com.sitewhere.common.ExpiringLRUCache.java Source code

Introduction

Here is the source code for com.sitewhere.common.ExpiringLRUCache.java

Source

/*
 * Copyright (c) SiteWhere, LLC. All rights reserved. http://www.sitewhere.com
 *
 * The software in this package is published under the terms of the CPAL v1.0
 * license, a copy of which has been included with this distribution in the
 * LICENSE.txt file.
 */
package com.sitewhere.common;

import java.util.Collections;
import java.util.Date;
import java.util.Map;

import org.apache.commons.collections.map.LRUMap;

/**
 * Extends {@link LRUMap} with an expiration check.
 * 
 * @author Derek
 * 
 * @param <K>
 * @param <V>
 */
public class ExpiringLRUCache<K, V> {

    /** Default expiration period in milliseconds */
    private static final int DEFAULT_EXPIRATION = 30 * 1000;

    /** Hashmap for storage */
    private Map<K, CacheEntry<V>> map;

    /** Entry expiration time in milliseconds */
    private int expirationInMS = DEFAULT_EXPIRATION;

    /** Cache statistics */
    private CacheStatistics statistics = new CacheStatistics(this);

    @SuppressWarnings("unchecked")
    public ExpiringLRUCache(int size, int expirationInMs) {
        map = Collections.synchronizedMap(new LRUMap(size));
        this.expirationInMS = expirationInMs;
    }

    /**
     * Add a new entry to the cache. Removes any existing entry.
     * 
     * @param key
     * @param value
     */
    public void put(K key, V value) {
        CacheEntry<V> entry = new CacheEntry<V>(new Date(), value);
        map.put(key, entry);
    }

    /**
     * Get value if it has not expired.
     * 
     * @param key
     * @return
     */
    public V get(K key) {
        CacheEntry<V> entry = map.get(key);
        if (entry == null) {
            return null;
        }
        if ((entry.getTimestamp().getTime() - System.currentTimeMillis()) > expirationInMS) {
            map.remove(key);
            return null;
        }
        return entry.getValue();
    }

    /**
     * Get number of entries in cache.
     * 
     * @return
     */
    public int getSize() {
        return map.size();
    }

    /**
     * Get cache statistics.
     * 
     * @return
     */
    public CacheStatistics getStatistics() {
        return statistics;
    }

    /** Class for cache entry */
    public static class CacheEntry<V> {

        /** Timestamp for expiration check */
        private Date timestamp;

        /** Stored value */
        private V value;

        public CacheEntry(Date timestamp, V value) {
            this.timestamp = timestamp;
            this.value = value;
        }

        public Date getTimestamp() {
            return timestamp;
        }

        public V getValue() {
            return value;
        }
    }

    public static class CacheStatistics {

        /** Cache */
        private ExpiringLRUCache<?, ?> cache;

        /** Number of misses */
        private int cacheMisses = 0;

        /** Number of hits */
        private int cacheHits = 0;

        public CacheStatistics(ExpiringLRUCache<?, ?> cache) {
            this.cache = cache;
        }

        public void hit() {
            cacheHits++;
        }

        public void miss() {
            cacheMisses++;
        }

        public int getCacheSize() {
            return cache.getSize();
        }

        public int getCacheMisses() {
            return cacheMisses;
        }

        public int getCacheHits() {
            return cacheHits;
        }

        public double getHitRatio() {
            if ((cacheHits + cacheMisses) == 0) {
                return 0.0;
            }
            return cacheHits / (cacheHits + cacheMisses);
        }

        public String toString() {
            return "Hits: " + getCacheHits() + " Misses: " + getCacheMisses() + " Ratio: " + getHitRatio();
        }
    }
}