Java tutorial
/* * Copyright 2002-2019 the original author or authors. * * Licensed 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 * * https://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.springframework.util; import java.io.Serializable; import java.util.Collection; import java.util.LinkedHashMap; import java.util.LinkedList; import java.util.List; import java.util.Map; import java.util.Set; import org.springframework.lang.Nullable; /** * Simple implementation of {@link MultiValueMap} that wraps a {@link LinkedHashMap}, * storing multiple values in a {@link LinkedList}. * * <p>This Map implementation is generally not thread-safe. It is primarily designed * for data structures exposed from request objects, for use in a single thread only. * * @author Arjen Poutsma * @author Juergen Hoeller * @since 3.0 * @param <K> the key type * @param <V> the value element type */ public class LinkedMultiValueMap<K, V> implements MultiValueMap<K, V>, Serializable, Cloneable { private static final long serialVersionUID = 3801124242820219131L; private final Map<K, List<V>> targetMap; /** * Create a new LinkedMultiValueMap that wraps a {@link LinkedHashMap}. */ public LinkedMultiValueMap() { this.targetMap = new LinkedHashMap<>(); } /** * Create a new LinkedMultiValueMap that wraps a {@link LinkedHashMap} * with the given initial capacity. * @param initialCapacity the initial capacity */ public LinkedMultiValueMap(int initialCapacity) { this.targetMap = new LinkedHashMap<>(initialCapacity); } /** * Copy constructor: Create a new LinkedMultiValueMap with the same mappings as * the specified Map. Note that this will be a shallow copy; its value-holding * List entries will get reused and therefore cannot get modified independently. * @param otherMap the Map whose mappings are to be placed in this Map * @see #clone() * @see #deepCopy() */ public LinkedMultiValueMap(Map<K, List<V>> otherMap) { this.targetMap = new LinkedHashMap<>(otherMap); } // MultiValueMap implementation @Override @Nullable public V getFirst(K key) { List<V> values = this.targetMap.get(key); return (values != null && !values.isEmpty() ? values.get(0) : null); } @Override public void add(K key, @Nullable V value) { List<V> values = this.targetMap.computeIfAbsent(key, k -> new LinkedList<>()); values.add(value); } @Override public void addAll(K key, List<? extends V> values) { List<V> currentValues = this.targetMap.computeIfAbsent(key, k -> new LinkedList<>()); currentValues.addAll(values); } @Override public void addAll(MultiValueMap<K, V> values) { for (Entry<K, List<V>> entry : values.entrySet()) { addAll(entry.getKey(), entry.getValue()); } } @Override public void set(K key, @Nullable V value) { List<V> values = new LinkedList<>(); values.add(value); this.targetMap.put(key, values); } @Override public void setAll(Map<K, V> values) { values.forEach(this::set); } @Override public Map<K, V> toSingleValueMap() { LinkedHashMap<K, V> singleValueMap = new LinkedHashMap<>(this.targetMap.size()); this.targetMap.forEach((key, values) -> { if (values != null && !values.isEmpty()) { singleValueMap.put(key, values.get(0)); } }); return singleValueMap; } // Map implementation @Override public int size() { return this.targetMap.size(); } @Override public boolean isEmpty() { return this.targetMap.isEmpty(); } @Override public boolean containsKey(Object key) { return this.targetMap.containsKey(key); } @Override public boolean containsValue(Object value) { return this.targetMap.containsValue(value); } @Override @Nullable public List<V> get(Object key) { return this.targetMap.get(key); } @Override @Nullable public List<V> put(K key, List<V> value) { return this.targetMap.put(key, value); } @Override @Nullable public List<V> remove(Object key) { return this.targetMap.remove(key); } @Override public void putAll(Map<? extends K, ? extends List<V>> map) { this.targetMap.putAll(map); } @Override public void clear() { this.targetMap.clear(); } @Override public Set<K> keySet() { return this.targetMap.keySet(); } @Override public Collection<List<V>> values() { return this.targetMap.values(); } @Override public Set<Entry<K, List<V>>> entrySet() { return this.targetMap.entrySet(); } /** * Create a deep copy of this Map. * @return a copy of this Map, including a copy of each value-holding List entry * (consistently using an independent modifiable {@link LinkedList} for each entry) * along the lines of {@code MultiValueMap.addAll} semantics * @since 4.2 * @see #addAll(MultiValueMap) * @see #clone() */ public LinkedMultiValueMap<K, V> deepCopy() { LinkedMultiValueMap<K, V> copy = new LinkedMultiValueMap<>(this.targetMap.size()); this.targetMap.forEach((key, value) -> copy.put(key, new LinkedList<>(value))); return copy; } /** * Create a regular copy of this Map. * @return a shallow copy of this Map, reusing this Map's value-holding List entries * (even if some entries are shared or unmodifiable) along the lines of standard * {@code Map.put} semantics * @since 4.2 * @see #put(Object, List) * @see #putAll(Map) * @see LinkedMultiValueMap#LinkedMultiValueMap(Map) * @see #deepCopy() */ @Override public LinkedMultiValueMap<K, V> clone() { return new LinkedMultiValueMap<>(this); } @Override public boolean equals(@Nullable Object obj) { return this.targetMap.equals(obj); } @Override public int hashCode() { return this.targetMap.hashCode(); } @Override public String toString() { return this.targetMap.toString(); } }