.net core中基于MemoryCache封装的缓存类

环境：.net core2.2
nugt包依赖：
1. Microsoft.Extensions.Caching.Abstractions
2. Microsoft.Extensions.Caching.Memory

---

代码：
功能：根据时间过期的四种策略(1.永不过期、2.设置绝对过期时间点、3.设置过期滑动窗口、4.滑动窗口+过期绝对过期时间点)

using Microsoft.Extensions.Caching.Memory;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Reflection;

namespace server.Models
{
    public class CacheManager
    {

        public static CacheManager Default = new CacheManager();

        private IMemoryCache _cache = new MemoryCache(new MemoryCacheOptions());


        /// <summary>
        /// 判断是否在缓存中
        /// </summary>
        /// <param name="key">关键字</param>
        /// <returns></returns>
        public bool IsInCache(string key)
        {
            List<string> keys = GetAllKeys();
            foreach (var i in keys)
            {
                if (i == key) return true;
            }
            return false;
        }

        /// <summary>
        /// 获取所有缓存键
        /// </summary>
        /// <returns></returns>
        public List<string> GetAllKeys()
        {
            const BindingFlags flags = BindingFlags.Instance | BindingFlags.NonPublic;
            var entries = _cache.GetType().GetField("_entries", flags).GetValue(_cache);
            var cacheItems = entries as IDictionary;
            var keys = new List<string>();
            if (cacheItems == null) return keys;
            foreach (DictionaryEntry cacheItem in cacheItems)
            {
                keys.Add(cacheItem.Key.ToString());
            }
            return keys;
        }

        /// <summary>
        /// 获取所有的缓存值
        /// </summary>
        /// <returns></returns>
        public List<T> GetAllValues<T>()
        {
            var cacheKeys = GetAllKeys();
            List<T> vals = new List<T>();
            cacheKeys.ForEach(i =>
            {
                T t;
                if (_cache.TryGetValue<T>(i, out t))
                {
                    vals.Add(t);
                }
            });
            return vals;
        }
        /// <summary>
        /// 取得缓存数据
        /// </summary>
        /// <typeparam name="T">类型值</typeparam>
        /// <param name="key">关键字</param>
        /// <returns></returns>
        public T Get<T>(string key)
        {
            if (string.IsNullOrWhiteSpace(key))
                throw new ArgumentNullException(nameof(key));
            T value;
            _cache.TryGetValue<T>(key, out value);
            return value;
        }

        /// <summary>
        /// 设置缓存(永不过期)
        /// </summary>
        /// <param name="key">关键字</param>
        /// <param name="value">缓存值</param>
        public void Set_NotExpire<T>(string key, T value)
        {
            if (string.IsNullOrWhiteSpace(key))
                throw new ArgumentNullException(nameof(key));

            T v;
            if (_cache.TryGetValue(key, out v))
                _cache.Remove(key);
            _cache.Set(key, value);
        }

        /// <summary>
        /// 设置缓存(滑动过期:超过一段时间不访问就会过期,一直访问就一直不过期)
        /// </summary>
        /// <param name="key">关键字</param>
        /// <param name="value">缓存值</param>
        public void Set_SlidingExpire<T>(string key, T value, TimeSpan span)
        {
            if (string.IsNullOrWhiteSpace(key))
                throw new ArgumentNullException(nameof(key));

            T v;
            if (_cache.TryGetValue(key, out v))
                _cache.Remove(key);
            _cache.Set(key, value, new MemoryCacheEntryOptions()
            {
                SlidingExpiration = span
            });
        }

        /// <summary>
        /// 设置缓存(绝对时间过期:从缓存开始持续指定的时间段后就过期,无论有没有持续的访问)
        /// </summary>
        /// <param name="key">关键字</param>
        /// <param name="value">缓存值</param>
        public void Set_AbsoluteExpire<T>(string key, T value, TimeSpan span)
        {
            if (string.IsNullOrWhiteSpace(key))
                throw new ArgumentNullException(nameof(key));

