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| 1 | +/* | |
| 2 | + * Copyright (c) 2008, Oracle and/or its affiliates. All rights reserved. | |
| 3 | + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| 4 | + * | |
| 5 | + * This code is free software; you can redistribute it and/or modify it | |
| 6 | + * under the terms of the GNU General Public License version 2 only, as | |
| 7 | + * published by the Free Software Foundation. Oracle designates this | |
| 8 | + * particular file as subject to the "Classpath" exception as provided | |
| 9 | + * by Oracle in the LICENSE file that accompanied this code. | |
| 10 | + * | |
| 11 | + * This code is distributed in the hope that it will be useful, but WITHOUT | |
| 12 | + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 13 | + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 14 | + * version 2 for more details (a copy is included in the LICENSE file that | |
| 15 | + * accompanied this code). | |
| 16 | + * | |
| 17 | + * You should have received a copy of the GNU General Public License version | |
| 18 | + * 2 along with this work; if not, write to the Free Software Foundation, | |
| 19 | + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| 20 | + * | |
| 21 | + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 22 | + * or visit www.oracle.com if you need additional information or have any | |
| 23 | + * questions. | |
| 24 | + */ | |
| 25 | +package com.sun.beans; | |
| 26 | + | |
| 27 | +import java.lang.ref.Reference; | |
| 28 | +import java.lang.ref.WeakReference; | |
| 29 | + | |
| 30 | +import java.util.Map; | |
| 31 | +import java.util.WeakHashMap; | |
| 32 | + | |
| 33 | +/** | |
| 34 | + * A hashtable-based cache with weak keys and weak values. | |
| 35 | + * An entry in the map will be automatically removed | |
| 36 | + * when its key is no longer in the ordinary use. | |
| 37 | + * A value will be automatically removed as well | |
| 38 | + * when it is no longer in the ordinary use. | |
| 39 | + * | |
| 40 | + * @since 1.7 | |
| 41 | + * | |
| 42 | + * @author Sergey A. Malenkov | |
| 43 | + */ | |
| 44 | +public final class WeakCache<K, V> { | |
| 45 | + private final Map<K, Reference<V>> map = new WeakHashMap<K, Reference<V>>(); | |
| 46 | + | |
| 47 | + /** | |
| 48 | + * Returns a value to which the specified {@code key} is mapped, | |
| 49 | + * or {@code null} if this map contains no mapping for the {@code key}. | |
| 50 | + * | |
| 51 | + * @param key the key whose associated value is returned | |
| 52 | + * @return a value to which the specified {@code key} is mapped | |
| 53 | + */ | |
| 54 | + public V get(K key) { | |
| 55 | + Reference<V> reference = this.map.get(key); | |
| 56 | + if (reference == null) { | |
| 57 | + return null; | |
| 58 | + } | |
| 59 | + V value = reference.get(); | |
| 60 | + if (value == null) { | |
| 61 | + this.map.remove(key); | |
| 62 | + } | |
| 63 | + return value; | |
| 64 | + } | |
| 65 | + | |
| 66 | + /** | |
| 67 | + * Associates the specified {@code value} with the specified {@code key}. | |
| 68 | + * Removes the mapping for the specified {@code key} from this cache | |
| 69 | + * if it is present and the specified {@code value} is {@code null}. | |
| 70 | + * If the cache previously contained a mapping for the {@code key}, | |
| 71 | + * the old value is replaced by the specified {@code value}. | |
| 72 | + * | |
| 73 | + * @param key the key with which the specified value is associated | |
| 74 | + * @param value the value to be associated with the specified key | |
| 75 | + */ | |
| 76 | + public void put(K key, V value) { | |
| 77 | + if (value != null) { | |
| 78 | + this.map.put(key, new WeakReference<V>(value)); | |
| 79 | + } | |
| 80 | + else { | |
| 81 | + this.map.remove(key); | |
| 82 | + } | |
| 83 | + } | |
| 84 | + | |
| 85 | + /** | |
| 86 | + * Removes all of the mappings from this cache. | |
| 87 | + */ | |
| 88 | + public void clear() { | |
| 89 | + this.map.clear(); | |
| 90 | + } | |
| 91 | +} | |