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 *      https://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 */
017
018package org.apache.commons.collections4;
019
020import java.util.ArrayList;
021import java.util.Collection;
022import java.util.HashSet;
023import java.util.List;
024import java.util.Set;
025
026import org.apache.commons.collections4.bag.HashBag;
027import org.apache.commons.collections4.multimap.ArrayListValuedHashMap;
028import org.apache.commons.collections4.multimap.HashSetValuedHashMap;
029import org.apache.commons.collections4.multimap.TransformedMultiValuedMap;
030import org.apache.commons.collections4.multimap.UnmodifiableMultiValuedMap;
031import org.apache.commons.collections4.multiset.HashMultiSet;
032
033/**
034 * Provides utility methods and decorators for {@link MultiValuedMap} instances.
035 * <p>
036 * It contains various type safe and null safe methods. Additionally, it provides the following decorators:
037 * </p>
038 * <ul>
039 * <li>{@link #unmodifiableMultiValuedMap(MultiValuedMap)}</li>
040 * <li>{@link #transformedMultiValuedMap(MultiValuedMap, Transformer, Transformer)}</li>
041 * </ul>
042 *
043 * @since 4.1
044 */
045public class MultiMapUtils {
046
047    /**
048     * An empty {@link UnmodifiableMultiValuedMap}.
049     */
050    @SuppressWarnings({ "rawtypes" })
051    public static final MultiValuedMap EMPTY_MULTI_VALUED_MAP = UnmodifiableMultiValuedMap.unmodifiableMultiValuedMap(new ArrayListValuedHashMap(0, 0));
052
053    /**
054     * Returns an immutable empty {@code MultiValuedMap} if the argument is {@code null}, or the argument itself otherwise.
055     *
056     * @param <K> The type of key in the map.
057     * @param <V> The type of value in the map.
058     * @param map The map, may be null.
059     * @return An empty {@link MultiValuedMap} if the argument is null.
060     */
061    @SuppressWarnings("unchecked")
062    public static <K, V> MultiValuedMap<K, V> emptyIfNull(final MultiValuedMap<K, V> map) {
063        return map == null ? EMPTY_MULTI_VALUED_MAP : map;
064    }
065
066    /**
067     * Returns immutable EMPTY_MULTI_VALUED_MAP with generic type safety.
068     *
069     * @param <K> The type of key in the map.
070     * @param <V> The type of value in the map.
071     * @return immutable and empty {@code MultiValuedMap}.
072     */
073    @SuppressWarnings("unchecked")
074    public static <K, V> MultiValuedMap<K, V> emptyMultiValuedMap() {
075        return EMPTY_MULTI_VALUED_MAP;
076    }
077    // Null safe methods
078
079    /**
080     * Gets a Collection from {@code MultiValuedMap} in a null-safe manner.
081     *
082     * @param <K> The key type.
083     * @param <V> The value type.
084     * @param map The {@link MultiValuedMap} to use.
085     * @param key The key to look up.
086     * @return The Collection in the {@link MultiValuedMap}, or null if input map is null.
087     */
088    public static <K, V> Collection<V> getCollection(final MultiValuedMap<K, V> map, final K key) {
089        return map != null ? map.get(key) : null;
090    }
091
092    /**
093     * Gets a Bag from {@code MultiValuedMap} in a null-safe manner.
094     *
095     * @param <K> The key type.
096     * @param <V> The value type.
097     * @param map The {@link MultiValuedMap} to use.
098     * @param key The key to look up.
099     * @return A new Bag containing the values from the {@link MultiValuedMap}, or null if input map is null.
100     * @deprecated Since 4.6.0, use {@link #getValuesAsMultiSet(MultiValuedMap, Object)} instead.
101     */
102    @Deprecated
103    public static <K, V> Bag<V> getValuesAsBag(final MultiValuedMap<K, V> map, final K key) {
104        return map != null ? new HashBag<>(map.get(key)) : null;
105    }
106
107    /**
108     * Gets a List from {@code MultiValuedMap} in a null-safe manner.
109     *
110     * @param <K> The key type.
111     * @param <V> The value type.
112     * @param map The {@link MultiValuedMap} to use.
113     * @param key The key to look up.
114     * @return A new List containing the values from the {@link MultiValuedMap}, or null if input map is null.
115     */
116    public static <K, V> List<V> getValuesAsList(final MultiValuedMap<K, V> map, final K key) {
117        return map != null ? new ArrayList<>(map.get(key)) : null;
118    }
119
120    /**
121     * Gets a MultiSet from {@code MultiValuedMap} in a null-safe manner.
122     *
123     * @param <K> The key type.
124     * @param <V> The value type.
125     * @param map The {@link MultiValuedMap} to use.
126     * @param key The key to look up.
127     * @return A new MultiSet containing the values from the {@link MultiValuedMap}, or null if input map is null.
128     * @since 4.6.0
129     */
130    public static <K, V> MultiSet<V> getValuesAsMultiSet(final MultiValuedMap<K, V> map, final K key) {
131        return map != null ? new HashMultiSet<>(map.get(key)) : null;
132    }
133
134    /**
135     * Gets a Set from {@code MultiValuedMap} in a null-safe manner.
