C# MemoryCache学习笔记
原文网址：https://www.cnblogs.com/atomy/archive/2020/02/27/12372678.html
很多情况下需要用到缓存，合理利用缓存一方面可以提高程序的响应速度，同时可以减少对特定资源访问的压力。为了避免每次请求都去访问后台的资源（例如数据库），一般会考虑将一些更新不是很频繁的、可以重用的数据，通过一定的方式临时地保存起来，后续的请求根据情况可以直接访问这些保存起来的数据，这种机制就是所谓的缓存机制。
.NET 4.0的缓存功能主要由三部分组成：System.Runtime.Caching，System.Web.Caching.Cache和Output Cache。
MemoryCache：这个是在.NET 4.0中新增的缓存框架，Namespace:System.Runtime.Caching ，Assembly:System.Runtime.Caching.dll。
System.Web.Caching.Cache：这个是在.NET 2.0开始就一直存在的缓存对象，一般主要用在Web中，当然也可以用于Winform里面，不过要引用System.Web.dll。
Output Cache：这个是在Asp.NET里面使用的。在ASP.NET 4.0之前，都是直接使用System.Web.Caching.Cache来缓存HTML片段。在ASP.NET 4.0中对它进行了重新设计，提供了一个OutputCacheProvider供开发人员进行扩展，但是它默认情况下，仍然使用System.Web.Caching.Cache来做做缓存。
下面演示MemoryCache的简单使用：
1、添加一个类，命名为ConfigHelper，代码如下：
/// <summary>
/// 配置帮助类
/// </summary>
class ConfigHelper
{
/// <summary>
/// 获取管理配置文件对象
/// </summary>
/// <param name="configPath">指定要管理的配置文件路径，如果为空或不存在，则为管理程序集默认的配置文件路径。</param>
/// <returns></returns>
private static Configuration GetConfiguration(string configPath = null)
{
if (!string.IsNullOrEmpty(configPath) && File.Exists(configPath))
{
ExeConfigurationFileMap map = new ExeConfigurationFileMap
{
ExeConfigFilename = configPath
};
return ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);
}
else
{
return ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
}
}
/// <summary>
/// 获取指定配置文件+配置名称的配置项的值
/// </summary>
public static string GetAppSettingValue(string key, string defaultValue = null, string configPath = null)
{
var config = GetConfiguration(configPath);
var appSetting = config.AppSettings.Settings[key];
return appSetting.Value;
}
/// <summary>
/// 获取所有配置值
/// </summary>
public static Dictionary<string, string> GetAppSettingValues(string configPath = null)
{
Dictionary<string, string> settingDic = new Dictionary<string, string>();
var config = GetConfiguration(configPath);
var settings = config.AppSettings.Settings;
foreach (string key in settings.AllKeys)
{
settingDic[key] = settings[key].ToString();
}
return settingDic;
}
/// <summary>
/// 设置配置值（存在则更新，不存在则新增。）
/// </summary>
public static void SetAppSettingValue(string key, string value, string configPath = null)
{
var config = GetConfiguration(configPath);
var setting = config.AppSettings.Settings[key];
if (setting == null)
{
config.AppSettings.Settings.Add(key, value);
}
else
{
setting.Value = value;
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");
}
/// <summary>
/// 设置多个配置值（存在则更新，不存在则新增）
/// </summary>
public static void SetAppSettingValues(IEnumerable<KeyValuePair<string, string>> settingValues, string configPath = null)
{
var config = GetConfiguration(configPath);
foreach (var item in settingValues)
{
var setting = config.AppSettings.Settings[item.Key];
if (setting == null)
{
config.AppSettings.Settings.Add(item.Key, item.Value);
}
else
{
setting.Value = item.Value;
}
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");
}
/// <summary>
/// 删除配置值
/// </summary>
public static void RemoveAppSetting(string key, string configPath = null)
{
var config = GetConfiguration(configPath);
config.AppSettings.Settings.Remove(key);
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");
}
/// <summary>
/// 删除多个配置值
/// </summary>
public static void RemoveAppSettings(string configPath = null, params string[] keys)
{
var config = GetConfiguration(configPath);
if (keys != null)
{
foreach (string key in keys)
{
config.AppSettings.Settings.Remove(key);
}
}
else
{
config.AppSettings.Settings.Clear();
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");
}
/// <summary>
/// 获取连接字符串
/// </summary>
public static string GetConnectionString(string name, string defaultconnString = null, string configPath = null)
