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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." );
}
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]
namespace Va***jkel.Web
{
/**////
/// 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.
///
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
/**////
/// Returns the userID as a Int32 instead of an object.
/// This way you will get the compiler protection and intelligence support you need.
///
public static Int32 UserID
{
get
{
return (Int32) GetValueOrDefault( eK***.UserID, nUSERID_UNKOWN );
}
set
{
if ( nUSERID_MINIMUM >= value )
{
throw new ApplicationException ( St***g.Format(sUSERID_INVALID, value, nUSERID_MINIMUM ));
}
SetValue( eK***.UserID, value );
}
}
#endregion
private: GetValueOrDefault( eKeys eKey, Object oDefaultValue )#region private: GetValueOrDefault( eKeys eKey, Object oDefaultValue )
/**////
/// Gets the value from the session object.
///
/// The session key to get the value for.
/// The default value to use if no valid value stored.
///
/// the specified default value is returned.
/// Otherwise, the value is returned
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 )
/**////
/// Returns the session value for a session-key that must exist.
/// If the key does not exist an applicationException is thrown.
///
/// The session-key to return the session-value for.
///
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 ( 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 )
/**////
/// Gets the session value from the specified key.
///
/// The key to get the value from
///
/// If the key does not exist, null is returned.
///
private static object GetValue( eKeys eKey )
{
return Ht***ontext.Current.Items[ eK***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( St***g.Format(sMANDATORY_SESSION_VALUE_INVALID_NULL, eK***ToString() ) );
}
}
#endregion
private SetValue( eKeys eKey, Object oValue)#region private SetValue( eKeys eKey, Object oValue)
/**////
/// Stores the specified session-value to the specified session-key.
///
/// The key for the value to store in the session.
/// The value to store in the session
private static void SetValue ( eKeys eKey, Object oValue)
{
Ht***ontext.Current.Items[eK***ToString()] = oValue;
}
#endregion
/**////
/// An enum for the
///
private enum eKeys
{
UserID
}
}
}