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!

2018-02-11 15:00:28来源:cnblogs.com作者:梦在旅途人点击

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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");

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