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 * <ul>
037 *   <li>{@link #unmodifiableMultiValuedMap(MultiValuedMap)}</li>
038 *   <li>{@link #transformedMultiValuedMap(MultiValuedMap, Transformer, Transformer)}</li>
039 * </ul>
040 *
041 * @since 4.1
042 */
043public class MultiMapUtils {
044
045    /**
046     * <code>MultiMapUtils</code> should not normally be instantiated.
047     */
048    private MultiMapUtils() {}
049
050    /**
051     * An empty {@link UnmodifiableMultiValuedMap}.
052     */
053    @SuppressWarnings({ "rawtypes", "unchecked" })
054    public static final MultiValuedMap EMPTY_MULTI_VALUED_MAP =
055            UnmodifiableMultiValuedMap.unmodifiableMultiValuedMap(new ArrayListValuedHashMap(0, 0));
056
057    /**
058     * Returns immutable EMPTY_MULTI_VALUED_MAP with generic type safety.
059     *
060     * @param <K> the type of key in the map
061     * @param <V> the type of value in the map
062     * @return immutable and empty <code>MultiValuedMap</code>
063     */
064    @SuppressWarnings("unchecked")
065    public static <K, V> MultiValuedMap<K, V> emptyMultiValuedMap() {
066        return EMPTY_MULTI_VALUED_MAP;
067    }
068
069    // Null safe methods
070
071    /**
072     * Returns an immutable empty <code>MultiValuedMap</code> if the argument is
073     * <code>null</code>, or the argument itself otherwise.
074     *
075     * @param <K> the type of key in the map
076     * @param <V> the type of value in the map
077     * @param map  the map, may be null
078     * @return an empty {@link MultiValuedMap} if the argument is null
079     */
080    @SuppressWarnings("unchecked")
081    public static <K, V> MultiValuedMap<K, V> emptyIfNull(final MultiValuedMap<K, V> map) {
082        return map == null ? EMPTY_MULTI_VALUED_MAP : map;
083    }
084
085    /**
086     * Null-safe check if the specified <code>MultiValuedMap</code> is empty.
087     * <p>
088     * If the provided map is null, returns true.
089     *
090     * @param map  the map to check, may be null
091     * @return true if the map is empty or null
092     */
093    public static boolean isEmpty(final MultiValuedMap<?, ?> map) {
094        return map == null || map.isEmpty();
095    }
096
097    // Null safe getters
098    // -------------------------------------------------------------------------
099
100    /**
101     * Gets a Collection from <code>MultiValuedMap</code> in a null-safe manner.
102     *
103     * @param <K> the key type
104     * @param <V> the value type
105     * @param map  the {@link MultiValuedMap} to use
106     * @param key  the key to look up
107     * @return the Collection in the {@link MultiValuedMap}, or null if input map is null
108     */
109    public static <K, V> Collection<V> getCollection(final MultiValuedMap<K, V> map, final K key) {
110        if (map != null) {
111            return map.get(key);
112        }
113        return null;
114    }
115
116    // TODO: review the getValuesAsXXX methods - depending on the actual MultiValuedMap type, changes
117    // to the returned collection might update the backing map. This should be clarified and/or prevented.
118
119    /**
120     * Gets a List from <code>MultiValuedMap</code> in a null-safe manner.
121     *
122     * @param <K> the key type
123     * @param <V> the value type
124     * @param map  the {@link MultiValuedMap} to use
125     * @param key  the key to look up
126     * @return the Collection in the {@link MultiValuedMap} as List, or null if input map is null
127     */
128    public static <K, V> List<V> getValuesAsList(final MultiValuedMap<K, V> map, final K key) {
129        if (map != null) {
130            final Collection<V> col = map.get(key);
131            if (col instanceof List) {
132                return (List<V>) col;
133            }
134            return new ArrayList<>(col);
135        }
136        return null;
137    }
138
139    /**
140     * Gets a Set from <code>MultiValuedMap</code> in a null-safe manner.
