Java InMemoryCache

Posted 2020-08-07 Googler

package pay.infrastructure.helper;

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

import java.util.ArrayList;

/**
 * Created by wangxiaoming on 2016/3/14.
 */
public class InMemoryCache<TK, TV> {
    protected class CrunchifyCacheObject {
        public long lastAccessed;
        public TV value;

        protected CrunchifyCacheObject(TV value) {
            lastAccessed = System.currentTimeMillis();
            this.value = value;
        }
    }

    private long timeToLive;
    private LRUMap crunchifyCacheMap;

    public InMemoryCache(long crunchifyTimeToLive, final long crunchifyTimerInterval, int maxItems) {
        crunchifyCacheMap = new LRUMap(maxItems);
        this.timeToLive = crunchifyTimeToLive * 1000;

        if (timeToLive > 0 && crunchifyTimerInterval > 0) {
            Thread t = new Thread(new Runnable() {
                public void run() {
                    while (true) {
                        try {
                            Thread.sleep(crunchifyTimerInterval * 1000);
                        } catch (InterruptedException ex) {
                        }
                        cleanup();
                    }
                }
            });
            t.setDaemon(true);
            t.start();
        }
    }

    public void put(TK key, TV value) {
        synchronized (crunchifyCacheMap) {
            crunchifyCacheMap.put(key, new CrunchifyCacheObject(value));
        }
    }

    @SuppressWarnings("unchecked")
    public TV get(TK key) {
        synchronized (crunchifyCacheMap) {
            CrunchifyCacheObject c = (CrunchifyCacheObject) crunchifyCacheMap.get(key);

            if (c == null) {
                return null;
            } else {
                c.lastAccessed = System.currentTimeMillis();
                return c.value;
            }
        }
    }

    public void remove(TK key) {
        synchronized (crunchifyCacheMap) {
            crunchifyCacheMap.remove(key);
        }
    }

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

    @SuppressWarnings("unchecked")
    public void cleanup() {
        long now = System.currentTimeMillis();
        ArrayList<TK> deleteKey = null;

        synchronized (crunchifyCacheMap) {
            MapIterator itr = crunchifyCacheMap.mapIterator();
            deleteKey = new ArrayList<>((crunchifyCacheMap.size() / 2) + 1);

            while (itr.hasNext()) {
                TK key = (TK) itr.next();
                CrunchifyCacheObject c = (CrunchifyCacheObject) itr.getValue();

                if (c != null && (now > (timeToLive + c.lastAccessed))) {
                    deleteKey.add(key);
                }
            }
        }

        for (TK key : deleteKey) {
            synchronized (crunchifyCacheMap) {
                crunchifyCacheMap.remove(key);
            }
            Thread.yield();
        }
    }
}