一个文件修改后，缓存也重新加载，缓存依赖(文件)

 protected void Page_Load(object sender,EventArgs e)
    {


        if (Cache["Msg"] == null)
        {
            string filepath = Server.MapPath("~/CacheHot.txt");
            string content = System.IO.File.ReadAllText(filepath);
            System.Web.Caching.CacheDependency dency = new System.Web.Caching.CacheDependency(filepath);
            //Cache.Insert("Msg",content,dency,System.Web.Caching.Cache.NoAbsoluteExpiration,System.Web.Caching.Cache.NoSlidingExpiration,new System.Web.Caching.CacheItemRemovedCallback(callback));
            //键，值，依赖对象，绝对过期，滑动过期，优先级，当删除时，回调函数
Cache.Insert("Msg",DateTime.Now.ToString(),CacheItemPriority.Normal,callback);
        }
        else {
            Response.Write(Cache["Msg"].ToString());
        }

    }

    public void callback(string key,object value,CacheItemRemovedReason reason)
    {
        string filepath = Server.MapPath("~/CacheLog.txt");
        string content = "Cache["+key+"]="+value.ToString()+"被删除 了"+reason.ToString();
        System.IO.File.AppendAllText(filepath,content);
    }
}