缓存击穿后单机只用一个线程命中Db策略-蒲公英云

缓存击穿后单机只用一个线程命中Db策略

水深无声 2021-06-12 20:36 287阅读 0赞

private ConcurrentHashMap<Integer, FutureTask<ShopDto> shopTaskMap = new ConcurrentHashMap<Integer, FutureTask<ShopDto>();
public ShopDto loadShop(int shopId) { 
    ShopDto dto = getFromCache(shopId); 
    if (dto == null) { 
        FutureTask<ShopDto> future = shopTaskMap.get(shopId); 
        if (future == null) { 
            FutureTask<ShopDto> task = new FutureTask<ShopDto>(new ShopDBTask(shopId)); 
            future = shopTaskMap.putIfAbsent(shopId, task); 
            if (future == null) { 
                future = task;
                future.run(); //确保本机只有一个线程命中DB
            }
        }
        try { 
             dto = future.get(200, TimeUnit.MILLISECONDS); 
        } catch (Exception e) { 
              return null; 
        } finally { 
            shopTaskMap.remove(shopId);
        } } //end if (dto == null)
     return dto; 
}
class ShopDBTask implements Callable<ShopDto>{ 
    private int shopId; 
    public ShopDBTask (int shopId){ 
        this.shopId = shopId; 
    }
    @Override
    public ShopDto call() throws Exception { 
         ShopDto dto = loadFromDB(shopId);
         if(dto == null){ 
             dto = new ShopDto (); 
         }
        setCache(shopId, ShopDto); 
         return dto; 
    } }