计算机专业文献翻译功能强大的ASPHTML转换工具.docx

计算机专业文献翻译功能强大的ASPHTML转换工具.docx

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计算机专业文献翻译功能强大的ASPHTML转换工具

英文翻译

CuttingEdgeAClient-sideEnvironmentforASPPages

ASPisaWebtechnologythatreliesspecificallyoncapabilitiesofMicrosoft?

InternetInformation

Services（IIS）.Forthisreason,veryfewcommercialproductshaveattemptedtoprovideanASP-to-HTMLconverter.TheproblemwithsuchconvertersisthatyoumustworkinconjunctionwiththeWebservertotriggertheASPparserandfindtheintrinsicobjectsavailable.Whenyoudouble-clickonanHTMLpagefromtheExplorershell,yousimplyaskthebrowsertoretrieveandrenderthesourcecodeofthefile.However,whenyoudouble-clickonanASPfilefromExplorer,youcannotaskthebrowsertotranslateitintoHTML.

PracticalReasonsforanASPConverter

OK,soanASP-to-HTMLconvertermightnotbethetoolthatthousandsofprogrammersdreamofeverynight.

However,Icanenvisionatleastacoupleofscenarioswheresuchatoolwouldbeveryhandy.Thefirst

scenariowasmentionedbyRobertHessintheApril2000WebQ&Acolumn.SupposeyouhaveseveralpagesthatrequiresomeinteractionwithadatabaseonafrequentlyvisitedWebsite.WritingthemasASPpageslooksliketheperfectsolution.However,ifthedatabaseisnotveryvolatileandthepageoutputisnothighlydependentontheuser'sinput,youcouldeasilyresorttoplainoldHTMLforbetterperformance.

Forexample,alistofsuppliersisprobablythekindofdatathatyouwouldupdateonlyafewtimesa

year.Whyrebuildthatlistontheflyeachtimeit'srequested,whenastaticHTMLpagewouldincurless

overhead?

AnASP-to-HTMLtoolcouldbeusedasakindofbatchcompilerforASPpages.Youwritethemasserver-sideresources,andthenwhenyourealizetheyarenotparticularlydependentonruntimeconditions,youcantransformthemintostaticHTMLpageswitheitherthe.aspor.htm

（1）extension.

WhileI'monthesubject,letmepointoutasignificantimprovementinthemanagementofscriptlessASPpagesthat'savailablewithIIS5.0.UntilIIS4.0,allresourceswitha.aspextensionweresubjectto

parsing,whetherornottheycontainedscriptcode.WithIIS5.0thisdrawbackhasbeeneliminatedasIIS

checksfor<%...%>blocksbeforeloadingtheASPparser.

AnASP-to-HTMLconverterwouldalsobehandywhenyouneedtoviewASPpagesoffline.Forexample,aclientrecentlyaskedmeaboutthepossibilityofusingasingledevelopmentenvironmentforbuildingbothWebsitesandCDs.IfirstconsideredusingstaticHTMLpagesthatcouldbeviewedovertheWeborinalocalbrowser,buttheideawassoondismissedgiventhecomplexityandtheamountofcontentinvolved.Also,myclientcouldnotguaranteeanyparticularsoftwareconfigurationontheuser'smachine,andtheonlyproductthatcouldbesuppliedwiththeCDswasMicrosoftInternetExploreroracustomWebbrowser.

ASPlookedlikethenaturalchoicefortheWebsideoftheproject,butwhatabouttheCD?

TomakeASPworkofflinewithoutaWebserver,youneedcodethatextractsallthe<%¡%>codeblocksfromthepageandprocessesthem.Inaddition,thismodulewouldhavetoprovideasimulatedASPobjectmodelandtakecareofcollectingtheportionsofplainHTMLtext.Thenitwouldhavetoputitalltogether,combiningthestaticHTMLcodewiththeoutputoftheprocessedscripts.

Inthiscolumn,IwilldiscussthearchitectureoftheofflineASPviewerandsomeimplementationdetails.Inparticular,I'llshowyouhowtoemulatethebehavioroftheASPResponseobject.Nextmonth,I'llfinishupthecode,coveringRequestandServerplussomeotherrelatedtopics.Thismonth'scodeshowsthepotentialofthisapproachandworkswithtypicalASPpages,thoughitisnotcomprehensive.Iwon'tcoverotherASPobjectssuchasSessionorApplicationbecausetheyarerarelyneededinlocalscenarios.

TheBrowser'sRole

ToemulateASPwhileworkingoffline,youneedalittlehelpfromthebrowser.Basically,thebrowsermustbeabletodetectwhetherthepagetowhichit'sabouttonavigateisaURLoralocalpathnameand

whetheritcontainsthe.aspextension.IftheuseriscallingaURL,thebrowserdoeswhatitwould

normallydo.Otherwise,itcallsacustommoduletolocallyparsethecontentoftheASPfile.

Furthermore,thebrowserisinvolvedwhentheASPpagethatwillbeemulatedcontainsformsand

hyperlinks.（I'lldiscussthisfurthernextmonth.）Giventheserequirements,todealwithASPpages

offlineyouneedacustomizedversionofthebrowser.WhilesubclassingInternetExplorerorNetscape

Communicatorisalwayspossible,IsuggestyouwriteabrandnewbrowserfromscratchusingexistingWebbrowsertechnologysuchastheMicrosoftWebBrowsercontrol.WhileI'lluseVisualBasic?

here,youcanalsouseC++.AsagoodstartingpointinC++,youcantrytheMFCIEorATLBrowsersamples,bothofwhichcomewiththelatestPlatformSDK.InFigure1youcanseethelayoutofthebrowser.Forillustration,I'vedividedtheclientareaintothreeblocks:

onefortheactualHTMLrendering,onefortheoriginalASPtext,andonefortheexpandedHTMLtext.Figure2showsthecodeforthebrowser.