{
var config = GetConfiguration(configPath);
var connStringSettings = config.ConnectionStrings.ConnectionStrings[name];
if (connStringSettings == null)
{
return defaultconnString;
}
return connStringSettings.ConnectionString;
}
/// <summary>
/// 获取指定配置文件+连接名称的连接字符串配置项
/// </summary>
public static ConnectionStringSettings GetConnectionStringSetting(string name, string configPath = null)
{
var config = GetConfiguration(configPath);
var connStringSettings = config.ConnectionStrings.ConnectionStrings[name];
return connStringSettings;
}
/// <summary>
/// 获取所有的连接字符串配置项
/// </summary>
public static Dictionary<string, ConnectionStringSettings> GetConnectionStringSettings(string configPath = null)
{
var config = GetConfiguration(configPath);
var connStringSettingDic = new Dictionary<string, ConnectionStringSettings>();
var connStringSettings = ConfigurationManager.ConnectionStrings;
foreach (ConnectionStringSettings item in connStringSettings)
{
connStringSettingDic[item.Name] = item;
}
return connStringSettingDic;
}
/// <summary>
/// 设置连接字符串的值（存在则更新，不存在则新增。）
/// </summary>
public static void SetConnectionString(string name, string connString, string provider, string configPath = null)
{
var config = GetConfiguration(configPath);
ConnectionStringSettings connStringSettings = config.ConnectionStrings.ConnectionStrings[name];
if (connStringSettings != null)
{
connStringSettings.ConnectionString = connString;
connStringSettings.ProviderName = provider;
}
else
{
connStringSettings = new ConnectionStringSettings(name, connString, provider);
config.ConnectionStrings.ConnectionStrings.Add(connStringSettings);
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("connectionStrings");
}
/// <summary>
/// 设置多个连接字符串的值（存在则更新，不存在则新增。）
/// </summary>
public static void SetConnectionStrings(IEnumerable<ConnectionStringSettings> connStringSettings, string configPath = null)
{
var config = GetConfiguration(configPath);
foreach (var item in connStringSettings)
{
ConnectionStringSettings connStringSetting = config.ConnectionStrings.ConnectionStrings[item.Name];
if (connStringSetting != null)
{
connStringSetting.ConnectionString = item.ConnectionString;
connStringSetting.ProviderName = item.ProviderName;
}
else
{
config.ConnectionStrings.ConnectionStrings.Add(item);
}
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("connectionStrings");
}
/// <summary>
/// 删除连接字符串配置项
/// </summary>
public static void RemoveConnectionString(string name, string configPath = null)
{
var config = GetConfiguration(configPath);
config.ConnectionStrings.ConnectionStrings.Remove(name);
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("connectionStrings");
}
/// <summary>
/// 删除多个连接字符串配置项
/// </summary>
public static void RemoveConnectionStrings(string configPath = null, params string[] names)
{
var config = GetConfiguration(configPath);
if (names != null)
{
foreach (string name in names)
{
config.ConnectionStrings.ConnectionStrings.Remove(name);
}
}
else
{
config.ConnectionStrings.ConnectionStrings.Clear();
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("connectionStrings");
}
}
/// <summary>
/// 配置帮助类
/// </summary>
class ConfigHelper
{
/// <summary>
/// 获取管理配置文件对象
/// </summary>
/// <param name="configPath">指定要管理的配置文件路径，如果为空或不存在，则为管理程序集默认的配置文件路径。</param>
/// <returns></returns>
private static Configuration GetConfiguration(string configPath = null)
{
if (!string.IsNullOrEmpty(configPath) && File.Exists(configPath))
{
ExeConfigurationFileMap map = new ExeConfigurationFileMap
{
ExeConfigFilename = configPath
};
return ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);
}
else
{
return ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
