InMemoryCache.cs

 public T GetOrSet<T>(string cacheKey, Func<T> getItemCallback) where T : class
        {
            T item = MemoryCache.Default.Get(cacheKey) as T;

            int duration;

            if (ConfigurationManager.AppSettings["InMemoryCacheDuration"] == null ||
                !Int32.TryParse(ConfigurationManager.AppSettings["InMemoryCacheDuration"], out duration))
                duration = 30;

            if (item != null) return item;

            var slidingExpirationPolicy = new CacheItemPolicy()
            {
                SlidingExpiration = new TimeSpan(0, duration, 0)
            };

            item = getItemCallback();
            MemoryCache.Default.Add(cacheKey, item, slidingExpirationPolicy);
            return item;
        }
    }

    interface ICacheService
    {
        T GetOrSet<T>(string cacheKey, Func<T> getItemCallback) where T : class;
    }