package com.adingxiong.cft.entity;

import java.io.Serializable;

/**
 * @author xiongc
 * @date 2020/07/28
 */
public class CacheEntity implements Serializable {
    private static final long serialVersionUID = -107853226360392750L;
    /**
     * 值
     */
    private Object value;

    /**
     * 保存的时间戳
     */
    private long gmtModify;

    /**
     * 过期时间
     */
    private int expire;

    public Object getValue() {
        return value;
    }

    public void setValue(Object value) {
        this.value = value;
    }

    public long getGmtModify() {
        return gmtModify;
    }

    public void setGmtModify(long gmtModify) {
        this.gmtModify = gmtModify;
    }

    public int getExpire() {
        return expire;
    }

    public void setExpire(int expire) {
        this.expire = expire;
    }

    public CacheEntity(Object value, long gmtModify, int expire) {
        super();
        this.value = value;
        this.gmtModify = gmtModify;
        this.expire = expire;
    }
}

package com.adingxiong.cft.cache;

import com.adingxiong.cft.entity.CacheEntity;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.util.CollectionUtils;

import java.io.*;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;

/**
 * @ClassName LocalCache
 * @Description 本地缓存 代替redis  实现简单数据记录
 * @Author xiongchao
 * @Date 2020/7/28 16:14
 **/
public class LocalCache {

    private static final Logger log = LoggerFactory.getLogger(LocalCache.class);

    /**
     * 默认的缓存容量
     */
    private static final int DEFAULT_CAPACITY = 512;
    /**
     * 最大容量
     */
    private static final int MAX_CAPACITY = 100000;
    /**
     * 刷新缓存的频率
     */
    private static final int MONITOR_DURATION = 2;

    // 启动监控线程
    static {
        new Thread(new TimeoutTimerThread()).start();
    }

    // 内部类方式实现单例
    private static class LocalCacheInstance{
        private static final LocalCache INSTANCE=new LocalCache();

    }
    public static LocalCache getInstance() {
        return LocalCacheInstance.INSTANCE;
    }

    private LocalCache() {
    }

    /**
     * 使用默认容量创建一个Map
     */
    private static Map<String, CacheEntity> cache = new ConcurrentHashMap<>(DEFAULT_CAPACITY);

    /**
     * 将key-value 保存到本地缓存并制定该缓存的过期时间
     *
     * @param key
     * @param value
     * @param expireTime 过期时间，如果是-1 则表示永不过期
     * @return
     */
    public <T> boolean putValue(String key, T value, int expireTime) {
        return putCloneValue(key, value, expireTime);
    }

    /**
     * 将值通过序列化clone 处理后保存到缓存中，可以解决值引用的问题
     *
     * @param key
     * @param value
     * @param expireTime
     * @return
     */
    private <T> boolean putCloneValue(String key, T value, int expireTime) {
        try {
            if (cache.size() >= MAX_CAPACITY) {
                return false;
            }
            // 序列化赋值
            CacheEntity entityClone = clone(new CacheEntity(value, System.nanoTime(), expireTime));
            cache.put(key, entityClone);
            return true;
        } catch (Exception e) {
            log.error("添加缓存失败：{}", e.getMessage());
        }
        return false;
    }

    /**
     * 序列化 克隆处理
     *
     * @param object
     * @return
     */
    private <E extends Serializable> E clone(E object) {
        E cloneObject = null;
        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ObjectOutputStream oos = new ObjectOutputStream(baos);
            oos.writeObject(object);
            oos.close();
            ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
            ObjectInputStream ois = new ObjectInputStream(bais);
            cloneObject = (E) ois.readObject();
            ois.close();
        } catch (Exception e) {
            log.error("缓存序列化失败：{}", e.getMessage());
        }
        return cloneObject;
    }

    /**
     * 从本地缓存中获取key对应的值，如果该值不存则则返回null
     *
     * @param key
     * @return
     */
    public Object getValue(String key) {
        if(CollectionUtils.isEmpty(cache)){
            return null;
        }
        return cache.get(key).getValue();
    }

    /**
     * 清空所有
     */
    public void clear() {
        cache.clear();
    }

    /**
     * 过期处理线程
     */
    static class TimeoutTimerThread implements Runnable {
        @Override
        public void run() {
            while (true) {
                try {
                    TimeUnit.SECONDS.sleep(MONITOR_DURATION);
                    checkTime();
                } catch (Exception e) {
                    log.error("过期缓存清理失败：{}", e.getMessage());
                }
            }
        }

        /**
         * 过期缓存的具体处理方法
         *
         * @throws Exception
         */
        private void checkTime() throws Exception {
            // 开始处理过期
            for (String key : cache.keySet()) {
                CacheEntity tce = cache.get(key);
                long timoutTime = TimeUnit.NANOSECONDS.toSeconds(System.nanoTime() - tce.getGmtModify());
                // 过期时间 : timoutTime
                if (tce.getExpire() > timoutTime) {
                    continue;
                }
                log.info(" 清除过期缓存 ： " + key);
                //清除过期缓存和删除对应的缓存队列
                cache.remove(key);
            }
        }
    }
}

@GetMapping("/cache")
    public Object testCache(String name){
        Object a = LocalCache.getInstance().getValue("name");
        if(a == null){
            LocalCache.getInstance().putValue("name" ,"张三",10);
            return "未读取到缓存数据";
        }
        return "读取到缓存数据,数据为:" + a;
    }