https://github.com/eclipse-ee4j/jaxrs-api: Jakarta RESTful Web Services (Eclipse Foundation) 
/*
 * Copyright (c) 2011, 2019 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package jakarta.ws.rs.core;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.ConcurrentModificationException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


A hash table based implementation of MultivaluedMap interface. 
 This implementation provides all of the optional map operations. This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time. The implementation permits null key. By default the implementation does also permit null values, but ignores them. This behavior can be customized by overriding the protected addNull(...) and addFirstNull(...) methods. 


 This implementation provides constant-time performance for the basic operations (get and put), assuming the hash function disperses the elements properly among the buckets. Iteration over collection views requires time proportional to the "capacity" of the map instance (the number of buckets) plus its size (the number of key-value mappings). Thus, it's very important not to set the initial capacity too high (or the load factor too low) if iteration performance is important. 


 An instance of MultivaluedHashMap has two parameters that affect its performance: initial capacity
and load factor. The capacity is the number of buckets in the hash table, and the initial capacity is
simply the capacity at the time the hash table is created. The load factor is a measure of how full the hash
table is allowed to get before its capacity is automatically increased. When the number of entries in the hash table
exceeds the product of the load factor and the current capacity, the hash table is rehashed (that is, internal
data structures are rebuilt) so that the hash table has approximately twice the number of buckets.



 As a general rule, the default load factor (.75) offers a good tradeoff between time and space costs. Higher values decrease the space overhead but increase the lookup cost (reflected in most of the operations of the HashMap class, including get and put). The expected number of entries in the map and its load factor should be taken into account when setting its initial capacity, so as to minimize the number of rehash operations. If the initial capacity is greater than the maximum number of entries divided by the load factor, no rehash operations will ever occur. 


 If many mappings are to be stored in a MultivaluedHashMap instance, creating it with a sufficiently large capacity will allow the mappings to be stored more efficiently than letting it perform automatic rehashing as needed to grow the table. 



Note that this implementation is not guaranteed to be synchronized. If multiple threads access a
hash map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized
externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing
the value associated with a key that an instance already contains is not a structural modification.) This is
typically accomplished by synchronizing on some object that naturally encapsulates the map.




The iterators returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future. 
 Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect
bugs.

Author:Paul Sandoz, Marek Potociar
Type parameters:
  • <K> – the type of keys maintained by this map.
  • <V> – the type of mapped values.
Since:2.0
/**
 * A hash table based implementation of {@link MultivaluedMap} interface.
 *
 * <p>
 * This implementation provides all of the optional map operations. This class makes no guarantees as to the order of
 * the map; in particular, it does not guarantee that the order will remain constant over time. The implementation
 * permits {@code null} key. By default the implementation does also permit {@code null} values, but ignores them. This
 * behavior can be customized by overriding the protected {@link #addNull(List) addNull(...)} and
 * {@link #addFirstNull(List) addFirstNull(...)} methods.
 * </p>
 * <p>
 * This implementation provides constant-time performance for the basic operations ({@code get} and {@code put}),
 * assuming the hash function disperses the elements properly among the buckets. Iteration over collection views
 * requires time proportional to the "capacity" of the map instance (the number of buckets) plus its size (the number of
 * key-value mappings). Thus, it's very important not to set the initial capacity too high (or the load factor too low)
 * if iteration performance is important.
 * </p>
 * <p>
 * An instance of {@code MultivaluedHashMap} has two parameters that affect its performance: <i>initial capacity</i>
 * and <i>load factor</i>. The <i>capacity</i> is the number of buckets in the hash table, and the initial capacity is
 * simply the capacity at the time the hash table is created. The <i>load factor</i> is a measure of how full the hash
 * table is allowed to get before its capacity is automatically increased. When the number of entries in the hash table
 * exceeds the product of the load factor and the current capacity, the hash table is <i>rehashed</i> (that is, internal
 * data structures are rebuilt) so that the hash table has approximately twice the number of buckets.
 * </p>
 * <p>
 * As a general rule, the default load factor (.75) offers a good tradeoff between time and space costs. Higher values
 * decrease the space overhead but increase the lookup cost (reflected in most of the operations of the {@code HashMap}
 * class, including {@code get} and {@code put}). The expected number of entries in the map and its load factor should
 * be taken into account when setting its initial capacity, so as to minimize the number of rehash operations. If the
 * initial capacity is greater than the maximum number of entries divided by the load factor, no rehash operations will
 * ever occur.
 * </p>
 * <p>
 * If many mappings are to be stored in a {@code MultivaluedHashMap} instance, creating it with a sufficiently large
 * capacity will allow the mappings to be stored more efficiently than letting it perform automatic rehashing as needed
 * to grow the table.
 * </p>
 * <p>
 * <strong>Note that this implementation is not guaranteed to be synchronized.</strong> If multiple threads access a
 * hash map concurrently, and at least one of the threads modifies the map structurally, it <i>must</i> be synchronized
 * externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing
 * the value associated with a key that an instance already contains is not a structural modification.) This is
 * typically accomplished by synchronizing on some object that naturally encapsulates the map.
 * </p>
 * <p>
 * The iterators returned by all of this class's "collection view methods" are <i>fail-fast</i>: if the map is
 * structurally modified at any time after the iterator is created, in any way except through the iterator's own
 * {@code remove} method, the iterator will throw a {@link ConcurrentModificationException}. Thus, in the face of
 * concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic
 * behavior at an undetermined time in the future.
 * </p>
 * Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make
 * any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw
 * {@code ConcurrentModificationException} on a best-effort basis. Therefore, it would be wrong to write a program that
 * depended on this exception for its correctness: <i>the fail-fast behavior of iterators should be used only to detect
 * bugs.</i>
 *
 * @param <K> the type of keys maintained by this map.
 * @param <V> the type of mapped values.
 * @author Paul Sandoz
 * @author Marek Potociar
 * @since 2.0
 */
public class MultivaluedHashMap<K, V> extends AbstractMultivaluedMap<K, V> implements Serializable {

