可灵活扩展的自定义session状态存储驱动

Session是互联网应用中非常重要的玩意儿，对于超过单台部署的站点集群，都会存在会话共享的需求。在web.config中，微软提供了sessionstate节点来定义不同的Session状态存储方式。本文就自定义模式下的Session状态存储驱动提供一些干货。

首先，想要接管Session状态存储，需要了解一些基本的东西。

SessionIDManager

/// <summary>    /// 自定义SessionID管理器    /// </summary>    public class CustomSessionIDManager : SessionIDManager    {        /// <summary>        /// 创建SessionID        /// </summary>        /// <param name="context"></param>        /// <returns></returns>        public override string CreateSessionID(HttpContext context)        {            return string.Format("{0}.{1}",  SessionPRoviderConfigurationSectionHandler.SessionProviderSettings.SessionProfix, base.CreateSessionID(context));        }        /// <summary>        /// 验证        /// </summary>        /// <param name="id"></param>        /// <returns></returns>        public override bool Validate(string id)        {            string prefix = string.Empty;            string realId = string.Empty;            if (string.IsNullOrEmpty(id) || id.Trim().Length == 0)            {                return false;            }            var parsedValues = id.Split('.');            if (parsedValues == null || parsedValues.Length != 2)            {                return false;            }            prefix = parsedValues[0];            realId = parsedValues[1];            return base.Validate(realId);        }    }

想要共享Session，肯定就会有SessionID的前缀需求，而SessionIDManager就提供了可自定义的虚方法，这边以CustomSessionIDManager举例。CreateSessionID方法提供了创建SessionID的实现，重载该方法，用{0}.{1}的方式提供基于前缀的SessionID生成。而Validate是拆解带前缀的SessionID来验证真实的SessionID。

SessionStateStoreProviderBase

/// <summary>    /// 自定义Session状态存储驱动    /// </summary>    public sealed class CustomSessionStateStoreProvider : SessionStateStoreProviderBase    {        /// <summary>        /// 构造函数        /// </summary>        public CustomSessionStateStoreProvider()        {            sessionStateStoreBehavior = SessionProviderBehaviorFactory.CreateSessionStateStoreBehaviorInstance();        }        /// <summary>        /// Session状态存储行为        /// </summary>        readonly ISessionStateStoreBehavior sessionStateStoreBehavior;        /// <summary>        /// 创建新的存储数据        /// </summary>        /// <param name="context"></param>        /// <param name="timeout"></param>        /// <returns></returns>        public override SessionStateStoreData CreateNewStoreData(System.Web.HttpContext context, int timeout)        {            return new SessionStateStoreData(new SessionStateItemCollection(), SessionStateUtility.GetSessionStaticObjects(context), timeout);        }        /// <summary>        /// 创建未初始化的项        /// </summary>        /// <param name="context"></param>        /// <param name="id"></param>        /// <param name="timeout"></param>        public override void CreateUninitializedItem(System.Web.HttpContext context, string id, int timeout)        {            sessionStateStoreBehavior.CreateUninitializedItem(context, id, timeout);        }        /// <summary>        /// 获取项        /// </summary>        /// <param name="context"></param>        /// <param name="id"></param>        /// <param name="locked"></param>        /// <param name="lockAge"></param>        /// <param name="lockId"></param>        /// <param name="actions"></param>        /// <returns></returns>        public override SessionStateStoreData GetItem(System.Web.HttpContext context, string id, out bool locked, out TimeSpan lockAge, out object lockId, out SessionStateActions actions)        {            return sessionStateStoreBehavior.GetItem(false, context, id, out locked, out lockAge, out lockId, out actions);        }        /// <summary>        /// 独占获取项        /// </summary>        /// <param name="context"></param>        /// <param name="id"></param>        /// <param name="locked"></param>        /// <param name="lockAge"></param>        /// <param name="lockId"></param>        /// <param name="actions"></param>        /// <returns></returns>        public override SessionStateStoreData GetItemExclusive(System.Web.HttpContext context, string id, out bool locked, out TimeSpan lockAge, out object lockId, out SessionStateActions actions)        {            return sessionStateStoreBehavior.GetItem(true, context, id, out locked, out lockAge, out lockId, out actions);        }        /// <summary>        /// 独占释放项        /// </summary>        /// <param name="context"></param>        /// <param name="id"></param>        /// <param name="lockId"></param>        public override void ReleaseItemExclusive(System.Web.HttpContext context, string id, object lockId)        {            sessionStateStoreBehavior.ReleaseItem(context, id, lockId);        }        /// <summary>        /// 移除项        /// </summary>        /// <param name="context"></param>        /// <param name="id"></param>        /// <param name="lockId"></param>        /// <param name="item"></param>        public override void RemoveItem(System.Web.HttpContext context, string id, object lockId, SessionStateStoreData item)        {            sessionStateStoreBehavior.RemoveItem(context, id, lockId);        }        /// <summary>        /// 重设项的超时时间        /// </summary>        /// <param name="context"></param>        /// <param name="id"></param>        public override void ResetItemTimeout(System.Web.HttpContext context, string id)        {            sessionStateStoreBehavior.ResetItemTimeout(context, id);        }        /// <summary>        /// 独占设置并释放项        /// </summary>        /// <param name="context"></param>        /// <param name="id"></param>        /// <param name="item"></param>        /// <param name="lockId"></param>        /// <param name="newItem"></param>        public override void SetAndReleaseItemExclusive(System.Web.HttpContext context, string id, SessionStateStoreData item, object lockId, bool newItem)        {            sessionStateStoreBehavior.SetAndReleaseItem(context, id, item, lockId, newItem);        }        /// <summary>        /// 回收        /// </summary>        public override void Dispose() { }        /// <summary>        /// 结束请求        /// </summary>        /// <param name="context"></param>        public override void EndRequest(System.Web.HttpContext context) { }        /// <summary>        /// 初始化请求        /// </summary>        /// <param name="context"></param>        public override void InitializeRequest(System.Web.HttpContext context) { }        /// <summary>        /// 设置项过期回掉        /// </summary>        /// <param name="expireCallback"></param>        /// <returns></returns>        public override bool SetItemExpireCallback(SessionStateItemExpireCallback expireCallback) { return false; }    }

SessionStateStoreProviderBase是提供Session状态存储驱动的基类。从基类分析，想要灵活扩展，核心就是对Session存储的那些方法实现进行抽象，让驱动在执行方法的时候不关心实现由谁来提供。因此，写一个SessionStateStoreBehavior接口，在CustomSessionStateStoreProvider的构造函数中，通过工厂在运行时得到实例。

SessionStateStoreBehavior

/// <summary>    /// Session状态存储行为接口    /// </summary>    public interface ISessionStateStoreBehavior    {        /// <summary>        /// 创建未初始化的项        /// </summary>        /// <param name="context"></param>        /// <param name="id"></param>        /// <param name="timeout"></param>        void CreateUninitializedItem(System.Web.HttpContext context, string id, int t