            T v;
            if (_cache.TryGetValue(key, out v))
                _cache.Remove(key);
            _cache.Set(key, value, span);
        }

        /// <summary>
        /// 设置缓存(绝对时间过期+滑动过期:比如滑动过期设置半小时,绝对过期时间设置2个小时，那么缓存开始后只要半小时内没有访问就会立马过期,如果半小时内有访问就会向后顺延半小时，但最多只能缓存2个小时)
        /// </summary>
        /// <param name="key">关键字</param>
        /// <param name="value">缓存值</param>
        public void Set_SlidingAndAbsoluteExpire<T>(string key, T value, TimeSpan slidingSpan, TimeSpan absoluteSpan)
        {
            if (string.IsNullOrWhiteSpace(key))
                throw new ArgumentNullException(nameof(key));

            T v;
            if (_cache.TryGetValue(key, out v))
                _cache.Remove(key);
            _cache.Set(key, value, new MemoryCacheEntryOptions()
            {
                SlidingExpiration = slidingSpan,
                AbsoluteExpiration = DateTimeOffset.Now.AddMilliseconds(absoluteSpan.Milliseconds)
            });
        }

        /// <summary>
        /// 移除缓存
        /// </summary>
        /// <param name="key">关键字</param>
        public void Remove(string key)
        {
            if (string.IsNullOrWhiteSpace(key))
                throw new ArgumentNullException(nameof(key));

            _cache.Remove(key);
        }

        /// <summary>
        /// 释放
        /// </summary>
        public void Dispose()
        {
            if (_cache != null)
                _cache.Dispose();
            GC.SuppressFinalize(this);
        }
    }
}

最后附上四种过期策略的实验代码：

using Microsoft.Extensions.Caching.Memory;
using System;
using System.Threading.Tasks;

namespace ConsoleApp6
{
    class Program
    {
        public static IMemoryCache _cache = new MemoryCache(new MemoryCacheOptions());
        static async Task Main(string[] args)
        {
            //await Test1();
            //await Test2();
            //await Test3();
            await Test4();
            Console.WriteLine("ok");
            Console.ReadLine();
        }

        /// <summary>
        /// 4.验证滑动窗口+绝对过期时间(这里的绝对过期时间是缓存从开始到结束最长的时间,滑动窗口表示在滑动时间内只要没访问就立马过期)
        /// </summary>
        /// <returns></returns>
        private async static Task Test4()
        {
            _cache.Set("xiaoming", "222", new MemoryCacheEntryOptions()
            {
                SlidingExpiration = TimeSpan.FromSeconds(1.5),
                AbsoluteExpiration = DateTimeOffset.Now.AddMilliseconds(1000 * 3.5)
            });
            await Task.Delay(1000 * 1);
            Console.WriteLine("1s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("2s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("3s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("4s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("5s:" + _cache.Get("xiaoming"));
        }

        /// <summary>
        /// 3.验证滑动窗口过期
        /// </summary>
        /// <returns></returns>
        private async static Task Test3()
        {
            _cache.Set("xiaoming", "222", new MemoryCacheEntryOptions()
            {
                SlidingExpiration = TimeSpan.FromSeconds(1.5)
            });
            await Task.Delay(1000 * 1);
            Console.WriteLine("1s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("2s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("3s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("4s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("5s:" + _cache.Get("xiaoming"));
        }

        /// <summary>
        /// 2.验证绝对过期时间
        /// </summary>
        /// <returns></returns>
        private async static Task Test2()
        {
            _cache.Set("xiaoming", "222", TimeSpan.FromSeconds(3));
            await Task.Delay(1000 * 1);
            Console.WriteLine("1s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("2s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("3s:" + _cache.Get("xiaoming"));
            await Task.Delay(1000 * 1);
            Console.WriteLine("4s:" + _cache.Get("xiaoming"));
        }

        /// <summary>
        /// 1.验证永不过期
        /// </summary>
        private async static Task Test1()
        {
            _cache.Set("xiaoming", "222");
            await Task.Delay(1000 * 3);
            Console.WriteLine(_cache.Get("xiaoming"));
        }
    }
}