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！

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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:\app\app.config");