C# MemoryCache学习笔记

    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");
        }
    }

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