[ASP.NET]重构Session确实让代码简洁干净了不少

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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 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：

usingSystem;
usingSystem.Web;

/**////--------------------------------------------------------------------
///DevelopedbyM.vanEijkel-aug2005
///[e]:[e-mail]
///[w]:www.vaneijkel.com

namespaceVanEijkel.Web
{
/**////<summary></summary>
///Wrapperclassforthesessionobject.
///Itcentralizesthelogicforretrievingandvalidationofsessioninformation.
///Byusinganapproachlikethisyouimprovetheprotectionandencapsulationofexistingcode.
///Itoffersasimple,low-risk,easymanageablewaytoimproveexistingWebApplication.
///Therfore,IcallitwebRefactoring.
///
publicclassCurrentSession
{
Constants#regionConstants
privateconstStringsMANDATORY_SESSION_KEY_NOT_FOUND_MSG="Sessionvariableexceptedbutdoesnotexist.Key={0}";
privateconstStringsMANDATORY_SESSION_VALUE_INVALID_NULL="Nonenullsessionvalueexcepted.Key={0}";

privateconstInt32nUSERID_UNKOWN=-1;
privateconstInt32nUSERID_MINIMUM=1;
privateconstStringsUSERID_INVALID="InvalidUserID:{0}.UserIDshouldbelargerthan:{1}";
#endregion

UserID#regionUserID
/**////<summary></summary>
///ReturnstheuserIDasaInt32insteadofanobject.
///Thiswayyouwillgetthecompilerprotectionandintelligencesupportyouneed.
///
publicstaticInt32UserID
{
get
{
return(Int32)GetValueOrDefault(eKeys.UserID,nUSERID_UNKOWN);
}
set
{
if(nUSERID_MINIMUM>=value)
{
thrownewApplicationException(String.Format(sUSERID_INVALID,value,nUSERID_MINIMUM));
}
SetValue(eKeys.UserID,value);
}
}
#endregion

private:GetValueOrDefault(eKeyseKey,ObjectoDefaultValue)#regionprivate:GetValueOrDefault(eKeyseKey,ObjectoDefaultValue)
/**////<summary></summary>
///Getsthevaluefromthesessionobject.
///
///Thesessionkeytogetthevaluefor.
///Thedefaultvaluetouseifnovalidvaluestored.
///<returns></returns>Whenthevalueisnullorthekeydoesnotexist,
///thespecifieddefaultvalueisreturned.
///Otherwise,thevalueisreturned
privatestaticobjectGetValueOrDefault(eKeyseKey,ObjectoDefaultValue)
{
//getthevalue
objectoValue=GetValue(eKey);

//valuenotfoundornull?
if(null==oValue)
{
//returndefaultvalue
returnoDefaultValue;
}

//everythingoke:returnsessionvalue
returnoValue;
}
#endregion
private:GetMandatoryValue(eKeyseKey)#regionprivate:GetMandatoryValue(eKeyseKey)
/**////<summary></summary>
///Returnsthesessionvalueforasession-keythatmustexist.
///IfthekeydoesnotexistanapplicationExceptionisthrown.
///
///Thesession-keytoreturnthesession-valuefor.
///<returns></returns>Anone-nullvalue.
privatestaticobjectGetMandatoryValue(eKeyseKey)
{
//getthevalue
objectoValue=GetValue(eKey);

//keynotfoundorvaluenull?
if(null==oValue)
{
//throwapplicationExceptionbecauseitsapplicationlogicerror(noneCLR)
thrownewApplicationException(String.Format(sMANDATORY_SESSION_KEY_NOT_FOUND_MSG,eKey.ToString()));
}

//everythingoke:returnvalue
returnoValue;
}
#endregion
private:GetValue(eKeyseKey)#regionprivate:GetValue(eKeyseKey)
/**////<summary></summary>
///Getsthesessionvaluefromthespecifiedkey.
///
///Thekeytogetthevaluefrom
///<returns></returns>Thesessionvalueforthespecifiedsessionkey.
///Ifthekeydoesnotexist,nullisreturned.
///
privatestaticobjectGetValue(eKeyseKey)
{
returnHttpContext.Current.Items[eKey.ToString()];
}
#endregion

privateSetMandatoryValue(eKeyseKey,ObjectoValue)#regionprivateSetMandatoryValue(eKeyseKey,ObjectoValue)
privatestaticvoidSetMandatoryValue(eKeyseKey,ObjectoValue)
{
if(null==oValue)
{
thrownewApplicationException(String.Format(sMANDATORY_SESSION_VALUE_INVALID_NULL,eKey.ToString()));
}
}
#endregion
privateSetValue(eKeyseKey,ObjectoValue)#regionprivateSetValue(eKeyseKey,ObjectoValue)
/**////<summary></summary>
///Storesthespecifiedsession-valuetothespecifiedsession-key.
///
///Thekeyforthevaluetostoreinthesession.
///Thevaluetostoreinthesession
privatestaticvoidSetValue(eKeyseKey,ObjectoValue)
{
HttpContext.Current.Items[eKey.ToString()]=oValue;
}
#endregion

/**////<summary></summary>
///Anenumforthe
///
privateenumeKeys
{
UserID
}
}
}