}
}
/// <summary>
/// 获取指定配置文件+配置名称的配置项的值
/// </summary>
public static string GetAppSettingValue(string key, string defaultValue = null, string configPath = null)
{
var config = GetConfiguration(configPath);
var appSetting = config.AppSettings.Settings[key];
return appSetting.Value;
}
/// <summary>
/// 获取所有配置值
/// </summary>
public static Dictionary<string, string> GetAppSettingValues(string configPath = null)
{
Dictionary<string, string> settingDic = new Dictionary<string, string>();
var config = GetConfiguration(configPath);
var settings = config.AppSettings.Settings;
foreach (string key in settings.AllKeys)
{
settingDic[key] = settings[key].ToString();
}
return settingDic;
}
/// <summary>
/// 设置配置值（存在则更新，不存在则新增。）
/// </summary>
public static void SetAppSettingValue(string key, string value, string configPath = null)
{
var config = GetConfiguration(configPath);
var setting = config.AppSettings.Settings[key];
if (setting == null)
{
config.AppSettings.Settings.Add(key, value);
}
else
{
setting.Value = value;
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");
}
/// <summary>
/// 设置多个配置值（存在则更新，不存在则新增）
/// </summary>
public static void SetAppSettingValues(IEnumerable<KeyValuePair<string, string>> settingValues, string configPath = null)
{
var config = GetConfiguration(configPath);
foreach (var item in settingValues)
{
var setting = config.AppSettings.Settings[item.Key];
if (setting == null)
{
config.AppSettings.Settings.Add(item.Key, item.Value);
}
else
{
setting.Value = item.Value;
}
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");
}
/// <summary>
/// 删除配置值
/// </summary>
public static void RemoveAppSetting(string key, string configPath = null)
{
var config = GetConfiguration(configPath);
config.AppSettings.Settings.Remove(key);
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");
}
/// <summary>
/// 删除多个配置值
/// </summary>
public static void RemoveAppSettings(string configPath = null, params string[] keys)
{
var config = GetConfiguration(configPath);
if (keys != null)
{
foreach (string key in keys)
{
config.AppSettings.Settings.Remove(key);
}
}
else
{
config.AppSettings.Settings.Clear();
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("appSettings");
}
/// <summary>
/// 获取连接字符串
/// </summary>
public static string GetConnectionString(string name, string defaultconnString = null, string configPath = null)
{
var config = GetConfiguration(configPath);
var connStringSettings = config.ConnectionStrings.ConnectionStrings[name];
if (connStringSettings == null)
{
return defaultconnString;
}
return connStringSettings.ConnectionString;
}
/// <summary>
/// 获取指定配置文件+连接名称的连接字符串配置项
/// </summary>
public static ConnectionStringSettings GetConnectionStringSetting(string name, string configPath = null)
{
var config = GetConfiguration(configPath);
var connStringSettings = config.ConnectionStrings.ConnectionStrings[name];
return connStringSettings;
}
/// <summary>
/// 获取所有的连接字符串配置项
/// </summary>
public static Dictionary<string, ConnectionStringSettings> GetConnectionStringSettings(string configPath = null)
{
var config = GetConfiguration(configPath);
var connStringSettingDic = new Dictionary<string, ConnectionStringSettings>();
var connStringSettings = ConfigurationManager.ConnectionStrings;
foreach (ConnectionStringSettings item in connStringSettings)
{
connStringSettingDic[item.Name] = item;
}
return connStringSettingDic;
}
/// <summary>
/// 设置连接字符串的值（存在则更新，不存在则新增。）
/// </summary>
public static void SetConnectionString(string name, string connString, string provider, string configPath = null)
{
var config = GetConfiguration(configPath);
ConnectionStringSettings connStringSettings = config.ConnectionStrings.ConnectionStrings[name];
