SoftReferenceCacheEntry.java

/**
 * This file is part of Waarp Project.
 * 
 * Copyright 2009, Frederic Bregier, and individual contributors by the @author tags. See the
 * COPYRIGHT.txt in the distribution for a full listing of individual contributors.
 * 
 * All Waarp Project 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.
 * 
 * Waarp 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 Waarp. If not, see
 * <http://www.gnu.org/licenses/>.
 */
package org.waarp.common.lru;

import java.lang.ref.SoftReference;

/**
 * Cache entry which uses SoftReference to store value
 * 
 * @author Frederic Bregier
 * @author Damian Momot
 */
class SoftReferenceCacheEntry<V> implements InterfaceLruCacheEntry<V> {

    private final SoftReference<V> valueReference;

    private long expirationTime;

    /**
     * Creates LruCacheEntry with desired ttl
     * 
     * @param value
     * @param ttl
     *            time to live in milliseconds
     * @throws IllegalArgumentException
     *             if ttl is not positive
     */
    SoftReferenceCacheEntry(V value, long ttl) {
        if (ttl <= 0)
            throw new IllegalArgumentException("ttl must be positive");

        valueReference = new SoftReference<V>(value);
        expirationTime = System.currentTimeMillis() + ttl;
    }

    /**
     * Returns value if entry is valid, null otherwise.
     * 
     * Entry is invalid if SoftReference is cleared or entry has expired
     * 
     * @return value if entry is valid
     */
    public V getValue() {
        V value = null;

        // check expiration time
        if (System.currentTimeMillis() <= expirationTime) {
            value = valueReference.get();

            // if (value == null)
            // logger.warn("SoftReferency.get() returned null - probably JVM runs out of memory");
        }

        return value;
    }

    public boolean isStillValid(long timeRef) {
        return (timeRef <= expirationTime);
    }

    public boolean resetTime(long ttl) {
        expirationTime = System.currentTimeMillis() + ttl;
        return true;
    }
}