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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.collections4;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.apache.commons.collections4.bag.HashBag;
import org.apache.commons.collections4.multimap.ArrayListValuedHashMap;
import org.apache.commons.collections4.multimap.HashSetValuedHashMap;
import org.apache.commons.collections4.multimap.TransformedMultiValuedMap;
import org.apache.commons.collections4.multimap.UnmodifiableMultiValuedMap;

/**
 * Provides utility methods and decorators for {@link MultiValuedMap} instances.
 * 

* It contains various type safe and null safe methods. Additionally, it provides * the following decorators: *

    *
  • {@link #unmodifiableMultiValuedMap(MultiValuedMap)}
  • *
  • {@link #transformedMultiValuedMap(MultiValuedMap, Transformer, Transformer)}
  • *
* * @since 4.1 * @version $Id: MultiMapUtils.java 1715302 2015-11-19 23:08:01Z tn $ */ public class MultiMapUtils { /** * MultiMapUtils should not normally be instantiated. */ private MultiMapUtils() {} /** * An empty {@link UnmodifiableMultiValuedMap}. */ @SuppressWarnings({ "rawtypes", "unchecked" }) public static final MultiValuedMap EMPTY_MULTI_VALUED_MAP = UnmodifiableMultiValuedMap.unmodifiableMultiValuedMap(new ArrayListValuedHashMap(0, 0)); /** * Returns immutable EMPTY_MULTI_VALUED_MAP with generic type safety. * * @param the type of key in the map * @param the type of value in the map * @return immutable and empty MultiValuedMap */ @SuppressWarnings("unchecked") public static MultiValuedMap emptyMultiValuedMap() { return EMPTY_MULTI_VALUED_MAP; } // Null safe methods /** * Returns an immutable empty MultiValuedMap if the argument is * null, or the argument itself otherwise. * * @param the type of key in the map * @param the type of value in the map * @param map the map, may be null * @return an empty {@link MultiValuedMap} if the argument is null */ @SuppressWarnings("unchecked") public static MultiValuedMap emptyIfNull(final MultiValuedMap map) { return map == null ? EMPTY_MULTI_VALUED_MAP : map; } /** * Null-safe check if the specified MultiValuedMap is empty. *

* If the provided map is null, returns true. * * @param map the map to check, may be null * @return true if the map is empty or null */ public static boolean isEmpty(final MultiValuedMap map) { return map == null || map.isEmpty(); } // Null safe getters // ------------------------------------------------------------------------- /** * Gets a Collection from MultiValuedMap in a null-safe manner. * * @param the key type * @param the value type * @param map the {@link MultiValuedMap} to use * @param key the key to look up * @return the Collection in the {@link MultiValuedMap}, or null if input map is null */ public static Collection getCollection(final MultiValuedMap map, final K key) { if (map != null) { return map.get(key); } return null; } // TODO: review the getValuesAsXXX methods - depending on the actual MultiValuedMap type, changes // to the returned collection might update the backing map. This should be clarified and/or prevented. /** * Gets a List from MultiValuedMap in a null-safe manner. * * @param the key type * @param the value type * @param map the {@link MultiValuedMap} to use * @param key the key to look up * @return the Collection in the {@link MultiValuedMap} as List, or null if input map is null */ public static List getValuesAsList(final MultiValuedMap map, final K key) { if (map != null) { Collection col = map.get(key); if (col instanceof List) { return (List) col; } return new ArrayList(col); } return null; } /** * Gets a Set from MultiValuedMap in a null-safe manner. * * @param the key type * @param the value type * @param map the {@link MultiValuedMap} to use * @param key the key to look up * @return the Collection in the {@link MultiValuedMap} as Set, or null if input map is null */ public static Set getValuesAsSet(final MultiValuedMap map, final K key) { if (map != null) { Collection col = map.get(key); if (col instanceof Set) { return (Set) col; } return new HashSet(col); } return null; } /** * Gets a Bag from MultiValuedMap in a null-safe manner. * * @param the key type * @param the value type * @param map the {@link MultiValuedMap} to use * @param key the key to look up * @return the Collection in the {@link MultiValuedMap} as Bag, or null if input map is null */ public static Bag getValuesAsBag(final MultiValuedMap map, final K key) { if (map != null) { Collection col = map.get(key); if (col instanceof Bag) { return (Bag) col; } return new HashBag(col); } return null; } // Factory Methods // ----------------------------------------------------------------------- /** * Creates a {@link ListValuedMap} with an {@link java.util.ArrayList ArrayList} as * collection class to store the values mapped to a key. * * @param the key type * @param the value type * @return a new ListValuedMap */ public static ListValuedMap newListValuedHashMap() { return new ArrayListValuedHashMap(); } /** * Creates a {@link SetValuedMap} with an {@link java.util.HashSet HashSet} as * collection class to store the values mapped to a key. * * @param the key type * @param the value type * @return a new {@link SetValuedMap} */ public static SetValuedMap newSetValuedHashMap() { return new HashSetValuedHashMap(); } // MultiValuedMap Decorators // ----------------------------------------------------------------------- /** * Returns an UnmodifiableMultiValuedMap backed by the given * map. * * @param the key type * @param the value type * @param map the {@link MultiValuedMap} to decorate, must not be null * @return an unmodifiable {@link MultiValuedMap} backed by the provided map * @throws NullPointerException if map is null */ public static MultiValuedMap unmodifiableMultiValuedMap( final MultiValuedMap map) { return UnmodifiableMultiValuedMap.unmodifiableMultiValuedMap(map); } /** * Returns a TransformedMultiValuedMap backed by the given map. *

* This method returns a new MultiValuedMap (decorating the * specified map) that will transform any new entries added to it. Existing * entries in the specified map will not be transformed. If you want that * behaviour, see {@link TransformedMultiValuedMap#transformedMap}. *

* 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 is a back door for adding untransformed objects. *

* If there are any elements already in the map being decorated, they are * NOT transformed. * * @param the key type * @param the value type * @param map the {@link MultiValuedMap} to transform, must not be null, typically empty * @param keyTransformer the transformer for the map keys, null means no transformation * @param valueTransformer the transformer for the map values, null means no transformation * @return a transformed MultiValuedMap backed by the given map * @throws NullPointerException if map is null */ public static MultiValuedMap transformedMultiValuedMap(final MultiValuedMap map, final Transformer keyTransformer, final Transformer valueTransformer) { return TransformedMultiValuedMap.transformingMap(map, keyTransformer, valueTransformer); } }





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