电子商务毕业论文外文翻译范文《JavaandtheInternet》.docx

电子商务毕业论文外文翻译范文《JavaandtheInternet》.docx

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电子商务毕业论文外文翻译范文《JavaandtheInternet》

外文文献:

JavaandtheInternet

IfJavais,infact,yetanothercomputerprogrammingIanguage,youmayquestionwhyitissoimportantandwhyitisbeingpromotedasarevolutionarystepincomputerprogramming.Theanswerisn'timmediatelyobviousifyou'recomingfromatraditionalprogrammingperspective.AlthoughJavaisveryusefulforsolvingtraditionalstand-aloneprogrammingproblems,itisalsoimportantbecauseitwillsolveprogrammingproblemsontheWorldWideWeb.

1.Client-sideprogramming

TheWeb'sinitialserver-browserdesignprovidedforinteractivecontent,buttheinteractivitywascompletelyprovidedbytheserver.Theserverproducedstaticpagesfortheclientbrowser,whichwouldsimplyinterpretanddisplaythem.BasicHTMLcontainssimplemechanismsfordatagathering:

text-entryboxes,checkboxes,radioboxes,listsanddrop-downlists,aswellasabuttonthatcanonlybeprogrammedtoresetthedataontheformorsubmit”thedataontheformbacktotheserver.ThissubmissionpassesthroughtheCommonGatewayInterface（CGI）providedonallWebservers.ThetextwithinthesubmissiontellsCGIwhattodowithit.Themostcommonactionistorunaprogramlocatedontheserverinadirectorythat'stypicallycalledcgi-bin.”（IfyouwatchtheaddresswindowatthetopofyourbrowserwhenyoupushabuttononaWebpage,youcansometimesseecgi-bin”withinallthegobbledygookthere.）TheseprogramscanbewritteninmostIanguages.Perlisacommonchoicebecauseitisdesignedfortextmanipulationandisinterpreted,soitcanbeinstalledonanyserverregardlessofprocessororoperatingsystem.

ManypowerfulWebsitestodayarebuiltstrictlyonCGI,andyoucaninfactdonearlyanythingwithit.However,WebsitesbuiltonCGIprogramscanrapidlybecomeoverlycomplicatedtomaintain,andthereisalsotheproblemofresponsetime.TheresponseofaCGIprogramdependsonhowmuchdatamustbesent,aswellastheloadonboththeserverandtheInternet.（Ontopofthis,startingaCGIprogramtendstobeslow.）TheinitialdesignersoftheWebdidnotforeseehowrapidlythisbandwidthwouldbeexhaustedforthekindsofapplicationspeopledeveloped.Forexample,anysortofdynamicgraphingisnearlyimpossibletoperformwithconsistencybecauseaGIFfilemustbecreatedandmovedfromtheservertotheclientforeachversionofthegraph.Andyou'enodoubthaddirectexperieneewithsomethingassimpleasvalidatingthedataonaninputform.Youpressthesubmitbuttononapage;thedataisshippedbacktotheserver;theserverstartsaCGIprogramthatdiscoversanerror,formatsanHTMLpageinformingyouoftheerror,andthensendsthepagebacktoyou;youmustthenbackupapageandtryagain.Notonlyisthisslow,it'sinelegant.

Thesolutionisclient-sideprogramming.MostmachinesthatrunWebbrowsersarepowerfulenginescapableofdoingvastwork,andwiththeoriginalstaticHTMLapproachtheyaresittingthere,justidlywaitingfortheservertodishupthenextpage.Client-sideprogrammingmeansthattheWebbrowserisharnessedtodowhateverworkitcan,andtheresultfortheuserisamuchspeedierandmoreinteractiveexperieneeatyourWebsite.

Theproblemwithdiscussionsofclient-sideprogrammingisthattheyaren'tverydifferentfromdiscussionsofprogrammingingeneral.Theparametersarealmostthesame,buttheplatformisdifferent:

aWebbrowserislikealimitedoperatingsystem.Intheend,youmuststillprogram,andthisaccountsforthedizzyingarrayofproblemsandsolutionsproducedbyclient-sideprogramming.Therestofthissectionprovidesanoverviewoftheissuesandapproachesinclient-sideprogramming.

2.Plug-ins

Oneofthemostsignificantstepsforwardinclient-sideprogrammingisthedevelopmentoftheplug-in.Thisisawayforaprogrammertoaddnewfunctionalitytothebrowserbydownloadingapieceofcodethatplugsitselfintotheappropriatespotinthebrowser.Ittellsthebrowserfromnowonyoucanperformthisnewactivity.”（Youneedtodownloadtheplug-inonlyonce.）Somefastandpowerfulbehaviorisaddedtobrowsersviaplug-ins,butwritingaplug-inisnotatrivialtask,andisn'somethingyou'dwanttodoaspartoftheprocessofbuildingaparticularsite.Thevalueoftheplug-inforclient-sideprogrammingisthatitallowsanexpertprogrammertodevelopanewIanguageandaddthatIanguagetoabrowserwithoutthepermissionof

thebrowsermanufacturer.Thus,plug-insprovideabackdoor”thatallowsthecreationofnewclient-sideprogrammingIanguages（althoughnotallIanguagesareimplementedasplug-ins）.

