| /* |
| * Copyright (c) 2008, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| package com.sun.beans; |
| |
| import java.lang.ref.Reference; |
| import java.lang.ref.WeakReference; |
| |
| import java.util.Map; |
| import java.util.WeakHashMap; |
| |
| /** |
| * A hashtable-based cache with weak keys and weak values. |
| * An entry in the map will be automatically removed |
| * when its key is no longer in the ordinary use. |
| * A value will be automatically removed as well |
| * when it is no longer in the ordinary use. |
| * |
| * @since 1.7 |
| * |
| * @author Sergey A. Malenkov |
| */ |
| public final class WeakCache<K, V> { |
| private final Map<K, Reference<V>> map = new WeakHashMap<K, Reference<V>>(); |
| |
| /** |
| * Returns a value to which the specified {@code key} is mapped, |
| * or {@code null} if this map contains no mapping for the {@code key}. |
| * |
| * @param key the key whose associated value is returned |
| * @return a value to which the specified {@code key} is mapped |
| */ |
| public V get(K key) { |
| Reference<V> reference = this.map.get(key); |
| if (reference == null) { |
| return null; |
| } |
| V value = reference.get(); |
| if (value == null) { |
| this.map.remove(key); |
| } |
| return value; |
| } |
| |
| /** |
| * Associates the specified {@code value} with the specified {@code key}. |
| * Removes the mapping for the specified {@code key} from this cache |
| * if it is present and the specified {@code value} is {@code null}. |
| * If the cache previously contained a mapping for the {@code key}, |
| * the old value is replaced by the specified {@code value}. |
| * |
| * @param key the key with which the specified value is associated |
| * @param value the value to be associated with the specified key |
| */ |
| public void put(K key, V value) { |
| if (value != null) { |
| this.map.put(key, new WeakReference<V>(value)); |
| } |
| else { |
| this.map.remove(key); |
| } |
| } |
| |
| /** |
| * Removes all of the mappings from this cache. |
| */ |
| public void clear() { |
| this.map.clear(); |
| } |
| } |