负载均衡环境下，Web应用的缓存管理

bsp;   {
            return null;
        }

        protected virtual void OnBeforeAdd(string key)
        {
        }
        
        public virtual void Add(string key, object value)
        {
            if (!this.CheckParameters(key)) return;
            this.OnBeforeAdd(key);
            HttpRuntime.Cache.Insert(
                key,
                value,
                this.GetCacheDependency(key),
                System.Web.Caching.Cache.NoAbsoluteExpiration,
                System.Web.Caching.Cache.NoSlidingExpiration,
                System.Web.Caching.CacheItemPriority.Default,
                null);
        }

        public virtual object Get(string key)
        {
            if (!this.CheckParameters(key)) return null;
            return HttpRuntime.Cache.Get(key);
        }

        public virtual void Remove(string key, bool useDependency)
        {
            if (!this.CheckParameters(key)) return;
            HttpRuntime.Cache.Remove(key);
        }
    }

    public class SqlDependencyWebCache : WebCacheBase
    {
        private string _connectionString;

        priva