org.structr.api.util.FixedSizeCache.java Source code

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Here is the source code for org.structr.api.util.FixedSizeCache.java

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/**
 * Copyright (C) 2010-2018 Structr GmbH
 *
 * This file is part of Structr <http://structr.org>.
 *
 * Structr is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * Structr 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 for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Structr.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.structr.api.util;

import java.util.Collection;
import java.util.Collections;
import java.util.Map;
import org.apache.commons.collections4.map.LRUMap;

/**
 * A map-like storage structure with a fixed maximum size that
 * removes the least recently used entry when the insertion of
 * a new entry causes the map to exceed the specified maximum
 * size.
 *
 * @param <K>
 * @param <V>
 */
public class FixedSizeCache<K, V> {

    private Map<K, V> cache = null;

    public FixedSizeCache(final int maxSize) {
        this.cache = Collections.synchronizedMap(new InvalidatingLRUMap<>(maxSize));
    }

    public synchronized void put(final K key, final V value) {
        cache.put(key, value);
    }

    public synchronized V get(final K key) {
        return cache.get(key);
    }

    public synchronized void removeAll(final Collection<K> keys) {
        cache.keySet().removeAll(keys);
    }

    public synchronized void remove(final K key) {
        cache.remove(key);
    }

    public synchronized void clear() {
        cache.clear();
    }

    public synchronized int size() {
        return cache.size();
    }

    public synchronized boolean isEmpty() {
        return cache.isEmpty();
    }

    private static class InvalidatingLRUMap<K, V> extends LRUMap<K, V> {

        public InvalidatingLRUMap(final int maxSize) {
            super(maxSize, true);
        }

        @Override
        protected boolean removeLRU(final LinkEntry<K, V> entry) {

            final V value = entry.getValue();
            if (value != null && value instanceof Cachable) {

                ((Cachable) value).onRemoveFromCache();
            }

            return true;
        }
    }
}