    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}