jsp技术概述与应用框架外文翻译Word下载.doc
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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-foundedcriticisms:
thelackofgooditer
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