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javax.ws.rs.core.MultivaluedHashMap Maven / Gradle / Ivy

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 2011-2012 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * http://glassfish.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
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 * elects to include this software in this distribution under the [CDDL or GPL
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package javax.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 {@link 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 {@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.
 * 

 * 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 {@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.
 * 

 * 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.
 *
 * @param  the type of keys maintained by this map.
 * @param  the type of mapped values.
 * @author Paul Sandoz
 * @author Marek Potociar
 * @since 2.0
 */
public class MultivaluedHashMap extends AbstractMultivaluedMap implements Serializable {

    private static final long serialVersionUID = -6052320403766368902L;

    /**
     * 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>());
    }

    /**
     * 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(int initialCapacity) {
        super(new HashMap>(initialCapacity));
    }

    /**
     * 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(int initialCapacity, float loadFactor) {
        super(new HashMap>(initialCapacity, loadFactor));
    }

    /**
     * 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(MultivaluedMap map) {
        this();
        putAll(map);
    }

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

    /**
     * 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(Map map) {
        this();
        for (Entry e : map.entrySet()) {
            this.putSingle(e.getKey(), e.getValue());
        }
    }
}