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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.” );
}
this.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：
this.dosomething( ccurrentsession.userid )
他的类其实也很简单，如下所示：
using system;
using system.web;
/**////——————————————————————–
/// developed by m. van eijkel – aug 2005
/// [e]: marcelvaneijkel@gmail.com
/// [w]: www.vaneijkel.com
namespace vaneijkel.web
{
/**//// <summary>
/// wrapper class for the session object.
/// it centralizes the logic for retrieving and validation of session information.
/// by using an approach like this you improve the protection and encapsulation of existing code.
/// it offers a simple, low-risk, easy manageable way to improve existing webapplication.
/// therfore, i call it webrefactoring.
/// </summary>
public class currentsession
{
constants#region constants
private const string smandatory_session_key_not_found_msg = “session variable excepted but does not exist. key={0}”;
private const string smandatory_session_value_invalid_null = “none null session value excepted. key={0}”;
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
/**//// <summary>
/// returns the userid as a int32 instead of an object.
/// this way you will get the compiler protection and intelligence support you need.
/// </summary>
public static int32 userid
{
get
{
return (int32) getvalueordefault( ekeys.userid, nuserid_unkown );
}
set
{
if ( nuserid_minimum >= value )
{
throw new applicationexception ( string.format(suserid_invalid, value, nuserid_minimum ));
}
setvalue( ekeys.userid, value );
}
}
#endregion
private: getvalueordefault( ekeys ekey, object odefaultvalue )#region private: getvalueordefault( ekeys ekey, object odefaultvalue )
/**//// <summary>
/// gets the value from the session object.
/// </summary>
/// <param name=”ekey”> the session key to get the value for.</param>
/// <param name=”odefaultvalue”>the default value to use if no valid value stored.</param>
/// <returns>when the value is null or the key does not exist,
/// the specified default value is returned.
/// otherwise, the value is returned</returns>
private static object getvalueordefault( ekeys ekey, object odefaultvalue )
{
//get the value
object ovalue = getvalue( ekey );
//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 )
/**//// <summary>
/// returns the session value for a session-key that must exist.
/// if the key does not exist an applicationexception is thrown.
/// </summary>
/// <param name=”ekey”> the session-key to return the session-value for. </param>
/// <returns> a none-null value.</returns>
private static object getmandatoryvalue( ekeys ekey )
{
//get the value
object ovalue = getvalue( ekey );
//key not found or value null?
if ( null == ovalue )
{
//throw applicationexception because its application logic error (none clr)
throw new applicationexception ( string.format( smandatory_session_key_not_found_msg, ekey.tostring() ));
}
//everything oke: return value
return ovalue;
}
#endregion
private: getvalue( ekeys ekey )#region private: getvalue( ekeys ekey )
/**//// <summary>
/// gets the session value from the specified key.
/// </summary>
/// <param name=”ekey”>the key to get the value from</param>
/// <returns>the session value for the specified session key.
/// if the key does not exist, null is returned.
/// </returns>
private static object getvalue( ekeys ekey )
{
return httpcontext.current.items[ ekey.tostring() ];
}
#endregion
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( string.format(smandatory_session_value_invalid_null, ekey.tostring() ) );
}
}
#endregion
private setvalue( ekeys ekey, object ovalue)#region private setvalue( ekeys ekey, object ovalue)
/**//// <summary>
/// stores the specified session-value to the specified session-key.
/// </summary>
/// <param name=”ekey”>the key for the value to store in the session.</param>
/// <param name=”ovalue”>the value to store in the session</param>
private static void setvalue ( ekeys ekey, object ovalue)
{
httpcontext.current.items[ekey.tostring()] = ovalue;
}
#endregion
/**//// <summary>
/// an enum for the
/// </summary>
private enum ekeys
{
userid
}
}
}
