外文翻译-JSP的技术发展历史 (2)

外文原文THETECHNIQUEDEVELOPMENTHISTORYOFJSPBy:KathySierraandBertBatesSource:Servlet&JSPTheJavaServerPages(JSP)isakindofaccordingtowebofthescriptplaitdistancetechnique,similarcarriesthescriptlanguageofJavaintheserveroftheNetscapecompanyofserver-sideJavaScript(SSJS)andtheActiveServerPages(ASP)oftheMicrosoft.JSPcomparestheSSJSandASPtohavebettercanexpandsex,anditisnomoreexclusivethananyfactoryorsomeoneparticularserverofWeb.ThoughthenormofJSPistobedrawupbytheSuncompanyof,anyfactorycancarryouttheJSPonownsystem.TheAfterSunreleasetheJSP(theJavaServerPages)formally,thethiskindofnewWebapplicationdevelopmenttechniqueveryquicklycausedthepeoplesconcern.JSPprovidedaspecialdevelopmentenvironmentfortheWebapplicationthatestablishesthehighdynamicstate.AccordingtotheSunparlance,theJSPcanadapttoincludetheApacheWebServer,IIS4.0onthemarketatinsideof85%serverproduct.ThischapterwillintroducetherelatedknowledgeofJSPandDatabases,andJavaBeanrelatedcontents,isallcertainlyrougherintroductionamongthembasiccontents,sayperhapstoisaGuideonly,ifthereaderneedsthemoredetailedinformation,pleasingthebookofconsultthehomologousJSP.1.1GENERALIZETheJSP(JavaServerPages)isfromthecompanyofSunMicrosystemsinitiate,themanycompaniestheparticipatetothebuildupthetogetheroftheakindtheofdynamicthestatewebthepagetechniquestandard,theithavetheitintheconstructiontheofthedynamicstatethewebpagethestrongbutthedonottheespeciallyofthefunction.JSPandthetechniqueofASPoftheMicrosoftisveryalike.BothallprovidetheabilitythatmixeswithacertainprocedurecodeandisexplainbythelanguageenginetocarryouttheprocedurecodeinthecodeofHTML.Underneathwearesimpleofcarryontheintroductiontoit.JSPpagesaretranslatedintoservlets.So,fundamentally,anytaskJSPpagescanperformcouldalsobeaccomplishedbyservlets.However,thisunderlyingequivalencedoesnotmeanthatservletsandJSPpagesareequallyappropriateinallscenarios.Theissueisnotthepowerofthetechnology,itistheconvenience,productivity,andmaintainabilityofoneortheother.Afterall,anythingyoucandoonaparticularcomputerplatformintheJavaprogramminglanguageyoucouldalsodoinassemblylanguage.Butitstillmatterswhichyouchoose.JSPprovidesthefollowingbenefitsoverservletsalone:1）ItiseasiertowriteandmaintaintheHTML.YourstaticcodeisordinaryHTML:noextrabackslashes,nodoublequotes,andnolurkingJavasyntax.2）YoucanusestandardWeb-sitedevelopmenttools.EvenHTMLtoolsthatknownothingaboutJSPcanbeusedbecausetheysimplyignoretheJSPtags.3）Youcandivideupyourdevelopmentteam.TheJavaprogrammerscanworkonthedynamiccode.TheWebdeveloperscanconcentrateonthepresentationlayer.Onlargeprojects,thisdivisionisveryimportant.Dependingonthesizeofyourteamandthecomplexityofyourproject,youcanenforceaweakerorstrongerseparationbetweenthestaticHTMLandthedynamiccontent.Now,thisdiscussionisnottosaythatyoushouldstopusingservletsanduseonlyJSPinstead.Bynomeans.Almostallprojectswilluseboth.Forsomerequestsinyourproject,youwilluseservlets.Forothers,youwilluseJSP.Forstillothers,youwillcombinethemwiththeMVCarchitecture.Youwanttheappropriatetoolforthejob,andservlets,bythemselves,donotcompleteyourtoolkit.1.2SOURCEOFJSPThetechniqueofJSPofthecompanyofSun,makingthepageofWebdevelopthepersonnelcanusetheHTMLperhapsmarkingofXMLtodesigntoturntheendpagewithformat.UsetheperhapssmallscriptfuturelifeofmarkingofJSPbecomesthedynamicstateonthepagecontents.