指定次数或者缓存过期时更新数据库

using System;
using System.Collections.Generic;
using System.Text;
using System.Web.Caching;
using System.Web;
using System.Data;
using System.Data.SqlClient;

namespace TGBUS.Count
{
    public class TGBUS_Handler : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {
            int _pid = 0;
            try
            {
                if (context.Request.QueryString["pid"] != null && context.Request.QueryString["pid"].ToString() != "")
                {
                    _pid = Convert.ToInt32(context.Request.QueryString["pid"].ToString());
                }
                CounterHelper objCounterHelper = new CounterHelper(_pid.ToString());
                objCounterHelper.AddHits();
                //context.Response.Write(string.Format("document.write('nums:{0}  id:{1}')", objCounterHelper.AllHits,context.Request.Url.AbsoluteUri));

            }
            catch(Exception ex)
            { }
        }

        public bool IsReusable
        {
            get
            {
                return true;
            }
        }

    }

    #region 统计类
    public class CounterHelper
    {
        public int _Hits = 0; //累计的点击数
        private static int _HitsAll = 0;
        private int ProductId = 0;
        private string CacheName = "TGBUS_Hits";//缓存名称
        private object LockForAddHits = new object();//LockForAddHits锁
        private object LockForItemRemovedFromCacheHits = new object();//ItemRemovedFromCacheHits锁
        CacheItemRemovedCallback onRemove = null;//CacheItemRemovedCallback对象

        /**/
        /// <summary>
        /// 构造函数
        /// </summary>
        public CounterHelper(string _ProductId)
        {
            CacheName = CacheName + _ProductId;
            ProductId = Convert.ToInt32(_ProductId);
            HttpContext ctx = HttpContext.Current;
            LoadHits();
        }
        /// <summary>
        /// 加载点击数
        /// </summary>
        private void LoadHits()
        {
            if (HttpRuntime.Cache[CacheName] == null)
            {
                _Hits = 0;
            }
            else
            {
                _Hits = Convert.ToInt32(HttpRuntime.Cache["_temp" + CacheName].ToString());
            }
        }
        /// <summary>
        /// 将累计点击数保存到全局变量，当它达到一定量时保存到文本文件，并清空
        /// </summary>
        public void AddHits()
        {
            lock (LockForAddHits)
            {
                if (HttpRuntime.Cache[CacheName] != null)
                {
                    Add();
                    _HitsAll = Hits;
                    if (Hits > 500)
                    {
                        //--移除        
                                      
                        HttpRuntime.Cache.Remove(CacheName);
                    }
                }
                else
                {
                    onRemove = new CacheItemRemovedCallback(ItemRemovedFromCache);
                    HttpRuntime.Cache.Insert(
                        CacheName,
                        "This Object For Expired",
                        null,
                        DateTime.Now.AddSeconds(20),
                        TimeSpan.Zero,
                        System.Web.Caching.CacheItemPriority.Normal,
                        onRemove
                        );
                    Add();
                    _HitsAll = Hits;
                }
            }
        }

        /**/
        /// <summary>
        /// 当缓存被移除或过期是触发的回调事件
        /// </summary>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="reason"></param>
        private void ItemRemovedFromCache(string key, object value, CacheItemRemovedReason reason)
        {
            try
            {
                #region 清空并写到数据库
                int hits = 0;
                lock (LockForItemRemovedFromCacheHits)
                {
                    hits = _HitsAll;
                }
                if (hits == 0)
                {
                    return;
                }
                else
                {
                    SaveHits(hits);
                }
                #endregion
            }
            catch (Exception ex)
            {

            }
        }

        /// <summary>
        /// 保存点击数
        /// </summary>
        /// <param name="hits"></param>
        private void SaveHits(int hits)
        {
            string _Sql = "Update dbo].[Product] set [ViewsCount] = [ViewsCount]+" + hits + " where [ProductId]='" + ProductId + "'";
            TGBUS.DBUtility.SqlHelper.ExecuteNonQuery(TGBUS.DBUtility.SqlHelper.connectionString, CommandType.Text, _Sql);
        }

        /// <summary>
        /// 累加点击数
        /// </summary>
        private void Add()
        {
            _Hits = _Hits + 1;
            HttpRuntime.Cache["_temp" + CacheName] = _Hits;
        }
        //// <summary>
        /// 获取所有的点击数
        /// </summary>
        public int AllHits
        {
            get
            {
                return Hits;
            }
        }

        /**/
        /// <summary>
        /// 获取累计的点击数
        /// </summary>
        private int Hits
        {
            get { return _Hits; }
            set { _Hits = value; }
        }
    }
    #endregion
}