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package org.wowtools.common.utils;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.Map;

import com.googlecode.concurrentlinkedhashmap.ConcurrentLinkedHashMap;
import com.googlecode.concurrentlinkedhashmap.Weighers;

/**
 * 最近最少使用原则LRU(Least recently used)失效的缓存
 *
 * @author liuyu
 */
public class LruCache {

    private static final ArrayList caches = new ArrayList<>(1);

    /**
     * 构建一个Map对象作为缓存容器，当map中对象的容量超过其容量时，将利用LRU(Least recently used)算法淘汰掉不常使用的对象
     *
     * @param capacity    最大容量
     * @param concurrency 预计在运行中会有多少个线程同时对缓存进行更新，若此值大于1，则返回一个ConcurrentLinkedHashMap
     * @return LRU map cache
     */
    public static  Map buildCache(final int capacity, int concurrency) {
        Map res;
        if (concurrency < 2) {
            res = new LinkedHashMap(capacity, 0.75f, true) {
                private static final long serialVersionUID = 1L;

                @Override
                protected boolean removeEldestEntry(java.util.Map.Entry eldest) {
                    return size() > capacity;
                }
            };
        } else {
            res = new ConcurrentLinkedHashMap.Builder().weigher(Weighers.singleton())
                    .initialCapacity(capacity).maximumWeightedCapacity(capacity).concurrencyLevel(concurrency).build();
        }
        synchronized (caches) {
            caches.add(res);
        }
        return res;

    }

    /**
     * 清空所有缓存
     */
    public static void clearAll() {
        synchronized (caches) {
            for (Map cach : caches) {
                cach.clear();
            }
        }
    }

}