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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");
本文转自 梦在旅途 博客园博客，原文链接：http://www.cnblogs.com/zuowj/p/8440902.html ，如需转载请自行联系原作者