JSP技术 ---外文文献.doc

苏州大学文正学院本科生毕业设计（论文）外文文献JSPTechnology andServletsJSP profileJSP(JavaServerPages)isinitiatedbySunMicrosystems,Inc.,withmanycompaniestoparticipateintheestablishmentofadynamicwebpagetechnicalstandards.JSPtechnologysomewhatsimilartoASPtechnology,itisinthetraditionalHTMLwebpagedocument(*.htm,*.html)toinserttheJavaprogrammingparagraph(Scriptlet)andJSPtag(tag),thusJSPdocuments(*.jsp).UsingJSPdevelopmentoftheWebapplicationiscrossthatcanrunonLinux,isalsoavailableforotheroperatingsystems.JSPtechnologytousetheJavaprogramminglanguagepreparedbythecategoryofXMLtagsandscriptlets,toproducedynamicpagespackageprocessinglogic.Pagealsovisitbytagsandscriptletsexistintheservicessideoftheresourcesoflogic.JSPpagelogicandwebpagedesignanddisplayseparation,supportreusablecomponent-baseddesign,Web-basedapplicationdevelopmentisrapidandeasy.WebserverinthefaceofvisitsJSPpagerequest,thefirstimplementationoftheproceduresof,andthentogetherwiththeresultsoftheimplementationofJSPdocumentsinHTMLcodewiththereturntothecustomer.InserttheJavaprogrammingoperationofthedatabasecanbereorientedwebsites,inordertoachievetheestablishmentofdynamicpagesneededtofunction.JSPandJavaServlet,isintheimplementationoftheserver,usuallyreturnedtotheclientisanHTMLtext,aslongastheclientbrowserwillbeabletovisit.JSP1.0specificationofthefinalversionislaunchedinSeptember1999,Decemberhasintroduced1.1specifications.AtpresentrelativelynewisJSP1.2norms,JSP2.0normsofthedrafthasalsobeenintroduced.JSPpagesfromHTMLcodeandJavacodeembeddedinoneofthecomponents.JSscriptlanguagesynopsisJSisjavascrip,JavascriptisonekindthescriptlanguagewhichcomesbytheNetscapeLiveScriptdevelopment,themainpurposeistosolvetheserverterminallanguage,forinstancePerl,carry-overspeedquestion.Atthattimeservedtheendtoneedtocarryontheconfirmationtothedata,becausethenetworkspeedwasquiteslow,onlythen28.8kbps,theconfirmationstepwastestimeweretoomany.ThereforeNetscapebrowserNavigatorhasjoinedJavascript,hasprovidedthedataconfirmationbasicfunction.TheJavaScriptofficialnameis“ECMAScript”.ThisstandardbyECMAorganizationdevelopmentandmaintenance.ECMA262istheofficialJavaScriptstandard.ThisstandardbasedonJavaScript(Netscape)andJScript(Microsoft).Netscape(Navigator2.0)BrendanEichhasinventedthislanguage,startedfrom1996,alreadyappearedinallNetscapeandintheMicrosoftbrowser.TheECMA262developmentbeganin1996,in1997July,theECMAgeneralmeetinghasaccepteditsfirstedition.Thescriptusesonespecificdescriptivelanguage,restsoncertainformcompilationtobepossibletheexecutiondocument,isalsocalledasgreatorthebatchrundocument.Thescriptusuallymaytransfertemporarilybytheapplicationprocedureandcarryout.Eachkindofscriptpresentwidelyisappliedinthehomepagedesign,becausethescriptnotonlymayreducethehomepagethescaleandraisesthehomepagebrowsingspeed,moreovermayenrichthehomepageperformance,likeanimation,soundandsoon.Citesamostcommonexample,whenweclickinthehomepagetheEmailaddresscantransferOutlookExpressortheFoxmailthiskindofmailsoftwareautomatically,isrealizesthroughthescriptfunction.Alsobecauseofscriptthesecharacteristics,thehumanwhoharborsulteriormotivesbysomeareoftenusing.Forexamplejoinssomedestructioncomputersystemsorderinthescript,likethisworksastheuserbrowsinghomepage,oncetransfersthiskindofscript,willthencausetheuserthesystemtocomeundertheattack.Thereforetheusershouldactaccordingtovisitshomepagethetrustdegreeselectivesecurityrank,speciallyregardingtheseitselfcontentontheillegalhomepage,donotpermittheusescripteasily.Through“thesafeestablishment”thedialogbox,thechoice“thescript”underoptioneachkindofestablishmentmaywitheaserealizetoscriptbeingforbidandbeginsusing.JSPandServletsThetechnologyofJSPandServletisthemostimportanttechnologywhichuseJavatechnologytoexploitrequestofserver,anditisalsothestandardwhichexploitbusinessapplication.Javadevelopersprefertouseitforavarietyofreasons,oneofwhichisalreadyfamiliarwiththeJavalanguageforthedevelopmentofthistechnologyareeasytolearnJavatotheotherisapreparation,runeverywheretobringtheconceptofWebapplications,Toachieveaone-preparedeverywhererealized.Andmoreimportantly,iffollowedsomeoftheprinciplesofgooddesign,itcanbesaidofseparatingandcontenttocreatehigh-quality,reusable,easytomaintainandmodifytheapplication.Forexample,ifthedocumentinHTMLembeddedJavacodetoomuch(script),willleadthedevelopedapplicationisextremelycomplex,difficulttoread,itisnoteasyreuse,butalsoforfuturemaintenanceandmodificationwillalsocausedifficulties.Infact,CSDNtheJSP/Servletforum,canoftenseesomequestions,thecodeisverylong,canlogicisnotveryclear,alargenumberofHTMLandJavacodemixedtogether.Thisistherandomdevelopmentofthedefects.EarlydynamicpagesmainlyCGI(CommonGatewayInterface,publicGatewayInterface)technology,youcanusedifferentlanguagesoftheCGIprograms,suchasVB,C/C+orDelphi,andsoon.ThoughthetechnologyofCGIisdevelopedandpowerful,becauseofdifficultiesinprogramming,andlowefficiency,modifycomplexshortcomings,itisgraduallybeingreplacedbythetrend.Ofallthenewtechnology,JSP/Servletwithmoreefficientandeasytoprogram,morepowerful,moresecureandhasagoodportability,theyhavebeenmanypeoplebelievethatthefutureisthemostdynamicsiteofthefuturedevelopmentoftechnology.SimilartoCGI,Servletsupportrequest/responsemodel.Whenacustomersubmitarequesttotheserver,theserverpresentedtherequestServlet,Servletresponsibleforhandlingrequestsandgeneratearesponse,andthengavetheserver,andthenfromtheserversenttothecustomer.AndtheCGIisdifferent,Servletnotgenerateanewprocess,butwithHTTPServeratthesameprocess.Itthreadsthroughtheuseoftechnology,reducetheservercosts.Servlethandlingoftherequestprocessisthis:Whenreceivedfromtheclientsrequest,callingservicemethods,themethodofServletarrivalofthefirstjudgementiswhattypeofrequest(GET/POST/HEAD),thencallstheappropriatetreatment(DoGet/doPost/doHead)andgeneratearesponse.Althoughsuchacomplex,infact,simplysaidtoServletisaJavaclass.AndthegeneralcategoryofthedifferenceisthatthistypeoperatinginaServletcontainer,whichcanprovidesessionmanagementandtargetedlifecyclemanagement.SothatwhenyouusetheServlet,youcangetallthebenefitsoftheJavaplatform,includingthesafetyofthemanagement,useJDBCaccessthedatabaseandcrossplatformcapability.Moreover,Servletusingthread,andcandevelopmoreefficientWebapplications.JSPtechnologyisakeyJ2EEtechnology,itatahigherlevelofabstractionofaServlet.ItallowsconventionalstaticanddynamicHTMLcontentgeneratedbycombininganHTMLpagelookslike,butasaServlettorun.TherearemanycommercialapplicationserversupportJSPtechnology,suchasBEAWebLogic,IBMWebSphere,JRun,andsoon.JSPandServletusemorethansimple.IfyouhaveaJSPsupportforWebservers,andaJSPdocument,youcanputitFangdaoanystaticHTMLfilescanbeplaced,donothavetocompile,donothavetopack,donothavetoClassPathsettings,youcanvisitasordinaryWebItdidvisit,theserverwillautomaticallyhelpyoutodootherwork.JSPdocumentlookslikeanordinarystaticHTMLdocument,butinsidecontainsanumberofJavacode.Ituses.Jspthesuffix,usedtotelltheserverthisdocumentinneedofspecialtreatment.WhenwevisitaJSPpage,thedocumentwillfirstbetranslatedintoaJSPengineJavasourcefiles,isactuallyaServlet,andcompiler,andthen,likeotherServlet,fromServletenginetohandle.Servletengineofthistypeloading,handlingrequestsfromcustomers,andtheresultsreturnedtothecustomer.Afteranothervisitthispagetothecustomer,aslongasthepapertherehavebeennochanges,JSPenginehasbeenloadeddirectlycalltheServlet.Ifyouhavealreadybeenmodified,itwillbeonceagaintheimplementationoftheaboveprocess,translate,compileandload.Infact,thisistheso-calledfirstpersontopunishment.Becausewhenthefirstvisittotheimplementationofaseriesoftheaboveprocess,sowillspendsometimeaftersuchavisitwouldnot.JavaservletsofferapowerfulAPIthatprovidesaccesstoalltheinformationabouttherequest,thesession,biningJSPwithservletsletsyouclearlyseparatetheapplicationlogicfromthepresentationoftheapplication;inotherwords,itletsyouusethemostappropriatecomponenttypefortherolesofModel,ViewandController.Servlets,Filters,andListenersAservletisaJavaclassthatextendsaserverwithfunctionalityforprocessingarequestandproducingaresponse.ItsimplementedusingtheclassesandinterfacesdefinedbytheServletAPI.TheAPIconsistsoftwopackages:thejavax.servletpackagecontainsclassesandinterfacesthatareprotocolindependent,whilethejavax.servlet.httppackageprovidesHTTP-specificextensionsandutilityclasses.Whatmakesaservletaservletisthattheclassimplementsaninterfacenamedjavax.servlet.Servlet,eitherdirectlyorbyextendingoneofthesupportclasses.Thisinterfacedefinesthemethodsusedbythewebcontainertomanageandinteractwiththe servlet.AservletforprocessingHTTPrequeststypicallyextendsthejavax.servlet.http.HttpServletclass.ThisclassimplementstheServletinterfaceandprovidesadditionalmethodssuitableforHTTPprocessing.ServletLifecycleThewebcontainermanagesallaspectsoftheservletslifecycle.Itcreatesaninstanceoftheservletclasswhenneeded,passesrequeststotheinstanceforprocessing,andeventuallyremovestheinstance.ForanHttpServlet,thecontainercallsthefollowingmethodsattheappropriatetimesintheservletlifecycle.BesidesthedoGet()anddoPost()methods,therearemethodscorrespondingtotheotherHTTPmethods:doDelete(),doHead(),doOptions(),doPut(),anddoTrace().Typicallyyoudontimplementthesemethods;theHttpServletclassalreadytakescareofHEAD,OPTIONS,andTRACErequestsinawaythatssuitableformostservlets,andtheDELETEandPUTHTTPmethodsarerarelyusedinawebapplication.Itsimportanttorealizethatthecontainercreatesonlyoneinstanceofeachservlet.Thismeansthattheservletmustbethreadsafe-abletohandlemultiplerequestsatthesametime,eachexecutingasaseparatethreadthroughtheservletcode.Withoutgettinglostindetails,yousatisfythisrequirementwithregardstoinstancevariablesifyoumodifythereferencedobjectsonlyintheinit()anddestroy()methods,andjustreadthemintherequestprocessingmethods.CompilingandInstallingaServletTocompileaservlet,youmustfirstensurethatyouhavetheJARfilecontainingallServletAPIclassesintheCLASSPATHenvironmentvariable.TheJARfileisdistributedwithallwebcontainers.Tomcatincludesitinafilecalledservlet.jar,locatedinthecommon/libdirectory.OnaWindowsplatform,youincludetheJARfileintheCLASSPATH.ReadingaRequestOneoftheargumentspassedtothedoGet()anddoPost()methodsisanobjectthatimplementstheHttpServletRequestinterface.Thisinterfacedefinesmethodsthatprovideaccesstoawealthofinformationabouttherequest.GeneratingaResponseBesidestherequestobject,thecontainerpassesanobjectthatimplementstheHttpServletResponseinterfaceasanargumenttothedoGet()anddoPost()methods.Thisinterfacedefinesmethodsforgettingawriterorstreamfortheresponsebody.Italsodefinesmethodsforsettingtheresponsestatuscodeandheaders.UsingFiltersandListenersTheservletspecificationdefinestwocomponenttypesbesideservlets:filtersandlisteners.ThesetwotypeswereintroducedintheServlet2.3specification,soifyoureusingacontainerthatdoesntyetsupportthisversionofthespecification,Imafraidyoure