if (connStringSettings != null)
{
connStringSettings.ConnectionString = connString;
connStringSettings.ProviderName = provider;
}
else
{
connStringSettings = new ConnectionStringSettings(name, connString, provider);
config.ConnectionStrings.ConnectionStrings.Add(connStringSettings);
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("connectionStrings");
}
/// <summary>
/// 设置多个连接字符串的值（存在则更新，不存在则新增。）
/// </summary>
public static void SetConnectionStrings(IEnumerable<ConnectionStringSettings> connStringSettings, string configPath = null)
{
var config = GetConfiguration(configPath);
foreach (var item in connStringSettings)
{
ConnectionStringSettings connStringSetting = config.ConnectionStrings.ConnectionStrings[item.Name];
if (connStringSetting != null)
{
connStringSetting.ConnectionString = item.ConnectionString;
connStringSetting.ProviderName = item.ProviderName;
}
else
{
config.ConnectionStrings.ConnectionStrings.Add(item);
}
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("connectionStrings");
}
/// <summary>
/// 删除连接字符串配置项
/// </summary>
public static void RemoveConnectionString(string name, string configPath = null)
{
var config = GetConfiguration(configPath);
config.ConnectionStrings.ConnectionStrings.Remove(name);
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("connectionStrings");
}
/// <summary>
/// 删除多个连接字符串配置项
/// </summary>
public static void RemoveConnectionStrings(string configPath = null, params string[] names)
{
var config = GetConfiguration(configPath);
if (names != null)
{
foreach (string name in names)
{
config.ConnectionStrings.ConnectionStrings.Remove(name);
}
}
else
{
config.ConnectionStrings.ConnectionStrings.Clear();
}
config.Save(ConfigurationSaveMode.Modified);
ConfigurationManager.RefreshSection("connectionStrings");
}
}
2、添加一个类，命名为MemoryCacheHelper（注意需引用System.Runtime.Caching.dll），代码如下：
/// <summary>
/// 内存缓存帮助类，支持绝对过期时间、滑动过期时间、文件依赖三种缓存方式。
/// </summary>
class MemoryCacheHelper
{
private static readonly object _locker1 = 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 (_locker1)
{
if (MemoryCache.Default[key] == null)
{
T cacheValue = cachePopulate();
if (!typeof(T).IsValueType && 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 && 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>
/// 指定缓存项的一组逐出和过期详细信息
/// </summary>
/// <param name="slidingExpiration"></param>
/// <param name="absoluteExpiration"></param>
/// <returns></returns>
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;
}
/// <summary>
/// 指定缓存项的一组逐出和过期详细信息
/// </summary>
/// <param name="filePath"></param>
/// <returns></returns>
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;
}
/// <summary>
/// 移除指定键的缓存项
/// </summary>
/// <param name="key"></param>
public static void RemoveCacheItem(string key)
{
if (Contains(key))
{
MemoryCache.Default.Remove(key);
}
}
}
3、添加一个WinForm窗体，命名为Main，并添加一个按钮。
4、配置App.config：
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
</startup>
<connectionStrings>
<add name ="connString" connectionString="server=.;database=db_test;uid=sa;pwd=********;" />
</connectionStrings>
</configuration>
5、Main窗体代码如下：
private void button1_Click(object sender, EventArgs e)
{
int times1 = 0, times2 = 0;
for (int i = 0; i < 10; i++)
{
if (MemoryCacheHelper.Contains("connString"))
{
times1++;
}
else
{
times2++;
string connstr = MemoryCacheHelper.GetOrAddCacheItem("connString", () =>
{
return ConfigHelper.GetConnectionString("connString", null);
}, Application.StartupPath + @"\App.config");
}
}
MessageBox.Show($"内存缓存读取次数：{times1}，非内存缓存读取次数：{times2}", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
}
6、运行结果如下：
浙公网安备 33010602011771号