3.Scriptinglanguages

Plug-insresultedinanexplosionofscriptingIanguages.WithascriptingIanguageyouembedthesourcecodeforyourclient-sideprogramdirectlyintotheHTMLpage,andtheplug-inthatinterpretsthatIanguageisautomaticallyactivatedwhiletheHTMLpageisbeingdisplayed.ScriptingIanguagestendtobereasonablyeasytounderstandand,becausetheyaresimplytextthatispartofanHTMLpage,theyloadveryquicklyaspartofthesingleserverhitrequiredtoprocurethatpage.Thetrade-offisthatyourcodeisexposedforeveryonetosee（andsteal）.Generally,however,youaren'tdoingamazinglysophisticatedthingswithscriptingIanguagessothisisnottoomuchofahardship.

ThispointsoutthatthescriptingIanguagesusedinsideWebbrowsersarereallyintendedtosolvespecifictypesofproblems,primarilythecreationofricherandmoreinteractivegraphicaluserinterfaces（GUIs）.However,ascriptingIanguagemightsolve80percentoftheproblemsencounteredinclient-sideprogramming.Yourproblemsmightverywellfitcompletelywithinthat80percent,andsincescriptingIanguagescanalloweasierandfasterdevelopment,youshouldprobablyconsiderascriptingIanguagebeforelookingatamoreinvoIvedsolutionsuchasJavaorActiveXprogramming.

ThemostcommonlydiscussedbrowserscriptingIanguagesareJavaScript（whichhasnothingtodowithJava;it'namedthatwayjusttograbsomeofJava'smarketingmomentum）,VBScript（whichlookslikeVisualBasic）,andTcl/Tk,whichcomesfromthepopularcross-platformGUI-buildingIanguage.Thereareothersoutthere,andnodoubtmoreindevelopment.

JavaScriptisprobablythemostcommonlysupported.ItcomesbuiltintobothNetscapeNavigatorandtheMicrosoftInternetExplorer（IE）.Inaddition,thereareprobablymoreJavaScriptbooksavailablethantherearefortheotherbrowserIanguages,andsometoolsautomaticallycreatepagesusingJavaScript.However,ifyou'realreadyfluentinVisualBasicorTcl/Tk,you'

bemoreproductiveusingthosescriptingIanguagesratherthanlearninganewone.（You'haveyourhandsfulldealingwiththeWebissuesalready.）

4.Java

IfascriptingIanguagecansolve80percentoftheclient-sideprogrammingproblems,whatabouttheother20percen—thereallyhardstuff?

”ThemostpopularsolutiontodayisJava.NotonlyisitapowerfulprogrammingIanguagebuilttobesecure,cross-platform,andinternational,butJavaisbeingcontinuallyextendedtoprovideIanguagefeaturesandlibrariesthatelegantlyhandleproblemsthataredifficultintraditionalprogrammingIanguages,suchasmultithreading,databaseaccess,networkprogramming,anddistributedcomputing.Javaallowsclient-sideprogrammingviatheapplet.

Anappletisamini-programthatwillrunonlyunderaWebbrowser.TheappletisdownloadedautomaticallyaspartofaWebpage（justas,forexample,agraphicisautomaticallydownloaded）.Whentheappletisactivateditexecutesaprogram.Thisispartofitsbeauty—itprovidesyouwithawaytoautomaticallydistributetheclientsoftwarefromtheserveratthetimetheuserneedstheclientsoftware,andnosooner.Theusergetsthelatestversionoftheclientsoftwarewithoutfailandwithoutdifficultreinstallation.BecauseofthewayJavaisdesigned,theprogrammerneedstocreateonlyasingleprogram,andthatprogramautomaticallyworkswithallcomputersthathavebrowserswithbuilt-inJavainterpreters.（Thissafelyincludesthevastmajorityofmachines.）SinceJavaisafull-fledgedprogrammingIanguage,youcandoasmuchworkaspossibleontheclientbeforeandaftermakingrequestsoftheserver.Forexample,youwon'needtosendarequestformacrosstheInternettodiscoverthatyovegottenadateorsomeotherparameterwrong,andyourclientcomputercanquicklydotheworkofplottingdatainsteadofwaitingfortheservertomakeaplotandshipagraphicimagebacktoyou.Notonlydoyougettheimmediatewinofspeedandresponsiveness,butthegeneralnetworktrafficandloadonserverscanbereduced,preventingtheentireInternetfromslowingdown.

OneadvantageaJavaapplethasoverascriptedprogramisthatit'incompiledform,sothesourcecodeisn'availabletotheclient.Ontheother

hand,aJavaappletcanbedecompiledwithouttoomuchtrouble,buthidingyourcodeisoftennotanimportantissue.Twootherfactorscanbeimportant.Asyouwillseelaterinthisbook,acompiledJavaappletcancomprisemanymodulesandtakemultipleserverhits”（accesses）todownload.（InJava1.1andhigherthisisminimizedbyJavaarchives,calledJARfiles,thatallowalltherequiredmodulestobepackagedtogetherandcompressedforasingledownload.）AscriptedprogramwilljustbeintegratedintotheWebpageaspartofitstext（andwillgenerallybesmallerandreduceserverhits）.Thiscouldbeimportanttoth