/* * 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(); }}
/*
* 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();
}
}