(thecontentschangesaccordingtotheclaimof)TheJavaServletisatechnicalfoundationofJSP,andthelargeWebappliesthedevelopmentoftheproceduretoneedtheJavaServlettomatchwithwiththeJSPandthencancomplete,thisnameofServletcomesfromtheApplet,thelocaltranslationmethodofnowisalotof,thisbookinordernottomisconstruction,decidethedirectadoptionServletbutdontdoanytranslation,ifreaderwouldliketo,cancallitassmallserviceprocedure.TheServletissimilartotraditionalCGI,ISAPI,NSAPIetc.Webproceduredevelopmentthefunctionofthetoolinfact,atusetheJavaServlethereafter,thecustomerneednotuseagainthelowlymethodofCGIofefficiency,alsoneednotuseonlytheabilitycometobornpageofWebofdynamicstateinthemethodofAPIthatacertainfixedWebserverterracecirculate.ManyserversofWeballsupporttheServlet,evennotsupporttheServletserverofWebdirectlyandcanalsopasstheadditionalappliedserverandthemoldpiecestosupporttheServlet.ReceivebenefitinthecharacteristicoftheJavacross-platform,theServletisalsoaterraceirrelevant,actually,aslongasmatchthenormofJavaServlet,theServletiscompletetohavenothingtodowithterraceandistohavenothingtodowithserverofWeb.BecausetheJavaServletisinternaltoprovidetheservicebythelinedistance,neednotstartaprogresstotheeachclaimses,andmakeuseofthemulti-threadingmechanismcanatthesametimeforseveralclaimservice,thereforetheefficiencyofJavaServletisveryhigh.ButtheJavaServletalsoisnottohasnoweakness,similartotraditionalCGI,ISAPI,theNSAPImethod,theJavaServletistomakeuseoftooutputtheHTMLlanguagesentencetocarryoutthedynamicstatewebpageof,ifdevelopthewholewebsitewiththeJavaServlet,theintegrationprocessofthedynamicstatepartandthestaticstatepageisanevil-forebodingdreamsimply.ForsolvingthiskindofweaknessoftheJavaServlet,theSUNreleasedtheJSP.Anumberofyearsago,Martywasinvitedtoattendasmall20-personindustryroundtablediscussiononsoftwaretechnology.SittingintheseatnexttoMartywasJamesGosling,inventoroftheJavaprogramminglanguage.Sittingseveralseatsawaywasahigh-levelmanagerfromaverylargesoftwarecompanyinRedmond,Washington.Duringthediscussion,themoderatorbroughtupthesubjectofJini,whichatthattimewasanewJavatechnology.Themoderatoraskedthemanagerwhathethoughtofit,andthemanagerrespondedthatitwastooearlytotell,butthatitseemedtobeanexcellentidea.Hewentontosaythattheywouldkeepaneyeonit,andifitseemedtobecatchingon,theywouldfollowhiscompanysusualembraceandextendstrategy.Atthispoint,GoslinglightheartedlyinterjectedYoumeandisgraceanddistend.Now,thegrievancethatGoslingwasairingwasthathefeltthatthiscompanywouldtaketechnologyfromothercompaniesandsubornitfortheirownpurposes.Butguesswhat?Theshoeisontheotherfoothere.TheJavacommunitydidnotinventtheideaofdesigningpagesasamixtureofstaticHTMLanddynamiccodemarkedwithspecialtags.Forexample,ColdFusiondidityearsearlier.EvenASP(aproductfromtheverysoftwarecompanyoftheaforementionedmanager)popularizedthisapproachbeforeJSPcamealonganddecidedtojumponthebandwagon.Infact,JSPnotonlyadoptedthegeneralidea,itevenusedmanyofthesamespecialtagsasASPdid.TheJSPisanestablishmentatthemodelofJavaservletsonoftheexpressionlayertechnique,itmakestheplaitwritetheHTMLtobecomemoresimple.BeliketheSSJS,italsoallowsyoucarrythestaticstateHTMLcontentsandserversthescriptmixtoputtogethertheborndynamicstateexportation.JSPthescriptlanguagethattheJavaisthetacitapproval,however,beliketheASPandcanuseotherlanguages(suchasJavaScriptandVBScript),thenormofJSPalsoallowstouseotherlanguages.1.3JSPCHARACTERISTICSIsaserviceaccordingtothescriptlanguageinsomeonelanguageofthestaturessystemthiskindofdiscuss,theJSPshouldbeseemakeisakindofscriptlanguage.However,beakindofscriptlanguage,theJSPseemedtobetoostrongagain,almostcanuseallJavasintheJSP.Beakindofaccordingtotextoriginallyof,takemanifestationasthecentraldevelopmenttechnique,theJSPprovidedalladvantagesoftheJavaServlet,and,whencombinewithaJavaBeanstogether,providingakindofmakecontentsandmanifestationthatsimplewaythatlogicseparate.Separatethecontentsandadvantageoflogicalmanifestationsis,thepersonnelwhorenewsthepageexternalappearanceneednotknowthecodeofJava,andrenewtheJavaBeanspersonnelalsoneednotbedesignthewebpageofexpertinhand,canusetotakethepageofJavaBeansJSPtodefinethetemplateofWeb,tobuildupafromhavethealikeexternalappearanceofthewebsitethatpageconstitute.JavaBeanscompletesthedatatoprovide,havingnocodeofJavainthetemplatethus,thismeansthatthesetemplatescanbewrittenthepersonnelbyaHTMLplaittosupport.Certainly,canalsomakeuseoftheJavaServlettocontrolthelogicofthewebsite,adjustthroughtheJavaServlettousethewayofthedocumentofJSPtoseparatewebsiteoflogicandcontents.Generallyspeaking,inactualengineofJSP,thepageofJSPistheeditandtranslatetypewhilecarryout,notexplainthetypeof.Explainthedynamicstatewebpagedevelopmenttoolofthetype,suchasASP,PHP3etc.,becausespeedetc.reason,havealreadycantsatisfycurrentthelargeelectroniccommerceneedsappliedly,traditionaldevelopmenttechniquesareallattoeditandtranslatetheexecutivewaychange,suchastheASPASP+;PHP3PHP4.IntheJSPnormbook,didnotrequesttheprocedureintheJSPcodepart(becalledtheScriptlet)andmustwritewiththeJavadefinitely.Actually,havesomeenginesofJSPareadoptiveotherscriptlanguagessuchastheEMAC-Script,etc.,butactuallythisafewscriptlanguagesalsoaretosetupontheJava,editandtranslatefortheServlettocarryoutof.WriteaccordingtothenormofJSP,havenoScriptletofrelationwithJavaalsoiscanof,however,mainlylieintheabilityandJavaBeans,theEnterpriseJavaBeansesbecauseoftheJSPstrongfunctiontoworktogether,soevenistheScriptletpartnottousetheJava,editandtranslateofperformancecodealsoshouldisrelatedwithJava.1.4JSPMECHANISMTocomprehendtheJSPhowunitethetechnicaladvantagethatabovevariousspeakof,cometocarryoutvariousresulteasily,thecustomermustunderstandthedifferentiationofthemoduledevelopsforthewebpageofthecenterandthepagedevelopsforthewebpageofthecenterfirst.TheSSJSandASPareallinseveralyearagotorelease,thenetworkofthattimeisstillveryyoung,nooneknowstostillhaveinadditiontomakingallbusiness,datasandtheexpressionlogicentertheoriginalwebpageentirelyheapwhatbettersolvethemethod.Thiskindofmodelthattakepageasthecenterstudiesandgetstheveryfastdevelopmenteasily.However,alongwithchangeoftime,thepeopleknowthatthiskindofmethodisunwellinsetuplarge,theWebthatcanupgradeappliestheprocedure.Theexpressionlogicwriteinthescriptenvironmentwaslockinthepage,onlypassingtosheartosliceandgluetostickthencandriveheavyuse.Expressthelogictousuallymixtogetherwithbusinessandthedatalogics,whenthismakesbetheproceduremembertotrytochangeanexternalappearancethatappliestheprocedurebutdonotwanttobreakwithitslliedbusinesslogic,applytheprocedureofmaintenancebeliketowalkthesimilardifficultyontheeggshell.Infactinthebusinessenterprise,heavyusetheapplicationofthemodulealreadythroughverymature,noonewouldliketorewritethoselogicsfortheirappliedprocedure.HTMLandsketchthedesignerhandedovertotheimplementworkoftheirdesigntheWebplaittheonewhowrite,maketheyhavetodoublework-Usuallyisthehandicraftplaittowrite,becausehavenofittoolandcancarrythescriptandtheHTMLcontentsknottotheservertoputtogether.Chienbutspeech,applythecomplexityoftheprocedurealongwiththeWebtopromotecontinuously,thedevelopmentmethodthattakepageasthecenterlimitssextobecometogetupobviously.Atthesametime,thepeoplealwaysatlookforthebettermethodofbuilduptheWebapplicationprocedure,themodulespreadsincustomersmachine/servertherealm.JavaBeansandActiveXwerepublishedthecompanytoexpandtoapplytheproceduredeveloperforJavaandWindowstousetocometodevelopthecomplicatedprocedurequicklybythefastapplicationproceduredevelopment(RAD)tool.Thesetechniquesmaketheexpertinthesomerealmbeabletowritethemodulefortheperpendicularapplicationplaitintheskillarea,butthedevelopercangofetchtheusagedirectlybutneednotcontroltheexpertiseofthisrealm.Beakindoftakemoduleasthecentraldevelopmentterrace,theJSPappeared.ItwiththeJavaBeansandEnterpriseJavaBeans(EJB)moduleincludesthemodelofthebusinessandthedatalogicforfoundation,provideagreatdealoflabelandascriptterracestousetocometoshowintheHTMLpagefromthecontentsofJavaBeanscreationorsendapresentinreturn.BecauseofthepropertythatregardsthemoduleasthecenteroftheJSP,itcandriveJavaandnotthedeveloperofJavausesequally.NotthedeveloperofJavacanpasstheJSPlabel(Tags)tousetheJavaBeansthatthedeluxedeveloperofJavaestablish.ThedeveloperofJavanotonlycanestablishandusetheJavaBeans,butalsocanusethelanguageofJavatocometocontrolmoreaccuratelyintheJSPpageaccordingtotheexpressionlogicofthefirstfloorJavaBeans.SeenowhowJSPishandleclaimofHTTP.Inbasicclaimmodel,aclaimdirectlywassendtoJSPpagein.ThecodeofJSPcontrolstocarryonhourofthelogicprocessingandmoduleofJavaBeanseshandoverwitheachother,andthemanifestationresultindynamicstatebornly,mixingwiththeHTMLpageofthestaticstateHTMLcode.TheBeanscanbeJavaBeansormoduleofEJBs.Moreover,themorecomplicatedclaimmodelcanseemakefromisrequestotherJSPpagesofthepagecallsignorJavaServlets.TheengineofJSPwantstochasethecodeofJavathatthelabelofJSP,codeofJavaintheJSPpageevenallconvertsintothebigpiecetogetherwiththestaticstateHTMLcontentsactually.ThesecodespiecewasorganizedtheJavaServletthatcustomercannotseetogotobytheengineofJSP,thentheServleteditsandtranslatethemautomaticallybytecodeofJava.Thus,thevisitantthatisthewebsiterequestsaJSPpage,undertheconditionofitisnotknowing,analreadyborn,theServletactualfullgeneralthatpreparedtoeditandtranslatecompletesallworks,veryconcealmentbutagainandefficiently.TheServletistoeditandtranslateof,sothecodeofJSPinthewebpagedoesnotneedwhentheeverytimerequeststhatpageisexplain.TheengineofJSPneedtobeeditandtranslateafterServletthecodeendismodifyonlyonce,thenthisServletthatedittedandtranslatecanbecarryout.TheinviewofthefactJSPengineautoisborntoeditandtranslatetheServletalso,neednotprocedurememberbeginstoeditandtranslatethecode,sotheJSPcanbringvividsexthatfunctionandfastdevelopmentsneedthatyouareefficiently.ComparedwiththetraditionalCGI,theJSPhastheequaladvantage.First,onthespeed,thetraditionalprocedureofCGIneedstousethestandardimportationofthesystemtooutputtheequipmentstocarryoutthedynamicstatewebpageborn,buttheJSPisdirectismutuallytheconnectionwithserver.AndsayfortheCGI,eachinterviewneedstoaddtoaddaprogresstohandle,theprogressbuildupanddestroybyburningconstantlyandwillbeanotsmallburdenforcalculatorofbetheserverofWeb.Thenextinorder,theJSPisspecializedtodevelopbutdesignfortheWebof,itspurposeisforbuildingupaccordingtotheWebappliedprocedure,includedthenormandthetoolofathewholeset.UsethetechniqueofJSPcancombinealotofJSPpagestobecomeaWebapplicationprocedureveryexpediently.2.1FRAMEWORKSAframeworkisareusable,semi-completeapplicationthatcanbespecializedtoproducecustomapplicationsJohnson.Likepeople,softwareapplicationsaremorealikethantheyaredifferent.Theyrunonthesamecomputers,expectinputfromthesamedevices,outputtothesamedisplays,andsavedatatothesameharddisks.Developersworkingonconventionaldesktopapplicationsareaccustomedtotoolkitsanddevelopmentenvironmentsthatleveragethesamenessbetweenapplications.Applicationframeworksbuildonthiscommongroundtoprovidedeveloperswithareusablestructurethatcanserveasthefoundationfortheirownproducts.Aframeworkprovidesdeveloperswithasetofbackbonecomponentsthathavethefollowingcharacteristics:1.Theyareknowntoworkwellinotherapplications.2.Theyarereadytousewiththenextproject.3.Theycanalsobeusedbyotherteamsintheorganization.Frameworksaretheclassicbuild-versus-buyproposition.Ifyoubuildit,youwillunderstanditwhenyouaredonebuthowlongwillitbebeforeyoucanrollyourown?Ifyoubuyit,youwillhavetoclimbthelearningcurveandhowlongisthatgoingtotake?Thereisnorightanswerhere,butmostobserverswouldagreethatframeworkssuchasStrutsprovideasignificantreturnoninvestmentcomparedtostartingfromscratch,especiallyforlargerprojects.2.2OTHERTYPESOFFRAMEWORKSTheideaofaframeworkappliesnotonlytoapplicationsbuttoapplicationcomponentsaswell.Throughoutthisarticle,weintroduceothertypesofframeworksthatyoucanusewithStruts.TheseincludetheLucenesearchengine,theScaffoldtoolkit,theStrutsvalidator,andtheTilestaglibrary.Likeapplicationframeworks,thesetoolsprovidesemi-completeversionsofasubsystemthatcanbespecializedtoprovideacustomcomponent.Someframeworkshavebeenlinkedtoaproprietarydevelopmentenvironment.ThisisnotthecasewithStrutsoranyoftheotherframeworksshowninthisbook.YoucanuseanydevelopmentenvironmentwithStruts:VisualAgeforJava,JBuilder,Eclipse,Emacs,andTextpadareallpopularchoicesamongStrutsdevelopers.IfyoucanuseitwithJava,youcanuseitwithStruts.2.3ENABLINGTECHNOLOGIESApplicationsdevelopedwithStrutsarebasedonanumberofenablingtechnologies.ThesecomponentsarenotspecifictoStrutsandunderlieeveryJavawebapplication.AreasonthatdevelopersuseframeworkslikeStrutsistohidethenastydetailsbehindacronymslikeHTTP,CGI,andJSP.AsaStrutsdeveloper,youdontneedtobeanalphabetsoupguru,butaworkingknowledgeofthesebasetechnologiescanhelpyoudevisecreativesolutionstotrickyproblems.2.4HYPERTEXTTRANSFERPROTOCOL(HTTP)Whenmediatingtalksbetweennations,diplomatsoftenfollowaformalprotocol.Diplomaticprotocolsaredesignedtoavoidmisunderstandingsandtokeepnegotiationsfrombreakingdown.Inasimilarvein,whencomputersneedtotalk,theyalsofollowaformalprotocol.Theprotocoldefineshowdataistransmittedandhowtodecodeitonceitarrives.WebapplicationsusetheHypertextTransferProtocol(HTTP)tomovedatabetweenthebrowserrunningonyourcomputerandtheapplicationrunningontheserver.ManyserverapplicationscommunicateusingprotocolsotherthanHTTP.Someofthesemaintainanongoingconnectionbetweenthecomputers.Theapplicationserverknowsexactlywhoisconnectedatalltimesandcantellwhenaconnectionisdropped.Becausetheyknowthestateofeachconnectionandtheidentityofeachpersonusingit,theseareknownasstatefulprotocols.Bycontrast,HTTPisknownasastatelessprotocol.AnHTTPserverwillacceptanyrequestfromanyclientandwillalwaysprovidesometypeofresponse,eveniftheresponseisjusttosayno.Withouttheoverheadofnegotiatingandretainingaconnection,statelessprotocolscanhandlealargevolumeofrequests.ThisisonereasonwhytheInternethasbeenabletoscaletomillionsofcomputers.AnotherreasonHTTPhasbecometheuniversalstandardisitssimplicity.AnHTTPrequestlookslikeanordinarytextdocument.ThishasmadeiteasyforapplicationstomakeHTTPrequests.YoucanevensendanHTTPrequestbyhandusingastandardutilitysuchasTelnet.WhentheHTTPresponsecomesback,itisalsoinplaintextthatdeveloperscanread.ThefirstlineintheHTTPrequestcontainsthemethod,followedbythelocationoftherequestedresourceandtheversionofHTTP.ZeroormoreHTTPrequestheadersfollowtheinitialline.TheHTTPheadersprovideadditionalinformationtotheserver.Thiscanincludethebrowsertypeandversion,acceptabledocumenttypes,andthebrowserscookies,justtonameafew.Ofthesevenrequestmethods,GETandPOSTarebyfarthemostpopular.Oncetheserverhasreceivedandservicedtherequest,itwillissueanHTTPresponse.ThefirstlineintheresponseiscalledthestatuslineandcarriestheHTTPprotocolversion,anumericstatus,andabriefdescriptionofthestatus.Followingthestatus