在HttpModule中使用 System.Thread.Timer
可以在一定程度上实现 定时任务/后台任务
只是在 Timer的TimerCallback的代理方法，将在一个新线程中运行
若在方法中/或者该方法调用的一些方法中， 调用了 System.Web.HttpContext.Current 都将返回null
***
如现在给上海贝尔作的一个eKap项目中，是用IBatisNet组件， 该组件中
namespace IBatisNet.DataMapper.SessionContainer
{
/// <summary>
/// Build a session container for a Windows or Web context.
/// </summary>
public class SessionContainerFactory
{
#region Methods
/// <summary>
/// Get a session container for a Windows or Web context.
/// </summary>
/// <returns></returns>
static public ISessionContainer GetSessionContainer()
{
if (System.Web.HttpContext.Current == null)
{
return new WindowSessionContainer();
}
else
{
return new WebSessionContainer();
}
}
#endregion
}
}
其中 WebSessionContainer 类:
/// <summary>
/// Session container for web application.
/// </summary>
public class WebSessionContainer : ISessionContainer
{
#region Constants
/// <summary>
/// Token for SqlMapConfig xml root.
/// </summary>
private const string LOCAL_SESSION = "_IBATIS_LOCAL_SQLMAPSESSION_";
#endregion
#region Constructor (s) / Destructor
/// <summary>
/// Constructor
/// </summary>
public WebSessionContainer()
{
System.Web.HttpContext.Current.Items[LOCAL_SESSION] = null;
}
#endregion
#region ISessionContainer Members
#region Properties
/// <summary>
/// Get the local session
/// </summary>
public SqlMapSession LocalSession
{
get
{
// add by sharper
if(System.Web.HttpContext.Current != null)
{
return System.Web.HttpContext.Current.Items[LOCAL_SESSION] as SqlMapSession;
}else
{
return null;
}
}
}
#endregion
#region Methods
/// <summary>
/// Store the local session on the container.
/// Ensure that the session is unique for each thread.
/// </summary>
/// <param name="session">The session to store</param>
public void Store(SqlMapSession session)
{
System.Web.HttpContext.Current.Items[LOCAL_SESSION] = session;
}
/// <summary>
/// Remove the local session from the container.
/// </summary>
public void Dispose()
{
System.Web.HttpContext.Current.Items[LOCAL_SESSION] = null;
}
#endregion
#endregion
}
其中原先 LocalSession 属性没有判断
System.Web.HttpContext.Current 是否为null
所以会引发一个 NullReferenceException