Figure1TheCustomASPBrowser?

?

Duringtheform'sinitialization,anewCAspParserobjectiscreatedandsettoworkproperly.Onceyou've

clickedtheGobutton,thebrowserdetectswhetheryou'recallingtheASPpagelocallyoroverHTTP,and

actsaccordingly.AllthelogicishiddenintheCAspParserclass,whichexposesthreepublicfunctions:

Initialize,SetscriptControl,andParseTextToFile.Initializemakessurethescriptingenvironmentis

properlyinitializedandreadytowork.ThroughSetscriptControl,theclassreceivestheworkinginstance

ofthescriptenvironment（moreonthislater）.ParseTextToFileparsesthecontentofthegivenASPfile

andcreatesanoutputstream.Basically,theparserreadsthewholecontentoftheASPfileintomemory

andthenwalksthroughit.Itlocatesanyoccurrenceof"<%",thencopiesthetextthatprecedes"<%"to

theoutputbuffer,andstartsanewsearchfortheclosingtag,"%>".Thecommandtextisextractedand

processedseparately.Anyoutputisthenappendedtotheresponsebuffer.

ThescriptcodeinthebodyofanASPpagemaycontainreferencestotheintrinsicobjectsthatformtheASPobjectmodel.Thesewell-knownobjectsarelistedinFigure3.IISisresponsibleformakingthese

objects¡ªplustwomore:

ASPErrorandObjectContext¡ªavailableinthescript'snamespacewhentheparserisabouttoprocessthecontentofthevariouscodeblocks.ToobtainanASPparserthatworksoutsidethe

Webserver,youshouldprovideareplacementfortheseobjects,whichmeansbuildingaclient-sideASP

objectmodel.

AClient-sideASPObjectModel

OneoftheproblemswithWebapplicationsistheinabilitytomaintainstatewhenworkingoverHTTP.Stateistheabilitytoassociatevariablesandobjectswithaparticularuser.Atooltostoreindividual

settingsandresourcescansolvetheproblem.ThisiswhattheSessionandApplicationobjectsprovide,

albeitatdifferentlevels.Butyoudon'talwaysneedtoimplementthisfeatureinaclient-sideASP

objectmodel.Infact,alocalASPpageisnormallyaccessedbyoneuseratatimeandstatemanagementis

afarlessimportantissue.

FromtheperspectiveofanofflineASPviewer,thekeyASPobjectsareResponseandRequestbecausetheyprovidethebasicfunctionalitythatmakeapageinteractwiththerestoftheworld.Whetheryouneedtoimplementallorapartofthestandardmethodsandpropertiesdependsonyourparticularproject.

AlthoughASPistightlyintegratedwithIISandMicrosoftTransactionServices（MTS）,andCOM+

environments,thisdoesn'tmeanthatyoucannotuseaunified,yetASP-basedapproachfortheconcurrent

developmentofproductsthatdelivercontentthroughdifferentmedia（liketheWebandCDs）.OfflinepagesconsumedwithouttheinterventionoftheWebserverarenormallymuchsimpleranddon'tneedallthefeaturesofanonlineWebapplication.Basedonmypersonalexperience,Isuggestyouimplementaminimalsetoffeatures（similartothoseIdiscusshere）andthenextendthesetwhenyourpagesneedtosupport

extraASPfeatures.

IdeployedthefirstversionofmyprojectwithonlyResponseandRequestobjects.Inparticular,Ionly

implementedtheWritemethodoftheResponseobject,andjustfortheHTMLcontenttype.Requestonly

exposedtheQueryStringcollection.Inasecondstep,IaddedsupportforResponse.EndandtheRequest's

FormandServerVariablescollections.Later,Ialsoaddedsomespecialfeaturessuchasnewenvironment

variablesandnewoffline-onlyobjects,includingscripting.FileSystemObject.

ThekeyquestionsconcernhowyousimulatetheResponseorRequestobjectandhowyourunallthescriptcodethatanASPfilecontains.Toexecutescriptcode,youcaneithertakeadvantageoftheMicrosoftscriptControl¡ªadownloadablecomponent（seeorusetherawWindowsscriptCOMinterfaces.Foraprimer,lookattheExtremeC++columnintheAugust1997issueofMicrosoftInternetDeveloper.SinceI'mdevelopinganapplicationinVisualBasic,usingthescriptControlisthenaturalchoice.

ThescriptControlscriptControlisanActiveX?

controlwithoutauserinterfacethatwrapsalltheWindowsscriptinterfacesneededfordialogwithascriptlanguageparser.IthasaLanguagepropertythroughwhichyouselectalanguage.VBscriptandJscript?

arethetwousualoptions,butprovidedyouhaveacompliantparser,anyscriptinglanguageisfine.FrancescoBalenacoveredthescriptControlindetailintheJuly1999issueofMIND（see"ExploringtheMicrosoftscriptControl"）.TobiasMartinsson'sarticle,"A