//獲取鎖
private boolean tryLock(String key) {
    Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", 10, TimeUnit.SECONDS);
    return BooleanUtil.isTrue(flag);
}

//釋放鎖
private void unLock(String key) {
    stringRedisTemplate.delete(key);
}

@Override
public Result queryById(Long id) {
    //緩存空對(duì)象解決 緩存穿透
    //Shop shop = queryWithPassThrough(id);

    //互斥鎖解決 緩存擊穿
    Shop shop = queryWithMutex(id);
    if (shop == null) {
        return Result.fail("店鋪不存在！");
    }
    return Result.ok(shop);
}

public Shop queryWithMutex(Long id) {
    //1.從redis查詢商鋪緩存
    String key = CACHE_SHOP_KEY + id;
    String shopJson = stringRedisTemplate.opsForValue().get(key);
    //2.判斷是否存在
    if (StrUtil.isNotBlank(shopJson)) {
        //3.存在，直接返回
        return JSONUtil.toBean(shopJson, Shop.class);
    }
    //此時(shí) shopJson 不是為null就是為""
    if (shopJson != null) {
        //為""直接返回錯(cuò)誤信息，為null查詢數(shù)據(jù)庫
        return null;
    }

    //4.實(shí)現(xiàn)緩存重建
    //4.1.獲取互斥鎖
    String lockKey = "lock:shop:" + id;
    Shop shop = null;
    try {
        boolean isLock = tryLock(lockKey);
        //4.2.判斷是否獲取成功
        while (!isLock) {
            //4.3.失敗，則休眠重試
            Thread.sleep(50);
            return queryWithMutex(id);
        }
        //4.4.獲取鎖成功，再次檢測緩存釋放存在(double check)
        String cacheShopJson = stringRedisTemplate.opsForValue().get(key);
        if (StrUtil.isNotBlank(cacheShopJson)) {
            //4.5.存在，直接返回
            return JSONUtil.toBean(cacheShopJson, Shop.class);
        }
        //5.緩存數(shù)據(jù)不存在，根據(jù)id查詢數(shù)據(jù)庫
        shop = getById(id);
        //模擬重建的延時(shí)
        Thread.sleep(200);
        //6.不存在，返回錯(cuò)誤
        if (shop == null) {
            //緩存空值
            stringRedisTemplate.opsForValue().set(key, "", CACHE_NULL_TTL, TimeUnit.MINUTES);
            return null;
        }
        //7.存在，寫入redis
        stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(shop), CACHE_SHOP_TTL, TimeUnit.MINUTES);
    } catch (InterruptedException e) {
        throw new RuntimeException(e);
    } finally {
        //8.釋放鎖
        unLock(lockKey);
    }
    return shop;
}

@Data
public class RedisData {
    private LocalDateTime expireTime;
    private Object data;
}

private static final ExecutorService CACHE_REBUILD_EXECUTOR = Executors.newFixedThreadPool(10);

public void saveShop2Redis(Long id, Long expireSeconds) throws InterruptedException {
    //1.查詢店鋪數(shù)據(jù)
    Shop shop = getById(id);
    //2.封裝邏輯過期時(shí)間
    RedisData redisData = new RedisData();
    redisData.setData(shop);
    //設(shè)置邏輯過期時(shí)間
    redisData.setExpireTime(LocalDateTime.now().plusSeconds(expireSeconds));
    stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, JSONUtil.toJsonStr(redisData));
}

@Override
public Result queryById(Long id) {
    //緩存空對(duì)象解決 緩存穿透
    //Shop shop = queryWithPassThrough(id);

    //互斥鎖解決 緩存擊穿
    //Shop shop = queryWithMutex(id);

    //邏輯過期解決 緩存擊穿
    Shop shop = queryWithLogicalExpire(id);
    if (shop == null) {
        return Result.fail("店鋪不存在！");
    }
    return Result.ok(shop);
}

public Shop queryWithLogicalExpire(Long id) {
    //1.從redis查詢商鋪緩存
    String key = CACHE_SHOP_KEY + id;
    String shopJson = stringRedisTemplate.opsForValue().get(key);
    //2.判斷是否存在
    if (StrUtil.isBlank(shopJson)) {
        //未命中，直接返回空
        return null;
    }
    //3.命中，判斷是否過期
    RedisData redisData = JSONUtil.toBean(shopJson, RedisData.class);
    Shop cacheShop = JSONUtil.toBean((JSONObject) redisData.getData(), Shop.class);
    if (redisData.getExpireTime().isAfter(LocalDateTime.now())) {
        //3.1未過期,直接返回店鋪信息
        return cacheShop;
    }
    //3.2.已過期，緩存重建
    //3.3.獲取鎖
    String lockKey = LOCK_SHOP_KEY + id;
    boolean flag = tryLock(lockKey);
    if (flag) {
        //3.4.獲取成功
        //4再次檢查redis緩存是否過期，做double check
        shopJson = stringRedisTemplate.opsForValue().get(key);
        //4.1.判斷是否存在
        if (StrUtil.isBlank(shopJson)) {
            //未命中，直接返回空
            return null;
        }
        //4.2.命中，判斷是否過期
        redisData = JSONUtil.toBean(shopJson, RedisData.class);
        cacheShop = JSONUtil.toBean((JSONObject) redisData.getData(), Shop.class);
        if (redisData.getExpireTime().isAfter(LocalDateTime.now())) {
            //4.3.未過期,直接返回店鋪信息
            return cacheShop;
        }
        CACHE_REBUILD_EXECUTOR.submit(() -> {
            //5.重建緩存
            try {
                this.saveShop2Redis(id, 20L);
            } catch (Exception e) {
                throw new RuntimeException(e);
            } finally {
                //釋放鎖
                unLock(lockKey);
            }
        });
    }
    //7.獲取失敗,返回舊數(shù)據(jù)
    return cacheShop;
}