ASP编程：使用global.asp准时实行ASP

ActiveServerPage技术为应用开发商提供了基于脚本的直观、快速、高效的应用开发手段，极大地提高了开发的效果。在讨论ASP的安全性问题之前，让我们来看看ASP是怎么工作的。准时|实行Usingtheglobal.asatoscheduleASPcodeexecution.
Haveyoueverhadsomeaspcodethatneededtoexecuteeveryonceinawhilebut,youjustdidntknowhowtodoit.

Thereisasolutionthatdoesntinvolverunninganyschedulingorscriptingsoftwareontheserverandisactuallyveryeasytogetworking.

Yousee...thereisthingcalledthe"global.asa".MostASPnewbiesprobablywonderwhattheheckitevenis.TheGlobal.asafileiseventdriven.Itcancontainfoureventprocedures:Application_OnStart,Application_OnEnd,Session_OnStart,andSession_OnEnd.

Theglobal.asaisbasicallyloadedintomemorythefirsttimeanyuserviewsapageonyourWebapplication.Thereareeventprocedurestubsthatcancontainscriptyouwanttobeexecutedwhentheapplicationstartsorends,orwhenthesessionstartsorends.

Withsometrickycodingyoucanusethisfiletoschedulecodetoexecute.Atleastaroundthetimeyouneeditto,thiswontbeabletomakeitexecuteatexactlyacertaintime.

Hereisthe1stexample.Itsimplykeepstrackofhowmanyvisitorshavebeentoyoursiteandafter100itresetsthecountbackto0andexecuteswhatevercodeyouneedtorun.Obviouslyyoullneedtoadjustthe"100"towhatevermakessensefortheamountofvisitorsyoursitereceives.

Contentsoftheglobal.asaarebelow.

<SCRIPTLANGUAGE=VBScriptRUNAT=Server>

SubApplication_OnStart
Application("SessionCount")=0
EndSub

SubSession_OnStart

Application.Lock
Application("SessionCount")=Application("SessionCount")+1
Application.Unlock

IfApplication("SessionCount")>100Then

Application.Lock
Application("SessionCount")=0
Application.Unlock

Hereyouwouldputanycodeyouneedtorun
donotsurroundthecodewith<%%>tags
Forexampleyoumightrunadatabasequerythatchecksforexpiredaccounts

Endif

EndSub

</SCRIPT>

Nowletssayyouwantsomethingtoexecute4timesaday.Youcanstorethedate&timeinatextfileandcheckitperiodically.Whenthedateandtimegettobemorethan6hoursoldthecodewillwritethenewdate&timetothetextfileandthenexecutethecodeyouwanttorun.Youcouldchangethe"6"towhateveryouwantandthereforeexecutethecodemoreorlessoften,

Thisisaprettyslicksolutionthoughitrequirescorrectpermissionstothetextfileforreading&writing.Ifnotyoullgetanerror.

Inthisexamplewearecheckingthetextfileevery15visitors.Youcanadjustthisamountorremovethe"check"completelysothatitchecksthefileeverytime,butwhycheckthefileeverytimewhenyouhaveaverybusysite?Thatwouldjustbeawasteofserverresources,butitisuptoyouhowfaryouwanttotakethis.

Inthisexampleyouneedtostartthetextfileoffwithavaliddate&timeorelseyouwillgetanerrorbecausethescriptwillreadinanemptyvaluethe1sttime.

EXAMPLE:put6/30/996:58:45PMinthe1stlineofthetextfile.

Youcouldaddcodetocheckforthatandhandletheerror,butIdidntreallycareatthetimesoIdidntdothat.Aslongasthereisadatetherewhenitstartsitwillkeepworking.

Contentsoftheglobal.asaarebelow.

<SCRIPTLANGUAGE=VBScriptRUNAT=Server>

SubApplication_OnStart
Application("SessionCount")=0
EndSub

SubSession_OnStart

Application.Lock
Application("SessionCount")=Application("SessionCount")+1
Application.Unlock

IfApplication("SessionCount")>15Then

Application.Lock
Application("SessionCount")=0
Application.Unlock

SetObjMyFile=CreateObject("Scripting.FileSystemObject")
SetOpenMyFile=ObjMyFile.OpenTextFile(Server.MapPath("last-update.txt"))
MyFileValue=OpenMyFile.ReadLine
OpenMyFile.Close

IfDateDiff("h",MyFileValue,NOW)>6Then

Hereyouwouldputanycodeyouneedtorun
donotsurroundthecodewith<%%>tags
Forexampleyoumightrunadatabasequerythatchecksforexpiredaccounts

SetWriteMyFile=ObjMyFile.CreateTextFile(Server.MapPath("last-update.txt"))
WriteMyFile.WriteLine(NOW)
WriteMyFile.Close

Endif
EndIf

EndSub
</p>ASP最大的缺点在于网络的安全性和可靠性，企业将经营数据放在开放的平台上，最大的担忧就是如何保证这些数据不被其他人破坏。

Server:这个表示的服务器，操作服务器的一些东西使用这个，如Server.Mappath转换服务器路径,Server.CreateObject实例化一个组件

仓酷云

封装性使得代码逻辑清晰，易于管理，并且应用到ASP.Net上就可以使业务逻辑和Html页面分离，这样无论页面原型如何改变，业务逻辑代码都不必做任何改动；继承性和多态性使得代码的可重用性大大提高。

以上是语言本身的弱点，在功能方面ASP同样存在问题，第一是功能太弱，一些底层操作只能通过组件来完成，在这点上是远远比不上PHP/JSP，其次就是缺乏完善的纠错/调试功能，这点上ASP/PHP/JSP差不多。

代码逻辑混乱，难于管理：由于ASP是脚本语言混合html编程，所以你很难看清代码的逻辑关系，并且随着程序的复杂性增加，使得代码的管理十分困难，甚至超出一个程序员所能达到的管理能力，从而造成出错或这样那样的问题。

它可通过内置的组件实现更强大的功能，如使用A-DO可以轻松地访问数据库。

代码的可重用性差：由于是面向结构的编程方式，并且混合html，所以可能页面原型修改一点，整个程序都需要修改，更别提代码重用了。

在平时的学习过程中要注意现学现用，注重运用，在掌握了一定的基础知识后，我们可以尝试做一些网页，也许在开始的时候我们可能会遇到很多问题，比如说如何很好的构建基本框架。

另外因为asp需要使用组件，所以了解一点组件的知识(ADODB也是组件)

Request:从字面上讲就是“请求”，因此这个是处理客户端提交的东东的,例如Resuest.Form，Request.QueryString,或者干脆Request("变量名")