141     *
142     * @param <K> the key type
143     * @param <V> the value type
144     * @param map  the {@link MultiValuedMap} to use
145     * @param key  the key to look up
146     * @return the Collection in the {@link MultiValuedMap} as Set, or null if input map is null
147     */
148    public static <K, V> Set<V> getValuesAsSet(final MultiValuedMap<K, V> map, final K key) {
149        if (map != null) {
150            final Collection<V> col = map.get(key);
151            if (col instanceof Set) {
152                return (Set<V>) col;
153            }
154            return new HashSet<>(col);
155        }
156        return null;
157    }
158
159    /**
160     * Gets a Bag from <code>MultiValuedMap</code> in a null-safe manner.
161     *
162     * @param <K> the key type
163     * @param <V> the value type
164     * @param map  the {@link MultiValuedMap} to use
165     * @param key  the key to look up
166     * @return the Collection in the {@link MultiValuedMap} as Bag, or null if input map is null
167     */
168    public static <K, V> Bag<V> getValuesAsBag(final MultiValuedMap<K, V> map, final K key) {
169        if (map != null) {
170            final Collection<V> col = map.get(key);
171            if (col instanceof Bag) {
172                return (Bag<V>) col;
173            }
174            return new HashBag<>(col);
175        }
176        return null;
177    }
178
179    // Factory Methods
180    // -----------------------------------------------------------------------
181
182    /**
183     * Creates a {@link ListValuedMap} with an {@link java.util.ArrayList ArrayList} as
184     * collection class to store the values mapped to a key.
185     *
186     * @param <K> the key type
187     * @param <V> the value type
188     * @return a new <code>ListValuedMap</code>
189     */
190    public static <K, V> ListValuedMap<K, V> newListValuedHashMap() {
191        return new ArrayListValuedHashMap<>();
192    }
193
194    /**
195     * Creates a {@link SetValuedMap} with an {@link java.util.HashSet HashSet} as
196     * collection class to store the values mapped to a key.
197     *
198     * @param <K> the key type
199     * @param <V> the value type
200     * @return a new {@link SetValuedMap}
201     */
202    public static <K, V> SetValuedMap<K, V> newSetValuedHashMap() {
203        return new HashSetValuedHashMap<>();
204    }
205
206    // MultiValuedMap Decorators
207    // -----------------------------------------------------------------------
208
209    /**
210     * Returns an <code>UnmodifiableMultiValuedMap</code> backed by the given
211     * map.
212     *
213     * @param <K> the key type
214     * @param <V> the value type
215     * @param map  the {@link MultiValuedMap} to decorate, must not be null
216     * @return an unmodifiable {@link MultiValuedMap} backed by the provided map
217     * @throws NullPointerException if map is null
218     */
219    public static <K, V> MultiValuedMap<K, V> unmodifiableMultiValuedMap(
220            final MultiValuedMap<? extends K, ? extends V> map) {
221        return UnmodifiableMultiValuedMap.<K, V>unmodifiableMultiValuedMap(map);
222    }
223
224    /**
225     * Returns a <code>TransformedMultiValuedMap</code> backed by the given map.
226     * <p>
227     * This method returns a new <code>MultiValuedMap</code> (decorating the
228     * specified map) that will transform any new entries added to it. Existing
229     * entries in the specified map will not be transformed. If you want that
230     * behaviour, see {@link TransformedMultiValuedMap#transformedMap}.
231     * <p>
232     * Each object is passed through the transformers as it is added to the Map.
233     * It is important not to use the original map after invoking this method,
234     * as it is a back door for adding untransformed objects.
235     * <p>
236     * If there are any elements already in the map being decorated, they are
237     * NOT transformed.
238     *
239     * @param <K> the key type
240     * @param <V> the value type
241     * @param map  the {@link MultiValuedMap} to transform, must not be null, typically empty
242     * @param keyTransformer  the transformer for the map keys, null means no transformation
243     * @param valueTransformer  the transformer for the map values, null means no transformation
244     * @return a transformed <code>MultiValuedMap</code> backed by the given map
245     * @throws NullPointerException if map is null
246     */
247    public static <K, V> MultiValuedMap<K, V> transformedMultiValuedMap(final MultiValuedMap<K, V> map,
248            final Transformer<? super K, ? extends K> keyTransformer,
249            final Transformer<? super V, ? extends V> valueTransformer) {
250        return TransformedMultiValuedMap.transformingMap(map, keyTransformer, valueTransformer);
251    }
252
253}