MultiMapUtils.java
/*
* 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.
* <p>
* It contains various type safe and null safe methods. Additionally, it provides
* the following decorators:
* </p>
* <ul>
* <li>{@link #unmodifiableMultiValuedMap(MultiValuedMap)}</li>
* <li>{@link #transformedMultiValuedMap(MultiValuedMap, Transformer, Transformer)}</li>
* </ul>
*
* @since 4.1
*/
public class MultiMapUtils {
/**
* An empty {@link UnmodifiableMultiValuedMap}.
*/
@SuppressWarnings({ "rawtypes", "unchecked" })
public static final MultiValuedMap EMPTY_MULTI_VALUED_MAP =
UnmodifiableMultiValuedMap.unmodifiableMultiValuedMap(new ArrayListValuedHashMap(0, 0));
/**
* Returns an immutable empty {@code MultiValuedMap} if the argument is
* {@code null}, or the argument itself otherwise.
*
* @param <K> the type of key in the map
* @param <V> 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 <K, V> MultiValuedMap<K, V> emptyIfNull(final MultiValuedMap<K, V> map) {
return map == null ? EMPTY_MULTI_VALUED_MAP : map;
}
/**
* Returns immutable EMPTY_MULTI_VALUED_MAP with generic type safety.
*
* @param <K> the type of key in the map
* @param <V> the type of value in the map
* @return immutable and empty {@code MultiValuedMap}
*/
@SuppressWarnings("unchecked")
public static <K, V> MultiValuedMap<K, V> emptyMultiValuedMap() {
return EMPTY_MULTI_VALUED_MAP;
}
// Null safe methods
/**
* Gets a Collection from {@code MultiValuedMap} in a null-safe manner.
*
* @param <K> the key type
* @param <V> 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 <K, V> Collection<V> getCollection(final MultiValuedMap<K, V> map, final K key) {
if (map != null) {
return map.get(key);
}
return null;
}
/**
* Gets a Bag from {@code MultiValuedMap} in a null-safe manner.
*
* @param <K> the key type
* @param <V> 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 <K, V> Bag<V> getValuesAsBag(final MultiValuedMap<K, V> map, final K key) {
if (map != null) {
final Collection<V> col = map.get(key);
if (col instanceof Bag) {
return (Bag<V>) col;
}
return new HashBag<>(col);
}
return null;
}
/**
* Gets a List from {@code MultiValuedMap} in a null-safe manner.
*
* @param <K> the key type
* @param <V> 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 <K, V> List<V> getValuesAsList(final MultiValuedMap<K, V> map, final K key) {
if (map != null) {
final Collection<V> col = map.get(key);
if (col instanceof List) {
return (List<V>) col;
}
return new ArrayList<>(col);
}
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 Set from {@code MultiValuedMap} in a null-safe manner.
*
* @param <K> the key type
* @param <V> 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 <K, V> Set<V> getValuesAsSet(final MultiValuedMap<K, V> map, final K key) {
if (map != null) {
final Collection<V> col = map.get(key);
if (col instanceof Set) {
return (Set<V>) col;
}
return new HashSet<>(col);
}
return null;
}
/**
* Null-safe check if the specified {@code MultiValuedMap} is empty.
* <p>
* 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();
}
/**
* Creates a {@link ListValuedMap} with an {@link java.util.ArrayList ArrayList} as
* collection class to store the values mapped to a key.
*
* @param <K> the key type
* @param <V> the value type
* @return a new {@code ListValuedMap}
*/
public static <K, V> ListValuedMap<K, V> 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 <K> the key type
* @param <V> the value type
* @return a new {@link SetValuedMap}
*/
public static <K, V> SetValuedMap<K, V> newSetValuedHashMap() {
return new HashSetValuedHashMap<>();
}
/**
* Returns a {@code TransformedMultiValuedMap} backed by the given map.
* <p>
* This method returns a new {@code 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
* behavior, see {@link TransformedMultiValuedMap#transformedMap}.
* <p>
* 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.
* <p>
* If there are any elements already in the map being decorated, they are
* NOT transformed.
*
* @param <K> the key type
* @param <V> 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 {@code MultiValuedMap} backed by the given map
* @throws NullPointerException if map is null
*/
public static <K, V> MultiValuedMap<K, V> transformedMultiValuedMap(final MultiValuedMap<K, V> map,
final Transformer<? super K, ? extends K> keyTransformer,
final Transformer<? super V, ? extends V> valueTransformer) {
return TransformedMultiValuedMap.transformingMap(map, keyTransformer, valueTransformer);
}
/**
* Returns an {@code UnmodifiableMultiValuedMap} backed by the given
* map.
*
* @param <K> the key type
* @param <V> 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 <K, V> MultiValuedMap<K, V> unmodifiableMultiValuedMap(
final MultiValuedMap<? extends K, ? extends V> map) {
return UnmodifiableMultiValuedMap.<K, V>unmodifiableMultiValuedMap(map);
}
/**
* Don't allow instances.
*/
private MultiMapUtils() {}
}