JSP技术概述与应用框架外文翻译.doc
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JSP技术概述与应用框架外文翻译.doc
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大连交通大学2012届本科生毕业设计(论文)外文翻译
外文原文
OverviewofJSPTechnologyandJSPapplicationframeworks
Autor:
ZambonGiulio/SeklerMichael
Source:
Springer-VerlagNewYorkInc
1.BenefitsofJSP
JSPpagesaretranslatedintoservlets.So,fundamentally,anytaskJSPpagescanperformcouldalsobeaccomplishedbyservlets.However,thisunderlyingequivalencedoesnotmeanthatservletsandJSPpagesareequallyappropriateinallscenarios.Theissueisnotthepowerofthetechnology,itistheconvenience,productivity,andmaintainabilityofoneortheother.Afterall,anythingyoucandoonaparticularcomputerplatformintheJavaprogramminglanguageyoucouldalsodoinassemblylanguage.Butitstillmatterswhichyouchoose.JSPprovidesthefollowingbenefitsoverservletsalone:
•ItiseasiertowriteandmaintaintheHTML.YourstaticcodeisordinaryHTML:
noextrabackslashes,nodoublequotes,andnolurkingJavasyntax.
•YoucanusestandardWeb-sitedevelopmenttools.EvenHTMLtoolsthatknownothingaboutJSPcanbeusedbecausetheysimplyignoretheJSPtags.
•Youcandivideupyourdevelopmentteam.TheJavaprogrammerscanworkonthedynamiccode.TheWebdeveloperscanconcentrateonthepresentationlayer.Onlargeprojects,thisdivisionisveryimportant.Dependingonthesizeofyourteamandthecomplexityofyourproject,youcanenforceaweakerorstrongerseparationbetweenthestaticHTMLandthedynamiccontent.
Now,thisdiscussionisnottosaythatyoushouldstopusingservletsanduseonlyJSPinstead.Bynomeans.Almostallprojectswilluseboth.Forsomerequestsinyourproject,youwilluseservlets.Forothers,youwilluseJSP.Forstillothers,youwillcombinethemwiththeMVCarchitecture.Youwanttheappropriatetoolforthejob,andservlets,bythemselves,donotcompleteyourtoolkit.
2.AdvantagesofJSPOverCompetingTechnologies
Anumberofyearsago,Martywasinvitedtoattendasmall20-personindustryroundtablediscussiononsoftwaretechnology.SittingintheseatnexttoMartywasJamesGosling,inventoroftheJavaprogramminglanguage.Sittingseveralseatsawaywasahigh-levelmanagerfromaverylargesoftwarecompanyinRedmond,Washington.Duringthediscussion,themoderatorbroughtupthesubjectofJini,whichatthattimewasanewJavatechnology.Themoderatoraskedthemanagerwhathethoughtofit,andthemanagerrespondedthatitwastooearlytotell,butthatitseemedtobeanexcellentidea.Hewentontosaythattheywouldkeepaneyeonit,andifitseemedtobecatchingon,theywouldfollowhiscompany'susual"embraceandextend"strategy.Atthispoint,Goslinglightheartedlyinterjected"Youmeandisgraceanddistend."
Now,thegrievancethatGoslingwasairingwasthathefeltthatthiscompanywouldtaketechnologyfromothercompaniesandsubornitfortheirownpurposes.Butguesswhat?
Theshoeisontheotherfoothere.TheJavacommunitydidnotinventtheideaofdesigningpagesasamixtureofstaticHTMLanddynamiccodemarkedwithspecialtags.Forexample,ColdFusiondidityearsearlier.EvenASP(aproductfromtheverysoftwarecompanyoftheaforementionedmanager)popularizedthisapproachbeforeJSPcamealonganddecidedtojumponthebandwagon.Infact,JSPnotonlyadoptedthegeneralidea,itevenusedmanyofthesamespecialtagsasASPdid..So,thequestionbecomes:
whyuseJSPinsteadofoneoftheseothertechnologies?
Ourfirstresponseisthatwearenotarguingthateveryoneshould.Severalofthoseothertechnologiesarequitegoodandarereasonableoptionsinsomesituations.Inothersituations,however,JSPisclearlybetter.Hereareafewofthereasons.
2.1Versus.NETandActiveServerPages(ASP)
.NETiswell-designedtechnologyfromMicrosoft.ASP.NETisthepartthatdirectlycompeteswithservletsandJSP.TheadvantagesofJSParetwofold.First,JSPisportabletomultipleoperatingsystemsandWebservers;youaren'tlockedintodeployingonWindowsandIIS.Althoughthecore.NETplatformrunsonafewnon-Windowsplatforms,theASPpartdoesnot.YoucannotexpecttodeployseriousASP.NETapplicationsonmultipleserversandoperatingsystems.Forsomeapplications,thisdifferencedoesnotmatter.Forothers,itmattersgreatly.Second,forsomeapplicationsthechoiceoftheunderlyinglanguagemattersgreatly.Forexample,although.NET'sC#languageisverywelldesignedandissimilartoJava,fewerprogrammersarefamiliarwitheitherthecoreC#syntaxorthemanyauxiliarylibraries.Inaddition,manydevelopersstillusetheoriginalversionofASP.Withthisversion,JSPhasaclearadvantageforthedynamiccode.WithJSP,thedynamicpartiswritteninJava,notVBScriptoranotherASP-specificlanguage,soJSPismorepowerfulandbettersuitedtocomplexapplicationsthatrequirereusablecomponents.
