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     * <code>MultiMapUtils</code> should not normally be instantiated.
048     */
049    private MultiMapUtils() {}
050
051    /**
052     * An empty {@link UnmodifiableMultiValuedMap}.
053     */
054    @SuppressWarnings({ "rawtypes", "unchecked" })
055    public static final MultiValuedMap EMPTY_MULTI_VALUED_MAP =
056            UnmodifiableMultiValuedMap.unmodifiableMultiValuedMap(new ArrayListValuedHashMap(0, 0));
057
058    /**
059     * Returns immutable EMPTY_MULTI_VALUED_MAP with generic type safety.
060     *
061     * @param <K> the type of key in the map
062     * @param <V> the type of value in the map
063     * @return immutable and empty <code>MultiValuedMap</code>
064     */
065    @SuppressWarnings("unchecked")
066    public static <K, V> MultiValuedMap<K, V> emptyMultiValuedMap() {
067        return EMPTY_MULTI_VALUED_MAP;
068    }
069
070    // Null safe methods
071
072    /**
073     * Returns an immutable empty <code>MultiValuedMap</code> if the argument is
074     * <code>null</code>, or the argument itself otherwise.
075     *
076     * @param <K> the type of key in the map
077     * @param <V> the type of value in the map
078     * @param map  the map, may be null
079     * @return an empty {@link MultiValuedMap} if the argument is null
080     */
081    @SuppressWarnings("unchecked")
082    public static <K, V> MultiValuedMap<K, V> emptyIfNull(final MultiValuedMap<K, V> map) {
083        return map == null ? EMPTY_MULTI_VALUED_MAP : map;
084    }
085
086    /**
087     * Null-safe check if the specified <code>MultiValuedMap</code> is empty.
088     * <p>
089     * If the provided map is null, returns true.
090     *
091     * @param map  the map to check, may be null
092     * @return true if the map is empty or null
093     */
094    public static boolean isEmpty(final MultiValuedMap<?, ?> map) {
095        return map == null || map.isEmpty();
096    }
097
098    // Null safe getters
099    // -------------------------------------------------------------------------
100
101    /**
102     * Gets a Collection from <code>MultiValuedMap</code> in a null-safe manner.
103     *
104     * @param <K> the key type
105     * @param <V> the value type
106     * @param map  the {@link MultiValuedMap} to use
107     * @param key  the key to look up
108     * @return the Collection in the {@link MultiValuedMap}, or null if input map is null
109     */
110    public static <K, V> Collection<V> getCollection(final MultiValuedMap<K, V> map, final K key) {
111        if (map != null) {
112            return map.get(key);
113        }
114        return null;
115    }
116
117    // TODO: review the getValuesAsXXX methods - depending on the actual MultiValuedMap type, changes
118    // to the returned collection might update the backing map. This should be clarified and/or prevented.
119
120    /**
121     * Gets a List from <code>MultiValuedMap</code> 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 the Collection in the {@link MultiValuedMap} as List, or null if input map is null
128     */
129    public static <K, V> List<V> getValuesAsList(final MultiValuedMap<K, V> map, final K key) {
130        if (map != null) {
131            final Collection<V> col = map.get(key);
132            if (col instanceof List) {
133                return (List<V>) col;
134            }
135            return new ArrayList<>(col);
136        }
137        return null;
138    }
139
140    /**
141     * Gets a Set from <code>MultiValuedMap</code> 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     * Gets a Bag from <code>MultiValuedMap</code> in a null-safe manner.
162     *
163     * @param <K> the key type
164     * @param <V> the value type
165     * @param map  the {@link MultiValuedMap} to use
166     * @param key  the key to look up
167     * @return the Collection in the {@link MultiValuedMap} as Bag, or null if input map is null
168     */
169    public static <K, V> Bag<V> getValuesAsBag(final MultiValuedMap<K, V> map, final K key) {
170        if (map != null) {
171            final Collection<V> col = map.get(key);
172            if (col instanceof Bag) {
173                return (Bag<V>) col;
174            }
175            return new HashBag<>(col);
176        }
177        return null;
178    }
179
180    // Factory Methods
181    // -----------------------------------------------------------------------
182
183    /**
184     * Creates a {@link ListValuedMap} with an {@link java.util.ArrayList ArrayList} as
185     * collection class to store the values mapped to a key.
186     *
187     * @param <K> the key type
188     * @param <V> the value type
189     * @return a new <code>ListValuedMap</code>
190     */
191    public static <K, V> ListValuedMap<K, V> newListValuedHashMap() {
192        return new ArrayListValuedHashMap<>();
193    }
194
195    /**
196     * Creates a {@link SetValuedMap} with an {@link java.util.HashSet HashSet} as
197     * collection class to store the values mapped to a key.
198     *
199     * @param <K> the key type
200     * @param <V> the value type
201     * @return a new {@link SetValuedMap}
202     */
203    public static <K, V> SetValuedMap<K, V> newSetValuedHashMap() {
204        return new HashSetValuedHashMap<>();
205    }
206
207    // MultiValuedMap Decorators
208    // -----------------------------------------------------------------------
209
210    /**
211     * Returns an <code>UnmodifiableMultiValuedMap</code> backed by the given
212     * map.
213     *
214     * @param <K> the key type
215     * @param <V> the value type
216     * @param map  the {@link MultiValuedMap} to decorate, must not be null
217     * @return an unmodifiable {@link MultiValuedMap} backed by the provided map
218     * @throws NullPointerException if map is null
219     */
220    public static <K, V> MultiValuedMap<K, V> unmodifiableMultiValuedMap(
221            final MultiValuedMap<? extends K, ? extends V> map) {
222        return UnmodifiableMultiValuedMap.<K, V>unmodifiableMultiValuedMap(map);
223    }
224
225    /**
226     * Returns a <code>TransformedMultiValuedMap</code> backed by the given map.
227     * <p>
228     * This method returns a new <code>MultiValuedMap</code> (decorating the
229     * specified map) that will transform any new entries added to it. Existing
230     * entries in the specified map will not be transformed. If you want that
231     * behaviour, see {@link TransformedMultiValuedMap#transformedMap}.
232     * <p>
233     * Each object is passed through the transformers as it is added to the Map.
234     * It is important not to use the original map after invoking this method,
235     * as it is a back door for adding untransformed objects.
236     * <p>
237     * If there are any elements already in the map being decorated, they are
238     * NOT transformed.
239     *
240     * @param <K> the key type
241     * @param <V> the value type
242     * @param map  the {@link MultiValuedMap} to transform, must not be null, typically empty
243     * @param keyTransformer  the transformer for the map keys, null means no transformation
244     * @param valueTransformer  the transformer for the map values, null means no transformation
245     * @return a transformed <code>MultiValuedMap</code> backed by the given map
246     * @throws NullPointerException if map is null
247     */
248    public static <K, V> MultiValuedMap<K, V> transformedMultiValuedMap(final MultiValuedMap<K, V> map,
249            final Transformer<? super K, ? extends K> keyTransformer,
250            final Transformer<? super V, ? extends V> valueTransformer) {
251        return TransformedMultiValuedMap.transformingMap(map, keyTransformer, valueTransformer);
252    }
253
254}