memoryCache的使用

1 借鉴这篇文章

https://www.cnblogs.com/zuowj/p/8440902.html

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

namespace ConsoleApp1
{
    public static class MemoryCacheHelper
    {
        private static readonly object _locker = new object();
        private static readonly object _locker2 = new object();

        /// <summary>
        /// 根据key取缓存，不存在则返回null
        /// </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 (Exception ex)
            {

                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);
        }

        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 ArgumentException("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)
                        {
                            return cacheValue;
                        }
                        var item = new CacheItem(key, cacheValue);
                        var policy = CreatePolicy(slidingExpiration, absoluteExpiration);
                        MemoryCache.Default.Add(item, policy);
                    }

                }
            }

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

        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 ArgumentException("cachePopulate");
            }

            if (MemoryCache.Default[key]==null)
            {
                lock (_locker2)
                {
                    if (MemoryCache.Default[key] == null)
                    {
                        T cacheValue = cachePopulate();
                        if (!typeof(T).IsValueType && ((object)cacheValue) == null)
                        {
                            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 (Exception)
            {

            }
        }

        private static CacheItemPolicy CreatePolicy(TimeSpan? slidingExpiration, DateTime? absoluteExpiration)
        {
            var policy = new CacheItemPolicy();
            if (slidingExpiration.HasValue)
            {
                policy.SlidingExpiration = slidingExpiration.Value;
            }
            else if (absoluteExpiration.HasValue)
            {
                policy.AbsoluteExpiration = absoluteExpiration.Value;
            }

            policy.Priority = CacheItemPriority.Default;
            return policy;
        }

        /// <summary>
        /// 缓存文件
        /// </summary>
        /// <param name="filepath"></param>
        /// <returns></returns>
        private static CacheItemPolicy CreatePolicy(string filepath)
        {
            var policy = new CacheItemPolicy();
            policy.ChangeMonitors.Add(new HostFileChangeMonitor(new List<string>() { filepath }));

            policy.Priority = CacheItemPriority.Default;
            return policy;
        }
    }
}