YoucouldmakethesameargumentwhencomparingJSPtothepreviousversionofColdFusion;withJSPyoucanuseJavaforthe"realcode"andarenottiedtoaparticularserverproduct.However,thecurrentreleaseofColdFusioniswithinthecontextofaJ2EEserver,allowingdeveloperstoeasilymixColdFusionandservlet/JSPcode.
2.2VersusPHP
PHP(arecursiveacronymfor"PHP:
HypertextPreprocessor")isafree,open-source,HTML-embeddedscriptinglanguagethatissomewhatsimilartobothASPandJSP.OneadvantageofJSPisthatthedynamicpartiswritteninJava,whichalreadyhasanextensiveAPIfornetworking,databaseaccess,distributedobjects,andthelike,whereasPHPrequireslearninganentirelynew,lesswidelyusedlanguage.AsecondadvantageisthatJSPismuchmorewidelysupportedbytoolandservervendorsthanisPHP.
2.3VersusPureServlets
JSPdoesn'tprovideanycapabilitiesthatcouldn't,inprinciple,beaccomplishedwithservlets.Infact,JSPdocumentsareautomaticallytranslatedintoservletsbehindthescenes.Butitismoreconvenienttowrite(andtomodify!
)regularHTMLthantouseazillionprintlnstatementstogeneratetheHTML.Plus,byseparatingthepresentationfromthecontent,youcanputdifferentpeopleondifferenttasks:
yourWebpagedesignexpertscanbuildtheHTMLbyusingfamiliartoolsandeitherleaveplacesforyourservletprogrammerstoinsertthedynamiccontentorinvokethedynamiccontentindirectlybymeansofXMLtags.
DoesthismeanthatyoucanjustlearnJSPandforgetaboutservlets?
Absolutelynot!
JSPdevelopersneedtoknowservletsforfourreasons:
1.JSPpagesgettranslatedintoservlets.Youcan'tunderstandhowJSPworkswithoutunderstandingservlets.
2.JSPconsistsofstaticHTML,special-purposeJSPtags,andJavacode.WhatkindofJavacode?
Servletcode!
Youcan'twritethatcodeifyoudon'tunderstandservletprogramming.
3.SometasksarebetteraccomplishedbyservletsthanbyJSP.JSPisgoodatgeneratingpagesthatconsistoflargesectionsoffairlywellstructuredHTMLorothercharacterdata.Servletsarebetterforgeneratingbinarydata,buildingpageswithhighlyvariablestructure,andperformingtasks(suchasredirection)thatinvolvelittleornooutput.
4.SometasksarebetteraccomplishedbyacombinationofservletsandJSPthanbyeitherservletsorJSPalone.
2.4VersusJavaScript
JavaScript,whichiscompletelydistinctfromtheJavaprogramminglanguage,isnormallyusedtodynamicallygenerateHTMLontheclient,buildingpartsoftheWebpageasthebrowserloadsthedocument.ThisisausefulcapabilityanddoesnotnormallyoverlapwiththecapabilitiesofJSP(whichrunsonlyontheserver).JSPpagesstillincludeSCRIPTtagsforJavaScript,justasnormalHTMLpagesdo.Infact,JSPcanevenbeusedtodynamicallygeneratetheJavaScriptthatwillbesenttotheclient.So,JavaScriptisnotacompetingtechnology;itisacomplementaryone.
ItisalsopossibletouseJavaScriptontheserver,mostnotablyonSunONE(formerlyiPlanet),IIS,andBroadVisionservers.However,Javaismorepowerful,flexible,reliable,andportable.
2.5VersusWebMacroorVelocity
JSPisbynomeansperfect.Manypeoplehavepointedoutfeaturesthatcouldbeimproved.Thisisagoodthing,andoneoftheadvantagesofJSPisthatthespecificationiscontrolledbyacommunitythatdrawsfrommanydifferentcompanies.So,thetechnologycanincorporateimprovementsinsuccessivereleases.
However,somegroupshavedevelopedalternativeJava-basedtechnologiestotrytoaddressthesedeficiencies.This,inourjudgment,isamistake.Usingathird-partytoollikeApacheStrutsthataugmentsJSPandservlettechnologyisagoodideawhenthattooladdssufficientbenefittocompensatefortheadditionalcomplexity.ButusinganonstandardtoolthattriestoreplaceJSPisabadidea.Whenchoosingatechnology,youneedtoweighmanyfactors:
standardization,portability,integration,industrysupport,andtechnicalfeatures.TheargumentsforJSPalternativeshavefocusedalmostexclusivelyonthetechnicalfeaturespart.Butportability,standardization,andintegrationarealsoveryimportant.Forexample,theservletandJSPspecificationsdefineastandarddirectorystructureforWebapplicationsandprovidestandardfiles(.warfiles)fordeployingWebapplications.AllJSP-compatibleserversmustsupportthesestandards.FilterscanbesetuptoapplytoanynumberofservletsorJSPpages,butnottononstandardresources.ThesamegoesforWebapplicationsecuritysettings.
Besides,thetremendousindustrysupportforJSPandservlettechnologyresultsinimprovementsthatmitigatemanyofthecriticismsofJSP.Forexample,theJSPStandardTagLibraryandtheJSP2.0expressionlanguageaddresstwoofthemostwell-foundedcriti
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