001/*
002 * This library is part of OpenCms -
003 * the Open Source Content Management System
004 *
005 * Copyright (c) Alkacon Software GmbH & Co. KG (https://www.alkacon.com)
006 *
007 * This library is free software; you can redistribute it and/or
008 * modify it under the terms of the GNU Lesser General Public
009 * License as published by the Free Software Foundation; either
010 * version 2.1 of the License, or (at your option) any later version.
011 *
012 * This library is distributed in the hope that it will be useful,
013 * but WITHOUT ANY WARRANTY; without even the implied warranty of
014 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
015 * Lesser General Public License for more details.
016 *
017 * For further information about Alkacon Software, please see the
018 * company website: https://www.alkacon.com
019 *
020 * For further information about OpenCms, please see the
021 * project website: https://www.opencms.org
022 *
023 * You should have received a copy of the GNU Lesser General Public
024 * License along with this library; if not, write to the Free Software
025 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
026 */
027
028package org.opencms.util;
029
030/**
031 * Simple utility class for caching a single value with a given cache expiration time.<p>
032 *
033 * If the time between the last write operation and a read operation is longer than the expiration time,
034 * null will be returned from the read operation.<p>
035 *
036 * @param <T> the type of the cached value
037 */
038public class CmsExpiringValue<T> {
039
040    /** The cached value. */
041    private T m_value;
042
043    /** Last time the value was set. */
044    private long m_lastUpdate;
045
046    /** The expiration time. */
047    private long m_expirationTime;
048
049    /**
050     * Creates a new instance.<p>
051     *
052     * @param expirationTime the expiration time in milliseconds
053     */
054    public CmsExpiringValue(long expirationTime) {
055
056        m_expirationTime = expirationTime;
057    }
058
059    /**
060     * Gets the cached value.<p>
061     *
062     * Returns null if the last update was longer ago than the expiration time.
063     *
064     * @return the cached value
065     */
066    public synchronized T get() {
067
068        if ((System.currentTimeMillis() - m_lastUpdate) > m_expirationTime) {
069            return null;
070        }
071        return m_value;
072    }
073
074    /**
075     * Sets the cached value.<p>
076     *
077     * @param value the cached value
078     */
079    public synchronized void set(T value) {
080
081        m_lastUpdate = System.currentTimeMillis();
082        m_value = value;
083    }
084
085}