /**
098     * Gets a Bag from {@code MultiValuedMap} in a null-safe manner.
099     *
100     * @param <K> the key type
101     * @param <V> the value type
102     * @param map  the {@link MultiValuedMap} to use
103     * @param key  the key to look up
104     * @return the Collection in the {@link MultiValuedMap} as Bag, or null if input map is null
105     */
106    public static <K, V> Bag<V> getValuesAsBag(final MultiValuedMap<K, V> map, final K key) {
107        if (map != null) {
108            final Collection<V> col = map.get(key);
109            if (col instanceof Bag) {
110                return (Bag<V>) col;
111            }
112            return new HashBag<>(col);
113        }
114        return null;
115    }
116
117    /**
118     * Gets a List from {@code MultiValuedMap} in a null-safe manner.
119     *
120     * @param <K> the key type
121     * @param <V> the value type
122     * @param map  the {@link MultiValuedMap} to use
123     * @param key  the key to look up
124     * @return the Collection in the {@link MultiValuedMap} as List, or null if input map is null
125     */
126    public static <K, V> List<V> getValuesAsList(final MultiValuedMap<K, V> map, final K key) {
127        if (map != null) {
128            final Collection<V> col = map.get(key);
129            if (col instanceof List) {
130                return (List<V>) col;
131            }
132            return new ArrayList<>(col);
133        }
134        return null;
135    }
136
137    // TODO: review the getValuesAsXXX methods - depending on the actual MultiValuedMap type, changes
138    // to the returned collection might update the backing map. This should be clarified and/or prevented.
139
140    /**
141     * Gets a Set from {@code MultiValuedMap} in a null-safe manner.
142     *
143     * @param <K> the key type
144     * @param <V> the value type
145     * @param map  the {@link MultiValuedMap} to use
146     * @param key  the key to look up
147     * @return the Collection in the {@link MultiValuedMap} as Set, or null if input map is null
148     */
149    public static <K, V> Set<V> getValuesAsSet(final MultiValuedMap<K, V> map, final K key) {
150        if (map != null) {
151            final Collection<V> col = map.get(key);
152            if (col instanceof Set) {
153                return (Set<V>) col;
154            }
155            return new HashSet<>(col);
156        }
157        return null;
158    }
159
160    /**
161     * Null-safe check if the specified {@code MultiValuedMap} is empty.
162     * <p>
163     * If the provided map is null, returns true.
164     *
165     * @param map  the map to check, may be null
166     * @return true if the map is empty or null
167     */
168    public static boolean isEmpty(final MultiValuedMap<?, ?> map) {
169        return map == null || map.isEmpty();
170    }
171
172    /**
173     * Creates a {@link ListValuedMap} with an {@link java.util.ArrayList ArrayList} as
174     * collection class to store the values mapped to a key.
175     *
176     * @param <K> the key type
177     * @param <V> the value type
178     * @return a new {@code ListValuedMap}
179     */
180    public static <K, V> ListValuedMap<K, V> newListValuedHashMap() {
181        return new ArrayListValuedHashMap<>();
182    }
183
184    /**
185     * Creates a {@link SetValuedMap} with an {@link java.util.HashSet HashSet} as
186     * collection class to store the values mapped to a key.
187     *
188     * @param <K> the key type
189     * @param <V> the value type
190     * @return a new {@link SetValuedMap}
191     */
192    public static <K, V> SetValuedMap<K, V> newSetValuedHashMap() {
193        return new HashSetValuedHashMap<>();
194    }
195
196    /**
197     * Returns a {@code TransformedMultiValuedMap} backed by the given map.
198     * <p>
199     * This method returns a new {@code MultiValuedMap} (decorating the
200     * specified map) that will transform any new entries added to it. Existing
201     * entries in the specified map will not be transformed. If you want that
202     * behavior, see {@link TransformedMultiValuedMap#transformedMap}.
203     * <p>
204     * Each object is passed through the transformers as it is added to the Map.
205     * It is important not to use the original map after invoking this method,
206     * as it is a back door for adding untransformed objects.
207     * <p>
208     * If there are any elements already in the map being decorated, they are
209     * NOT transformed.
210     *
211     * @param <K> the key type
212     * @param <V> the value type
213     * @param map  the {@link MultiValuedMap} to transform, must not be null, typically empty
214     * @param keyTransformer  the transformer for the map keys, null means no transformation
215     * @param valueTransformer  the transformer for the map values, null means no transformation
216     * @return a transformed {@code MultiValuedMap} backed by the given map
217     * @throws NullPointerException if map is null
218     */
219    public static <K, V> MultiValuedMap<K, V> transformedMultiValuedMap(final MultiValuedMap<K, V> map,
220            final Transformer<? super K, ? extends K> keyTransformer,
221            final Transformer<? super V, ? extends V> valueTransformer) {
222        return TransformedMultiValuedMap.transformingMap(map, keyTransformer, valueTransformer);
223    }
224
225    /**
226     * Returns an {@code UnmodifiableMultiValuedMap} backed by the given
227     * map.
228     *
229     * @param <K> the key type
230     * @param <V> the value type
231     * @param map  the {@link MultiValuedMap} to decorate, must not be null
232     * @return an unmodifiable {@link MultiValuedMap} backed by the provided map
233     * @throws NullPointerException if map is null
234     */
235    public static <K, V> MultiValuedMap<K, V> unmodifiableMultiValuedMap(
236            final MultiValuedMap<? extends K, ? extends V> map) {
237        return UnmodifiableMultiValuedMap.<K, V>unmodifiableMultiValuedMap(map);
238    }
239
240    /**
241     * Don't allow instances.
242     */
243    private MultiMapUtils() {
244        // empty
245    }
246
247}