    private static final long serialVersionUID = -6052320403766368902L;

    
Constructs an empty multivalued hash map with the default initial capacity (16) and the default load factor (0.75). 
/**
     * Constructs an empty multivalued hash map with the default initial capacity ({@code 16}) and the default load factor
     * ({@code 0.75}).
     */
    public MultivaluedHashMap() {
        super(new HashMap<K, List<V>>());
    }

    
Constructs an empty multivalued hash map with the specified initial capacity and the default load factor (0.75). 
Params:
  • initialCapacity – the initial capacity.
Throws:
/**
     * Constructs an empty multivalued hash map with the specified initial capacity and the default load factor
     * ({@code 0.75}).
     *
     * @param initialCapacity the initial capacity.
     * @throws IllegalArgumentException if the initial capacity is negative.
     */
    public MultivaluedHashMap(final int initialCapacity) {
        super(new HashMap<K, List<V>>(initialCapacity));
    }

    
Constructs an empty multivalued hash map with the specified initial capacity and load factor.

Params:
  • initialCapacity – the initial capacity
  • loadFactor – the load factor
Throws:
/**
     * Constructs an empty multivalued hash map with the specified initial capacity and load factor.
     *
     * @param initialCapacity the initial capacity
     * @param loadFactor the load factor
     * @throws IllegalArgumentException if the initial capacity is negative or the load factor is nonpositive
     */
    public MultivaluedHashMap(final int initialCapacity, final float loadFactor) {
        super(new HashMap<K, List<V>>(initialCapacity, loadFactor));
    }

    
Constructs a new multivalued hash map with the same mappings as the specified MultivaluedMap. The List instances holding the values of each key are created anew instead of being reused. 
Params:
  • map – the multivalued map whose mappings are to be placed in this multivalued map.
Throws:
/**
     * Constructs a new multivalued hash map with the same mappings as the specified {@link MultivaluedMap }. The
     * {@link List} instances holding the values of each key are created anew instead of being reused.
     *
     * @param map the multivalued map whose mappings are to be placed in this multivalued map.
     * @throws NullPointerException if the specified map is {@code null}
     */
    public MultivaluedHashMap(final MultivaluedMap<? extends K, ? extends V> map) {
        this();
        putAll(map);
    }

    
This private method is used by the copy constructor to avoid exposing additional generic parameters through the
public API documentation.

Params:
  • map – the map
Type parameters:
  • <T> – any subclass of K
  • <U> – any subclass of V
/**
     * This private method is used by the copy constructor to avoid exposing additional generic parameters through the
     * public API documentation.
     *
     * @param <T> any subclass of K
     * @param <U> any subclass of V
     * @param map the map
     */
    private <T extends K, U extends V> void putAll(final MultivaluedMap<T, U> map) {
        for (Entry<T, List<U>> e : map.entrySet()) {
            store.put(e.getKey(), new ArrayList<V>(e.getValue()));
        }
    }

    
Constructs a new multivalued hash map with the same mappings as the specified single-valued Map. 
Params:
  • map – the single-valued map whose mappings are to be placed in this multivalued map.
Throws:
/**
     * Constructs a new multivalued hash map with the same mappings as the specified single-valued {@link Map }.
     *
     * @param map the single-valued map whose mappings are to be placed in this multivalued map.
     * @throws NullPointerException if the specified map is {@code null}
     */
    public MultivaluedHashMap(final Map<? extends K, ? extends V> map) {
        this();
        for (Entry<? extends K, ? extends V> e : map.entrySet()) {
            this.putSingle(e.getKey(), e.getValue());
        }
    }
}