outofluck.FiltersAfilterisacomponentthatcaninterceptarequesttargetedforaservlet,JSPpage,orstaticpage,aswellastheresponsebeforeitssenttotheclient.Thismakesiteasytocentralizetasksthatapplytoallrequests,suchasaccesscontrol,logging,andchargingforthecontentortheservicesofferedbytheapplication.Afilterhasfullaccesstothebodyandheadersoftherequestandresponse,soitcanalsoperformvarioustransformations.Oneexampleiscompressingtheresponsebodyifthe Acceptlanguagerequestheaderindicatesthattheclientcanhandleacompressedresponse.AfiltercanbeappliedtoeitheraspecificservletortoallrequestsmatchingaURLpattern,suchasURLsstartingwiththesamepathelementsorhavingthesameextension.ListenersListenersallowyourapplicationtoreacttocertainevents.PriortoServlet2.3,youcouldhandleonlysessionattributebindingevents(triggeredwhenanobjectwasaddedorremovedfromasession).Youcoulddothisbylettingtheobjectsavedasasessionattributimplementthe HttpSessionBindingListenerinterface.Withthenewinterfacesintroducedinthe2.3versionofthespecification,youcancreatelistenersforservletcontextandsessionlifecycleeventsaswellassessionactivationandpassivationevents(usedbyacontainerthattemporarilysavessessionstatetodiskormigratesasessiontoanotherserver).Anewsessionattributeeventlisteneralsomakesitpossibletodealwithattributebindingeventsforallsessionsinoneplace,insteadofplacingindividuallistenerobjectsineachsession.ThenewtypesoflistenersfollowthestandardJavaeventmodel.Inotherwords,alistenerisaclassthatimplementsoneormoreofthelistenerinterfaces.Theinterfacesdefinemethodsthatcorrespondtoevents.Thelistenerclassisregisteredwiththecontainerwhentheapplicationstarts,andthecontainerthencallstheeventmethodsattheappropriatetimes.InitializingSharedResourcesUsingaListenerBeanslikethistypicallyneedtobeinitializedbeforetheycanbeused.Forinstance,theymayneedareferencetoadatabaseorsomeotherexternaldatasourceandmaycreateaninitialinformationcacheinmemorytoprovidefastaccesseventothefirstrequestfordata.YoucanincludecodeforinitializationofthesharedresourcesintheservletandJSPpagesthatneedthem,butamoremodularapproachistoplaceallthiscodeinoneplaceandlettheotherpartsoftheapplicationworkontheassumptionthattheresourcesarealreadyinitializedandavailable.Anapplicationlifecyclelistenerisaperfecttoolforthistypeofresourceinitialization.Thistypeoflistenerimplementsthejavax.servlet.ServletContextListenerinterface,withmethodscalledbythecontainerwhentheapplicationstartsandwhenitshutsdown.PickingtheRightComponentTypeforEachTaskTheProjectBillboardapplicationintroducedisafairlycomplexapplication.Halfthepagesarepurecontrollerandbusinesslogicprocessing,itaccessesadatabasetoauthenticateusers,andmostpagesrequireaccesscontrol.Inreallife,itwouldlikelycontainevenmorepages,forinstance,pagesforaccesstoashareddocumentarchive,timeschedules,andasetofpagesforadministration.Astheapplicationevolves,itmaybecomehardtomaintainasapureJSPapplication.Itseasytoforgettoincludetheaccesscontrolcodeinnewpages.ThisisclearlyanapplicationthatcanbenefitfromusingacombinationofJSPpagesandthecomponenttypesdefinedbytheservletspecificationfortheMVCroles.Letslookatthemainrequirementsandseehowwecanmapthemtoappropriatecomponenttypes:Databaseaccessshouldbeabstracted,toavoidknowledgeofaspecificdataschemaordatabaseengineinmorethanonepartoftheapplication:beansintheroleofModelcanbeusedtoaccomplishthis.Thedatabaseaccessbeansmustbemadeavailabletoallotherpartsoftheapplicationwhenitstarts:anap