并发编程中的ConcurrentHashMap

import lombok.Data;
 
import java.io.Serializable;
 
/**
 * 缓存
 */
@Data
public class CacheObj implements Serializable {
    private static final long serialVersionUID = 5272376851165037333L;
    /**
     * 缓存对象
     */
    private Object cacheValue;
    /**
     * 缓存过期时间
     */
    private Long ttlTime;
 
    public CacheObj(Object cacheValue, Long ttlTime) {
        this.cacheValue = cacheValue;
        this.ttlTime = ttlTime;
    }
 
    @Override
    public String toString() {
        return "CacheObj {" +
                "cacheValue = " + cacheValue +
                ", ttlTime = " + ttlTime +
                '}';
    }
}

 
import lombok.extern.slf4j.Slf4j;
 
/**
 * 每一分钟清理一次过期缓存
 */
@Slf4j
public class CleanTimeOutThread implements Runnable {
    @Override
    public void run() {
        ConcurrentHashMapCacheUtil.setCleanThreadRun();
        while (true) {
            log.warn("clean thread run ");
            ConcurrentHashMapCacheUtil.deleteTimeOut();
            try {
                Thread.sleep(ConcurrentHashMapCacheUtil.ONE_MINUTE);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
 
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
 
/**
 * 本地缓存
 */
@Slf4j
@Component
public class ConcurrentHashMapCacheUtil {
    /**
     * 缓存最大个数
     */
    private static final Integer CACHE_MAX_NUMBER = 50000;
    /**
     * 当前缓存个数
     */
    private static Integer CURRENT_SIZE = 0;
    /**
     * 时间一分钟
     */
    static final Long ONE_MINUTE = 60 * 1000L;
    /**
     * 永不过期
     */
    private static final Long CACHE_FOREVER = -1L;
    /**
     * 缓存对象
     */
    private static final Map<String, CacheObj> CACHE_OBJECT_MAP = new ConcurrentHashMap();
    /**
     * 这个记录了缓存使用的最后一次的记录，最近使用的在最前面
     */
    private static final List<String> CACHE_USE_LOG_LIST = new LinkedList();
    /**
     * 清理过期缓存是否在运行
     */
    private static volatile Boolean CLEAN_THREAD_IS_RUN = false;
 
 
    /**
     * 设置缓存
     *
     * @param cacheKey
     * @param cacheValue
     * @param cacheTime
     */
    public static void setCache(String cacheKey, Object cacheValue, long cacheTime) {
        Long ttlTime = null;
        if (cacheTime <= 0L) {
            if (cacheTime == -1L) {
                ttlTime = -1L;
            } else {
                return;
            }
        }
//        checkSize();
//        saveCacheUseLog(cacheKey);
        CURRENT_SIZE = CURRENT_SIZE + 1;
        if (ttlTime == null) {
            ttlTime = System.currentTimeMillis() + cacheTime;
        }
        CacheObj cacheObj = new CacheObj(cacheValue, ttlTime);
        CACHE_OBJECT_MAP.put(cacheKey, cacheObj);
        log.info("have set key :{}", cacheKey);
    }
 
    /**
     * 设置缓存
     *
     * @param cacheKey
     * @param cacheValue
     */
    public static void setCache(String cacheKey, Object cacheValue) {
        setCache(cacheKey, cacheValue, CACHE_FOREVER);
    }
 
    /**
     * 获取缓存
     *
     * @param cacheKey
     * @return
     */
    public static Object getCache(String cacheKey) {
//        startCleanThread();
        if (checkCache(cacheKey)) {
            saveCacheUseLog(cacheKey);
            return CACHE_OBJECT_MAP.get(cacheKey).getCacheValue();
        }
        return null;
    }
 
    public static boolean isExist(String cacheKey) {
        return checkCache(cacheKey);
    }
 
    /**
     * 删除所有缓存
     */
    public static void clear() {
        log.info("have clean all key !");
        CACHE_OBJECT_MAP.clear();
        CURRENT_SIZE = 0;
    }
 
    /**
     * 删除单个缓存
     *
     * @param cacheKey
     */
    public static void deleteCache(String cacheKey) {
        Object cacheValue = CACHE_OBJECT_MAP.remove(cacheKey);
        if (cacheValue != null) {
            log.info("have delete key : {}", cacheKey);
            CURRENT_SIZE = CURRENT_SIZE - 1;
        }
    }
 
    /**
     * 判断缓存在不在,过没过期
     *
     * @param cacheKey
     * @return
     */
    private static boolean checkCache(String cacheKey) {
        CacheObj cacheObj = CACHE_OBJECT_MAP.get(cacheKey);
        if (cacheObj == null) {
            return false;
        }
        if (cacheObj.getTtlTime() == -1L) {
            return true;
        }
        if (cacheObj.getTtlTime() < System.currentTimeMillis()) {
            deleteCache(cacheKey);
            return false;
        }
        return true;
    }
 
    /**
     * 删除最近最久未使用的缓存
     */
    private static void deleteLRU() {
        log.info("delete Least recently used run!");
        String cacheKey = null;
        synchronized (CACHE_USE_LOG_LIST) {
            if (CACHE_USE_LOG_LIST.size() >= CACHE_MAX_NUMBER - 10) {
                cacheKey = CACHE_USE_LOG_LIST.remove(CACHE_USE_LOG_LIST.size() - 1);
            }
        }
        if (cacheKey != null) {
            deleteCache(cacheKey);
        }
    }
 
    /**
     * 删除过期的缓存
     */
    public static void deleteTimeOut() {
        log.info("delete time out run!");
        List<String> deleteKeyList = new LinkedList<>();
        for (Map.Entry<String, CacheObj> entry : CACHE_OBJECT_MAP.entrySet()) {
            if (entry.getValue().getTtlTime() < System.currentTimeMillis() && entry.getValue().getTtlTime() != -1L) {
                deleteKeyList.add(entry.getKey());
            }
        }
 
        for (String deleteKey : deleteKeyList) {
            deleteCache(deleteKey);
        }
        log.info("delete cache count is :{}", deleteKeyList.size());
 
    }
 
    /**
     * 检查大小
     * 当当前大小如果已经达到最大大小
     * 首先删除过期缓存，如果过期缓存删除过后还是达到最大缓存数目
     * 删除最久未使用缓存
     */
    private static void checkSize() {
        if (CURRENT_SIZE >= CACHE_MAX_NUMBER) {
            deleteTimeOut();
        }
        if (CURRENT_SIZE >= CACHE_MAX_NUMBER) {
            deleteLRU();
        }
    }
 
    /**
     * 保存缓存的使用记录
     *
     * @param cacheKey
     */
    private static synchronized void saveCacheUseLog(String cacheKey) {
        synchronized (CACHE_USE_LOG_LIST) {
            CACHE_USE_LOG_LIST.remove(cacheKey);
            CACHE_USE_LOG_LIST.add(0, cacheKey);
        }
    }
 
    /**
     * 设置清理线程的运行状态为正在运行
     */
    public static void setCleanThreadRun() {
        CLEAN_THREAD_IS_RUN = true;
    }
 
    /**
     * 开启清理过期缓存的线程
     */
    private static void startCleanThread() {
        if (!CLEAN_THREAD_IS_RUN) {
            CleanTimeOutThread cleanTimeOutThread = new CleanTimeOutThread();
            Thread thread = new Thread(cleanTimeOutThread);
            //设置为后台守护线程
            thread.setDaemon(true);
            thread.start();
        }
    }
}