重构Session确实让代码简洁干净了不少

CodeProject的这篇文章确实对我有所启迪，
http://www.codeproject.com/useritems/SessionWrapper.asp#xx1208856xx。

诚如作者所说，我们经常在ASP.NET用许多类似于下面的代码来检测Session中存储的对象，来防止Session过期后存储的变量丢失问题：
Int32 nUserID = -1;
if ( null != Session["userID"] ) {
  if ( Session["userID"] is Int32 ) {
    if ( 0 < Session["userID"] ) {
      nUserID = (Int32) Session["userID"]
    }
  }
}
if ( -1 == nUserID )
{
  throw new ApplicationException ( "Unexpected situation: userID invalid." );
}

th***doSomething( nUserID );
这样的代码会遍布各处。

那么，利用他的这个封装方案来做重构，确实让代码简洁干净了不少！
经过他的封装，上面的代码用这么一句话就行了：

th***doSomething( CC***entSession.UserID )

他的类其实也很简单，如下所示：

using System;
using Sy***m.Web;

/**////--------------------------------------------------------------------
/// Developed by M. van Eijkel - aug 2005
/// [e]: ma***[email protected]">ma***[email protected]
/// [w]: ww***aneijkel.com">ww***aneijkel.com

namespace Va***jkel.Web
{
    /**////

    private const Int32 nUSERID_UNKOWN = -1;
    private const Int32 nUSERID_MINIMUM = 1;
    private const String sUSERID_INVALID = "Invalid UserID:{0}. UserID should be larger than:{1}";
    #endregion

    UserID#region UserID
    /**////

    private: GetValueOrDefault( eKeys eKey, Object oDefaultValue )#region private: GetValueOrDefault( eKeys eKey, Object oDefaultValue )
    /**////

      //value not found or null?
      if (null == oValue)
      {
        //return default value
        return oDefaultValue;
      }

      //everything oke: return session value
      return oValue;
    }
    #endregion
    private: GetMandatoryValue( eKeys eKey )#region private: GetMandatoryValue( eKeys eKey )
    /**////

      //key not found or value null?
      if ( null == oValue )
      {
        //throw applicationException because its application logic error (none CLR)
        throw new ApplicationException ( St***g.Format( sMANDATORY_SESSION_KEY_NOT_FOUND_MSG, eK***ToString() ));
      }

      //everything oke: return value
      return oValue;
    }
    #endregion
    private: GetValue( eKeys eKey )#region private: GetValue( eKeys eKey )
    /**////

    private SetMandatoryValue( eKeys eKey, Object oValue )#region private SetMandatoryValue( eKeys eKey, Object oValue )
    private static void SetMandatoryValue( eKeys eKey, Object oValue )
    {
      if ( null == oValue )
      {
        throw new ApplicationException(  St***g.Format(sMANDATORY_SESSION_VALUE_INVALID_NULL, eK***ToString() ) );
      }
    }
    #endregion
    private SetValue( eKeys eKey, Object oValue)#region private SetValue( eKeys eKey, Object oValue)
    /**////

    /**////