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