    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     * </p>
    165     *
    166     * @param map  the map to check, may be null
    167     * @return true if the map is empty or null
    168     */
    169    public static boolean isEmpty(final MultiValuedMap<?, ?> map) {
    170        return map == null || map.isEmpty();
    171    }
    172
    173    /**
    174     * Creates a {@link ListValuedMap} with an {@link java.util.ArrayList ArrayList} as
    175     * collection class to store the values mapped to a key.
    176     *
    177     * @param <K> the key type
    178     * @param <V> the value type
    179     * @return a new {@code ListValuedMap}
    180     */
    181    public static <K, V> ListValuedMap<K, V> newListValuedHashMap() {
    182        return new ArrayListValuedHashMap<>();
    183    }
    184
    185    /**
    186     * Creates a {@link SetValuedMap} with an {@link java.util.HashSet HashSet} as
    187     * collection class to store the values mapped to a key.
    188     *
    189     * @param <K> the key type
    190     * @param <V> the value type
    191     * @return a new {@link SetValuedMap}
    192     */
    193    public static <K, V> SetValuedMap<K, V> newSetValuedHashMap() {
    194        return new HashSetValuedHashMap<>();
    195    }
    196
    197    /**
    198     * Returns a {@code TransformedMultiValuedMap} backed by the given map.
    199     * <p>
    200     * This method returns a new {@code MultiValuedMap} (decorating the
    201     * specified map) that will transform any new entries added to it. Existing
    202     * entries in the specified map will not be transformed. If you want that
    203     * behavior, see {@link TransformedMultiValuedMap#transformedMap}.
    204     * </p>
    205     * <p>
    206     * Each object is passed through the transformers as it is added to the Map.
    207     * It is important not to use the original map after invoking this method,
    208     * as it is a back door for adding untransformed objects.
    209     * </p>
    210     * <p>
    211     * If there are any elements already in the map being decorated, they are
    212     * NOT transformed.
    213     * </p>
    214     *
    215     * @param <K> the key type
    216     * @param <V> the value type
    217     * @param map  the {@link MultiValuedMap} to transform, must not be null, typically empty
    218     * @param keyTransformer  the transformer for the map keys, null means no transformation
    219     * @param valueTransformer  the transformer for the map values, null means no transformation
    220     * @return a transformed {@code MultiValuedMap} backed by the given map
    221     * @throws NullPointerException if map is null
    222     */
    223    public static <K, V> MultiValuedMap<K, V> transformedMultiValuedMap(final MultiValuedMap<K, V> map,
    224            final Transformer<? super K, ? extends K> keyTransformer,
    225            final Transformer<? super V, ? extends V> valueTransformer) {
    226        return TransformedMultiValuedMap.transformingMap(map, keyTransformer, valueTransformer);
    227    }
    228
    229    /**
    230     * Returns an {@code UnmodifiableMultiValuedMap} backed by the given
    231     * 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(
    240            final MultiValuedMap<? extends K, ? extends V> map) {
    241        return UnmodifiableMultiValuedMap.<K, V>unmodifiableMultiValuedMap(map);
    242    }
    243
    244    /**
    245     * Don't allow instances.
    246     */
    247    private MultiMapUtils() {
    248        // empty
    249    }
    250
    251}