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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
