程序健壮性最基本要求就是程序错误的处理与捕捉，在ASP.NET中，错误的处理有和其他编程语言一样的机制，可以使用Try…Catch…Finally等方式，这一点和ASP相比具有较大的进步。而且，使用这些错误处理方法，可以大大提高程序的可读性和程序调试速度，在这几个优势结合的情况下，我们更加应该注意这一点。

关于错误的处理，我们可以参考这篇文章:

Try...Catch...FinallyinASP.NET

Introduction

ErrorhandlinginClassicASPwasnotthebest.WewerehavingonlylimitedoptionsavailableforerrorhandlinginClassicASPsuchas,"OnErrorResumeNext".InASP3.0wesawthenewASPobjectcalledErrorObject.Butwewerenotabletohandleallexception/errorsefficiently.NowinASP.NETwehaveanewerrorhandlingmechanismwhichwasalreadytheirinotherlanguagessuchasC,C++andJAVA.Wecanalsocallthetry...catchmechanismas"ExceptionHandling"

WhatisTry...Catch....Finally

ThisisanewerrorhandlingmechanisminVB.NET,soasinASP.NET.Wellwehavethreeblocksofcode,wereeachblockhasitownfunctionality.TheTry...Catch...Finallyblockofcodesurroundsthecodewhereanexceptionmightoccur.ThesimpleTrystatementcomesbeforetheblockofcode,theCatchblockofcodeiswherewespecifywhattypeoferrortolookfor,andtheFinallyblockofcodeisalwaysexecutedandcontainscleanuproutinesforexceptionsituations.Sincethecatchblockisspecifictothetypeoferrorwewanttocatch,wewilloftenusemultipleCatchblocksinourTry...Catch...Finallystructure.

AsimpleDatabaseoperation

DimmySqlConnectionasNewSqlConnection(ConnectionString)

DimmySqlCommandasSqlCommand

DimstrSqlasString

strSql="insertintoyourtable(f1,f2)values('f1','f2')"

mySqlCommand=newSqlCommand(strSql,mySqlConnection)

Try

mySqlConnection.Open()

mySqlCommand.ExecuteReader(CommandBehavior.CloseConnection)

Message.text="NewForwardinformationadded"

CatchSQLexcassqlexception

Message.text=Message.text+sqlexc.tostring()

Catchexcasexception

ifInstr(1,exc.tostring,"duplicatekey")>0then

Message.text=Message.text+"Cannotinsertduplicatevalues."

else

Message.text=Message.text+exc.tostring()

endif

Finally

mySqlConnection.Close()

EndTry

Whatdoestheaboveexampleexactlydo?

Well,intheaboveexampleweweretryingtoinsertsomevaluestoadatabasetable.Thepossiblechanceswhileperformingadatabaseoperationareinvalidconnectionstring,databaseservertoobusyresultinginconnectiontimeout,databaseservernotcurrentlyrunningetcetc.Weshouldanticipatealltheseerrorswhileperformingadatabaseoperation.So,wehaveaTryblock,whichcontainsthestatementssuchasopeningtheconnectionandexecutingtheoperation.Basically,wehavetwomajorstatementsinsidethetryblockwhichmayresultinanexception/error.

AsIsaid,anyexceptioncanoccurduringadatabaseoperation.CatchingalltheseexceptionisnowveryeasywiththeCatchblock.AllweneedistohaveaCatchblock.WecanhaveanynumberofCatchblocks.EachCatchblockmayhaveadifferenterror/exceptiontrappingmechanism.Intheaboveexample,wehavetwocatchblocks,onewhichcapturesageneralexceptionandtheotheronewhichtrapstheSqlException.

Whenallthestatementsinsidethecatchblocksareexecuted,thefinallyblockcomesintothepicture.AsIsaidearlier,finallyblockcontainscleanuproutinesforexceptionsituations.

ExitTrystatement

WecanalsohavetheExitTrystatementinsideanyofthetry...catchblock.TheobjectiveofthisstatementistobreakoutoftheTryorCatchblock.OncetheExitTrystatementisexecuted,thecontrolgoestotheFinallyblock.So,ExitTrystatementcanbebestusedwereweneedtoexecutethecleanuproutines.

HowaboutnestedTrystatments?

WecanhavenestedTryandCatchblocks.Canyouimagine,whenweshouldusenestedtrystatements.Well,errorscanoccurwithintheCatchportionoftheTrystructures,andcausefurtherexceptiontooccur.TheabilitytonesttrystructuresisavailablesothatwecanuseasecondTrystructuretocoverexceptions.

Links

http://www.vbweb.co.uk/show/1889/2/http://www.oreillynet.com/pub/a/dotnet/2001/09/04/error_handling.html?page=2