LocaleObjectCache.java

/*
 * Copyright (c) 2010, 2011, 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
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/*
 *******************************************************************************
 * Copyright (C) 2009-2010, International Business Machines Corporation and    *
 * others. All Rights Reserved.                                                *
 *******************************************************************************
 */
package sun.util.locale;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

public abstract class LocaleObjectCache<K, V> {
    private ConcurrentMap<K, CacheEntry<K, V>> map;
    private ReferenceQueue<V> queue = new ReferenceQueue<>();

    public LocaleObjectCache() {
        this(16, 0.75f, 16);
    }

    public LocaleObjectCache(int initialCapacity, float loadFactor, int concurrencyLevel) {
        map = new ConcurrentHashMap<>(initialCapacity, loadFactor, concurrencyLevel);
    }

    public V get(K key) {
        V value = null;

        cleanStaleEntries();
        CacheEntry<K, V> entry = map.get(key);
        if (entry != null) {
            value = entry.get();
        }
        if (value == null) {
            V newVal = createObject(key);
            // make sure key is normalized *after* the object creation
            // so that newVal is assured to be created from a valid key.
            key = normalizeKey(key);
            if (key == null || newVal == null) {
                // subclass must return non-null key/value object
                return null;
            }

            CacheEntry<K, V> newEntry = new CacheEntry<>(key, newVal, queue);

            entry = map.putIfAbsent(key, newEntry);
            if (entry == null) {
                value = newVal;
            } else {
                value = entry.get();
                if (value == null) {
                    map.put(key, newEntry);
                    value = newVal;
                }
            }
        }
        return value;
    }

    protected V put(K key, V value) {
        CacheEntry<K, V> entry = new CacheEntry<>(key, value, queue);
        CacheEntry<K, V> oldEntry = map.put(key, entry);
        return (oldEntry == null) ? null : oldEntry.get();
    }

    @SuppressWarnings("unchecked")
    private void cleanStaleEntries() {
        CacheEntry<K, V> entry;
        while ((entry = (CacheEntry<K, V>)queue.poll()) != null) {
            map.remove(entry.getKey());
        }
    }

    protected abstract V createObject(K key);

    protected K normalizeKey(K key) {
        return key;
    }

    private static class CacheEntry<K, V> extends SoftReference<V> {
        private K key;

        CacheEntry(K key, V value, ReferenceQueue<V> queue) {
            super(value, queue);
            this.key = key;
        }

        K getKey() {
            return key;
        }
    }
}