136     *
137     * @param <K> The key type.
138     * @param <V> The value type.
139     * @param map The {@link MultiValuedMap} to use.
140     * @param key The key to look up.
141     * @return A new Set containing the values from the {@link MultiValuedMap}, or null if input map is null.
142     */
143    public static <K, V> Set<V> getValuesAsSet(final MultiValuedMap<K, V> map, final K key) {
144        return map != null ? new HashSet<>(map.get(key)) : null;
145    }
146
147    /**
148     * Inverts the mappings from an input MultiValuedMap by adding entries to an output MultiValuedMap. The input is unchanged.
149     * <p>
150     * Use this method to have complete control of the output MultiValuedMap or when merging several inverse mappings. In simple cases, consider using
151     * {@link MultiValuedMap#inverted()} method.
152     * </p>
153     *
154     * @param <K>    the input <em>value</em> type and output <em>key</em> type.
155     * @param <V>    the input <em>key</em> type and output <em>value</em> type.
156     * @param <M>    the output MultiValuedMap type where {@code K} is the <em>key</em> type and {@code V} is the <em>value</em> type.
157     * @param input  The input key-value mappings of type {@code <V, K>}.
158     * @param output The output value-key mappings of type {@code <K, V>}.
159     * @return The updated output MultiValuedMap of type {@code <K, V>}
160     * @see MultiValuedMap#inverted()
161     * @since 4.6.0
162     */
163    public static <K, V, M extends MultiValuedMap<K, V>> M invert(final MultiValuedMap<? extends V, ? extends K> input, final M output) {
164        input.entries().forEach(e -> output.put(e.getValue(), e.getKey()));
165        return output;
166    }
167
168    /**
169     * Null-safe check if the specified {@code MultiValuedMap} is empty.
170     * <p>
171     * If the provided map is null, returns true.
172     * </p>
173     *
174     * @param map The map to check, may be null.
175     * @return true if the map is empty or null.
176     */
177    public static boolean isEmpty(final MultiValuedMap<?, ?> map) {
178        return map == null || map.isEmpty();
179    }
180
181    /**
182     * Creates a {@link ListValuedMap} with an {@link ArrayList ArrayList} as collection class to store the values mapped to a key.
183     *
184     * @param <K> The key type.
185     * @param <V> The value type.
186     * @return A new {@code ListValuedMap}.
187     */
188    public static <K, V> ListValuedMap<K, V> newListValuedHashMap() {
189        return new ArrayListValuedHashMap<>();
190    }
191
192    /**
193     * Creates a {@link SetValuedMap} with an {@link HashSet HashSet} as collection class to store the values mapped to a key.
194     *
195     * @param <K> The key type.
196     * @param <V> The value type.
197     * @return A new {@link SetValuedMap}.
198     */
199    public static <K, V> SetValuedMap<K, V> newSetValuedHashMap() {
200        return new HashSetValuedHashMap<>();
201    }
202
203    /**
204     * Returns a {@code TransformedMultiValuedMap} backed by the given map.
205     * <p>
206     * This method returns a new {@code MultiValuedMap} (decorating the specified map) that will transform any new entries added to it. Existing entries in the
207     * specified map will not be transformed. If you want that behavior, see {@link TransformedMultiValuedMap#transformedMap}.
208     * </p>
209     * <p>
210     * Each object is passed through the transformers as it is added to the Map. It is important not to use the original map after invoking this method, as it
211     * is a back door for adding untransformed objects.
212     * </p>
213     * <p>
214     * If there are any elements already in the map being decorated, they are NOT transformed.
215     * </p>
216     *
217     * @param <K>              the key type.
218     * @param <V>              the value type.
219     * @param map              The {@link MultiValuedMap} to transform, must not be null, typically empty.
220     * @param keyTransformer   The transformer for the map keys, null means no transformation.
221     * @param valueTransformer The transformer for the map values, null means no transformation.
222     * @return A transformed {@code MultiValuedMap} backed by the given map.
223     * @throws NullPointerException if map is null.
224     */
225    public static <K, V> MultiValuedMap<K, V> transformedMultiValuedMap(final MultiValuedMap<K, V> map,
226            final Transformer<? super K, ? extends K> keyTransformer, final Transformer<? super V, ? extends V> valueTransformer) {
227        return TransformedMultiValuedMap.transformingMap(map, keyTransformer, valueTransformer);
228    }
229
230    /**
231     * Returns an {@code UnmodifiableMultiValuedMap} backed by the given map.
232     *
233     * @param <K> The key type.
234     * @param <V> The value type.
235     * @param map The {@link MultiValuedMap} to decorate, must not be null.
236     * @return An unmodifiable {@link MultiValuedMap} backed by the provided map.
237     * @throws NullPointerException if map is null.
238     */
239    public static <K, V> MultiValuedMap<K, V> unmodifiableMultiValuedMap(final MultiValuedMap<? extends K, ? extends V> map) {
240        return UnmodifiableMultiValuedMap.<K, V>unmodifiableMultiValuedMap(map);
241    }
242
243    /**
244     * Don't allow instances.
245     */
246    private MultiMapUtils() {
247        // empty
248    }
249}