JAVA外文文献+翻译.docx

JAVA外文文献+翻译.docx

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JAVA外文文献+翻译

JavaandtheInternet

IfJavais，infact，yetanothercomputerprogramminglanguage,youmayquestionwhyitissoimportantandwhyitisbeingpromotedasarevolutionarystepincomputerprogramming。

Theanswerisn’timmediatelyobviousifyou'recomingfromatraditionalprogrammingperspective。

AlthoughJavaisveryusefulforsolvingtraditionalstand-aloneprogrammingproblems，itisalsoimportantbecauseitwillsolveprogrammingproblemsontheWorldWideWeb。

1.Client—sideprogramming

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

text-entryboxes，checkboxes，radioboxes，listsanddrop-downlists,aswellasabuttonthatcanonlybeprogrammedtoresetthedataontheformor“submit”thedataontheformbacktotheserver.ThissubmissionpassesthroughtheCommonGatewayInterface（CGI）providedonallWebservers.ThetextwithinthesubmissiontellsCGIwhattodowithit。

Themostcommonactionistorunaprogramlocatedontheserverinadirectorythat'stypicallycalled“cgi—bin.”（IfyouwatchtheaddresswindowatthetopofyourbrowserwhenyoupushabuttononaWebpage,youcansometimessee“cgi-bin”withinallthegobbledygookthere。

）Theseprogramscanbewritteninmostlanguages。

Perlisacommonchoicebecauseitisdesignedfortextmanipulationandisinterpreted,soitcanbeinstalledonanyserverregardlessofprocessororoperatingsystem.

ManypowerfulWebsitestodayarebuiltstrictlyonCGI，andyoucaninfactdonearlyanythingwithit。

However，WebsitesbuiltonCGIprogramscanrapidlybecomeoverlycomplicatedtomaintain,andthereisalsotheproblemofresponsetime。

TheresponseofaCGIprogramdependsonhowmuchdatamustbesent,aswellastheloadonboththeserverandtheInternet.（Ontopofthis，startingaCGIprogramtendstobeslow.）TheinitialdesignersoftheWebdidnotforeseehowrapidlythisbandwidthwouldbeexhaustedforthekindsofapplicationspeopledeveloped.Forexample,anysortofdynamicgraphingisnearlyimpossibletoperformwithconsistencybecauseaGIFfilemustbecreatedandmovedfromtheservertotheclientforeachversionofthegraph.Andyou’venodoubthaddirectexperiencewithsomethingassimpleasvalidatingthedataonaninputform。

Youpressthesubmitbuttononapage；thedataisshippedbacktotheserver;theserverstartsaCGIprogramthatdiscoversanerror，formatsanHTMLpageinformingyouoftheerror，andthensendsthepagebacktoyou;youmustthenbackupapageandtryagain。

Notonlyisthisslow，it’sinelegant.

Thesolutionisclient-sideprogramming。

MostmachinesthatrunWebbrowsersarepowerfulenginescapableofdoingvastwork,andwiththeoriginalstaticHTMLapproachtheyaresittingthere,justidlywaitingfortheservertodishupthenextpage.Client-sideprogrammingmeansthattheWebbrowserisharnessedtodowhateverworkitcan,andtheresultfortheuserisamuchspeedierandmoreinteractiveexperienceatyourWebsite.

Theproblemwithdiscussionsofclient-sideprogrammingisthattheyaren'tverydifferentfromdiscussionsofprogrammingingeneral。

Theparametersarealmostthesame,buttheplatformisdifferent：

aWebbrowserislikealimitedoperatingsystem.Intheend,youmuststillprogram,andthisaccountsforthedizzyingarrayofproblemsandsolutionsproducedbyclient—sideprogramming。

Therestofthissectionprovidesanoverviewoftheissuesandapproachesinclient—sideprogramming.

2.Plug-ins

Oneofthemostsignificantstepsforwardinclient—sideprogrammingisthedevelopmentoftheplug—in。

Thisisawayforaprogrammertoaddnewfunctionalitytothebrowserbydownloadingapieceofcodethatplugsitselfintotheappropriatespotinthebrowser.Ittellsthebrowser“fromnowonyoucanperformthisnewactivity。

"（Youneedtodownloadtheplug—inonlyonce.）Somefastandpowerfulbehaviorisaddedtobrowsersviaplug—ins,butwritingaplug—inisnotatrivialtask,andisn’tsomethingyou'dwanttodoaspartoftheprocessofbuildingaparticularsite。

Thevalueoftheplug—inforclient—sideprogrammingisthatitallowsanexpertprogrammertodevelopanewlanguageandaddthatlanguagetoabrowserwithoutthepermissionofthebrowsermanufacturer.Thus，plug—insprovidea“backdoor”thatallowsthecreationofnewclient-sideprogramminglanguages（althoughnotalllanguagesareimplementedasplug-ins）.

3。

Scriptinglanguages

Plug-insresultedinanexplosionofscriptinglanguages.Withascriptinglanguageyouembedthesourcecodeforyourclient-sideprogramdirectlyintotheHTMLpage，andtheplug-inthatinterpretsthatlanguageis