分享基于MemoryCache（内存缓存）的缓存工具类，C# B/S 、C/S项目均可以使用！

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Caching;
using System.Text;
using System.Threading.Tasks;

namespace AutoLogisticsPH.Common.Utils
{
    /// <summary>
    /// 基于MemoryCache（内存缓存）的缓存工具类
    /// Author：左文俊
    /// Date：2017/12/11
    /// </summary>
    public static class MemoryCacheUtil
    {
        private static readonly Object _locker = new object(), _locker2 = new object();

        /// <summary>
        /// 取缓存项，如果不存在则返回空
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <returns></returns>
        public static T GetCacheItem<T>(String key)
        {
            try
            {
                return (T)MemoryCache.Default[key];
            }
            catch
            {
                return default(T);
            }
        }

        /// <summary>
        /// 是否包含指定键的缓存项
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public static bool Contains(string key)
        {
            return MemoryCache.Default.Contains(key);
        }

        /// <summary>
        /// 取缓存项,如果不存在则新增缓存项
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <param name="cachePopulate"></param>
        /// <param name="slidingExpiration"></param>
        /// <param name="absoluteExpiration"></param>
        /// <returns></returns>
        public static T GetOrAddCacheItem<T>(String key, Func<T> cachePopulate, TimeSpan? slidingExpiration = null, DateTime? absoluteExpiration = null)
        {
            if (String.IsNullOrWhiteSpace(key)) throw new ArgumentException("Invalid cache key");
            if (cachePopulate == null) throw new ArgumentNullException("cachePopulate");
            if (slidingExpiration == null && absoluteExpiration == null) throw new ArgumentException("Either a sliding expiration or absolute must be provided");

            if (MemoryCache.Default[key] == null)
            {
                lock (_locker)
                {
                    if (MemoryCache.Default[key] == null)
                    {
                        T cacheValue = cachePopulate();
                        if (!typeof(T).IsValueType && ((object)cacheValue) == null) //如果是引用类型且为NULL则不存缓存
                        {
                            return cacheValue;
                        }

                        var item = new CacheItem(key, cacheValue);
                        var policy = CreatePolicy(slidingExpiration, absoluteExpiration);

                        MemoryCache.Default.Add(item, policy);
                    }
                }
            }

            return (T)MemoryCache.Default[key];
        }

        /// <summary>
        /// 取缓存项,如果不存在则新增缓存项
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <param name="cachePopulate"></param>
        /// <param name="dependencyFilePath"></param>
        /// <returns></returns>
        public static T GetOrAddCacheItem<T>(String key, Func<T> cachePopulate, string dependencyFilePath)
        {
            if (String.IsNullOrWhiteSpace(key)) throw new ArgumentException("Invalid cache key");
            if (cachePopulate == null) throw new ArgumentNullException("cachePopulate");

            if (MemoryCache.Default[key] == null)
            {
                lock (_locker2)
                {
                    if (MemoryCache.Default[key] == null)
                    {
                        T cacheValue = cachePopulate();
                        if (!typeof(T).IsValueType && ((object)cacheValue) == null) //如果是引用类型且为NULL则不存缓存
                        {
                            return cacheValue;
                        }

                        var item = new CacheItem(key, cacheValue);
                        var policy = CreatePolicy(dependencyFilePath);

                        MemoryCache.Default.Add(item, policy);
                    }
                }
            }

            return (T)MemoryCache.Default[key];
        }

        /// <summary>
        /// 移除指定键的缓存项
        /// </summary>
        /// <param name="key"></param>
        public static void RemoveCacheItem(string key)
        {
            try
            {
                MemoryCache.Default.Remove(key);
            }
            catch
            { }
        }

        private static CacheItemPolicy CreatePolicy(TimeSpan? slidingExpiration, DateTime? absoluteExpiration)
        {
            var policy = new CacheItemPolicy();

            if (absoluteExpiration.HasValue)
            {
                policy.AbsoluteExpiration = absoluteExpiration.Value;
            }
            else if (slidingExpiration.HasValue)
            {
                policy.SlidingExpiration = slidingExpiration.Value;
            }

            policy.Priority = CacheItemPriority.Default;

            return policy;
        }

        private static CacheItemPolicy CreatePolicy(string filePath)
        {
            CacheItemPolicy policy = new CacheItemPolicy();
            policy.ChangeMonitors.Add(new HostFileChangeMonitor(new List<string>() { filePath }));
            policy.Priority = CacheItemPriority.Default;
            return policy;
        }
    }
}

支持：可指定绝对过期时间、滑动过期明间、文件依赖  三种缓存方式，目前已在公司各种生产业务项目中有使用。优点是可以根据数据的使用频率设置缓存有效期，特别是文件依赖缓存，比如：连接字符串读取一次后，若CONFIG文件没有改变，则缓存永久有效，一旦CONFIG更改，则缓存失效需重新读取，保证数据缓存的最大可用性，减少不必要的多次重复读取CONFIG。

使用示例很简单：(如下：会在第一次读取连接字符串并解密后返回给connstr变量，后续直接通过缓存KEY dbConnName直接返回连接字符串的结果，若修改了连接字符串的CONFIG文件，则缓存的项会失效，会重新读取连接字符串并重新加入到缓存中)
            string connstr= MemoryCacheUtil.GetOrAddCacheItem(dbConnName, () =>
            {
                var connStrSettings = ConfigUtil.GetConnectionString(dbConnName,dbConnectionStringConfigPath);
                string dbProdName = connStrSettings.ProviderName;
                string dbConnStr = connStrSettings.ConnectionString;
                return EncryptUtil.Decrypt(dbConnStr);
            }, "缓存依赖文件路路，如：c:appapp.config");