HttpContext.Current.Cache和HttpRuntime.Cache的区别，以及System.Runtime.Caching

using System;
using System.Collections;
using System.Web;
using System.Web.Caching;

namespace aaaaa.Api.Business
{
    /// <summary>
    /// 缓存类
    /// </summary>
    public class CacheHelper
    {
        /// <summary>
        /// 增加一个缓存对象
        /// </summary>
        /// <param name="strKey">键值名称</param>
        /// <param name="valueObj">被缓存对象</param>
        /// <param name="durationMin">缓存失效时间（默认为5分钟）</param>
        /// <param name="cachePriority">保留优先级(枚举数值)</param>
        /// <returns>缓存写入是否成功true 、false</returns>
        public static bool InsertCach(string strKey, object valueObj, int durationMin,
            CacheItemPriority cachePriority = CacheItemPriority.Default)
        {
            TimeSpan ts;
            if (!string.IsNullOrWhiteSpace(strKey) && valueObj != null)
            {
                //onRemove是委托执行的函数，具体方法看下面的onRemove(...)
                CacheItemRemovedCallback callBack = new CacheItemRemovedCallback(onRemove);
                ts = durationMin == 0 ? new TimeSpan(0, 5, 0) : new TimeSpan(0, durationMin, 0);
                //HttpContext.Current.Cache.Insert(
                HttpRuntime.Cache.Insert(
                    strKey,
                    valueObj,
                    null,
                    DateTime.Now.Add(ts),
                    Cache.NoSlidingExpiration,
                    cachePriority,
                    callBack
                );
                return true;
            }
            else
            {
                return false;
            }
        }

        /// <summary>
        /// 判断缓存对象是否存在
        /// </summary>
        /// <param name="strKey">缓存键值名称</param>
        /// <returns>是否存在true 、false</returns>
        public static bool IsExist(string strKey)
        {
            //return HttpContext.Current.Cache[strKey] != null;
            return HttpRuntime.Cache.Get(strKey) != null;
        }

        /// <summary>
        /// 读取缓存对象
        /// </summary>
        /// <param name="strKey">缓存键值名称</param>
        /// <returns>缓存对象，objec类型</returns>
        public static object GetCache(string strKey)
        {
            //if (HttpContext.Current.Cache[strKey] != null)
            if (IsExist(strKey))
            {
                object obj = HttpRuntime.Cache.Get(strKey);
                return obj ?? null;
            }
            else
            {
                return null;
            }
        }

        /// <summary>
        /// 移除缓存对象
        /// </summary>
        /// <param name="strKey">缓存键值名称</param>
        public static void Remove(string strKey)
        {
            //if (HttpContext.Current.Cache[strKey] != null)
            if (IsExist(strKey))
            {
                HttpRuntime.Cache.Remove(strKey);
            }
        }

        /// <summary>
        /// 清除所有缓存
        /// </summary>
        public static void Clear()
        {
            IDictionaryEnumerator enu = HttpRuntime.Cache.GetEnumerator();
            while (enu.MoveNext())
            {
                Remove(enu.Key.ToString());
            }
        }

        public static CacheItemRemovedReason reason;
        /// <summary>
        /// 此方法在值失效之前调用，可以用于在失效之前更新数据库，或从数据库重新获取数据
        /// </summary>
        /// <param name="strKey"></param>
        /// <param name="obj"></param>
        /// <param name="reason"></param>
        private static void onRemove(string strKey, object obj, CacheItemRemovedReason r)
        {
            reason = r;
        }

        //...

    }
}

static void CacheTest()
        {
            string cname = "filescontents";
            ObjectCache cc = MemoryCache.Default;
            string fileContents = cc[cname] as string;

            if (fileContents == null)
            {
                CacheItemPolicy policy = new CacheItemPolicy();

                TimeSpan sp = new TimeSpan(0, 1, 0);
                policy.SlidingExpiration = sp;

                List<string> filePaths = new List<string>();
                string path = System.IO.Directory.GetCurrentDirectory() + "\\example.txt";
                filePaths.Add(path);

                policy.ChangeMonitors.Add(new HostFileChangeMonitor(filePaths));

                fileContents = System.IO.File.ReadAllText(path, Encoding.Default);
                cc.Set(cname, fileContents, policy);
            }

            Console.WriteLine(fileContents);
        }


static void Main(string[] args)
        {
            //ExecuteCode(WriteData);
            //ExecuteCode(ReadData);
            //ExecuteCode(TransData);
            bool quit = false;
            while (!quit)
            {
                Console.Write("get cache: ");
                string demo = Console.ReadLine();
                switch (demo)
                {
                    case "Y": ExecuteCode(CacheTest); break;
                    case "Q":
                        quit = true;
                        break;
                    default:
                        Console.WriteLine("Choose a Word of Y and Q(to quit)");
                        break;
                }
            }
            Console.ReadKey();
        }

        public static void ExecuteCode(Action a)
        {
            System.Diagnostics.Stopwatch stopwatch = new System.Diagnostics.Stopwatch();
            stopwatch.Start();

            a();

            stopwatch.Stop();
            TimeSpan timespan = stopwatch.Elapsed;

            Console.WriteLine("运行{0}秒", timespan.TotalSeconds);
        }