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!

2021-02-15 03:19

阅读:609

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

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

        /// 
        /// 取缓存项,如果不存在则返回空
        /// 
        /// 
        /// 
        /// 
        public static T GetCacheItem(String key)
        {
            try
            {
                return (T)MemoryCache.Default[key];
            }
            catch
            {
                return default(T);
            }
        }

        /// 
        /// 是否包含指定键的缓存项
        /// 
        /// 
        /// 
        public static bool Contains(string key)
        {
            return MemoryCache.Default.Contains(key);
        }

        /// 
        /// 取缓存项,如果不存在则新增缓存项
        /// 
        /// 
        /// 
        /// 
        /// 
        /// 
        /// 
        public static T GetOrAddCacheItem(String key, Func 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];
        }

        /// 
        /// 取缓存项,如果不存在则新增缓存项
        /// 
        /// 
        /// 
        /// 
        /// 
        /// 
        public static T GetOrAddCacheItem(String key, Func 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];
        }

        /// 
        /// 移除指定键的缓存项
        /// 
        /// 
        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() { 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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