JSP技术---外文文献(同名2250)(共11页)

1、实用文档外文文献JSPTechnology andServletsJSP profileJSP(JavaServerPages)isinitiatedbySunMicrosystems,Inc.,withmanycompaniestoparticipateintheestablishmentofadynamicwebpagetechnicalstandards.JSPtechnologysomewhatsimilartoASPtechnology,itisinthetraditionalHTMLwebpagedocument(*.htm,*.html)toinserttheJavaprogra

2、mmingparagraph(Scriptlet)andJSPtag(tag),thusJSPdocuments(*.jsp).UsingJSPdevelopmentoftheWebapplicationiscrossthatcanrunonLinux,isalsoavailableforotheroperatingsystems.JSPtechnologytousetheJavaprogramminglanguagepreparedbythecategoryofXMLtagsandscriptlets,toproducedynamicpagespackageprocessinglogic.P

3、agealsovisitbytagsandscriptletsexistintheservicessideoftheresourcesoflogic.JSPpagelogicandwebpagedesignanddisplayseparation,supportreusablecomponent-baseddesign,Web-basedapplicationdevelopmentisrapidandeasy.WebserverinthefaceofvisitsJSPpagerequest,thefirstimplementationoftheproceduresof,andthentoget

4、herwiththeresultsoftheimplementationofJSPdocumentsinHTMLcodewiththereturntothecustomer.InserttheJavaprogrammingoperationofthedatabasecanbereorientedwebsites,inordertoachievetheestablishmentofdynamicpagesneededtofunction.JSPandJavaServlet,isintheimplementationoftheserver,usuallyreturnedtotheclientisa

5、nHTMLtext,aslongastheclientbrowserwillbeabletovisit.JSP1.0specificationofthefinalversionislaunchedinSeptember1999,Decemberhasintroduced1.1specifications.AtpresentrelativelynewisJSP1.2norms,JSP2.0normsofthedrafthasalsobeenintroduced.JSPpagesfromHTMLcodeandJavacodeembeddedinoneofthecomponents.JSscript

6、languagesynopsisJSisjavascrip,JavascriptisonekindthescriptlanguagewhichcomesbytheNetscapeLiveScriptdevelopment,themainpurposeistosolvetheserverterminallanguage,forinstancePerl,carry-overspeedquestion.Atthattimeservedtheendtoneedtocarryontheconfirmationtothedata,becausethenetworkspeedwasquiteslow,onl

7、ythen28.8kbps,theconfirmationstepwastestimeweretoomany.ThereforeNetscapebrowserNavigatorhasjoinedJavascript,hasprovidedthedataconfirmationbasicfunction.TheJavaScriptofficialnameis“ECMAScript”.ThisstandardbyECMAorganizationdevelopmentandmaintenance.ECMA262istheofficialJavaScriptstandard.Thisstandardb

8、asedonJavaScript(Netscape)andJScript(Microsoft).Netscape(Navigator2.0)BrendanEichhasinventedthislanguage,startedfrom1996,alreadyappearedinallNetscapeandintheMicrosoftbrowser.TheECMA262developmentbeganin1996,in1997July,theECMAgeneralmeetinghasaccepteditsfirstedition.Thescriptusesonespecificdescriptiv

9、elanguage,restsoncertainformcompilationtobepossibletheexecutiondocument,isalsocalledasgreatorthebatchrundocument.Thescriptusuallymaytransfertemporarilybytheapplicationprocedureandcarryout.Eachkindofscriptpresentwidelyisappliedinthehomepagedesign,becausethescriptnotonlymayreducethehomepagethescaleand

10、raisesthehomepagebrowsingspeed,moreovermayenrichthehomepageperformance,likeanimation,soundandsoon.Citesamostcommonexample,whenweclickinthehomepagetheEmailaddresscantransferOutlookExpressortheFoxmailthiskindofmailsoftwareautomatically,isrealizesthroughthescriptfunction.Alsobecauseofscriptthesecharact

11、eristics,thehumanwhoharborsulteriormotivesbysomeareoftenusing.Forexamplejoinssomedestructioncomputersystemsorderinthescript,likethisworksastheuserbrowsinghomepage,oncetransfersthiskindofscript,willthencausetheuserthesystemtocomeundertheattack.Thereforetheusershouldactaccordingtovisitshomepagethetrus

12、tdegreeselectivesecurityrank,speciallyregardingtheseitselfcontentontheillegalhomepage,donotpermittheusescripteasily.Through“thesafeestablishment”thedialogbox,thechoice“thescript”underoptioneachkindofestablishmentmaywitheaserealizetoscriptbeingforbidandbeginsusing.JSPandServletsThetechnologyofJSPandS

13、ervletisthemostimportanttechnologywhichuseJavatechnologytoexploitrequestofserver,anditisalsothestandardwhichexploitbusinessapplication.Javadevelopersprefertouseitforavarietyofreasons,oneofwhichisalreadyfamiliarwiththeJavalanguageforthedevelopmentofthistechnologyareeasytolearnJavatotheotherisaprepara

14、tion,runeverywheretobringtheconceptofWebapplications,Toachieveaone-preparedeverywhererealized.Andmoreimportantly,iffollowedsomeoftheprinciplesofgooddesign,itcanbesaidofseparatingandcontenttocreatehigh-quality,reusable,easytomaintainandmodifytheapplication.Forexample,ifthedocumentinHTMLembeddedJavaco

15、detoomuch(script),willleadthedevelopedapplicationisextremelycomplex,difficulttoread,itisnoteasyreuse,butalsoforfuturemaintenanceandmodificationwillalsocausedifficulties.Infact,CSDNtheJSP/Servletforum,canoftenseesomequestions,thecodeisverylong,canlogicisnotveryclear,alargenumberofHTMLandJavacodemixed

16、together.Thisistherandomdevelopmentofthedefects.EarlydynamicpagesmainlyCGI(CommonGatewayInterface,publicGatewayInterface)technology,youcanusedifferentlanguagesoftheCGIprograms,suchasVB,C/C+orDelphi,andsoon.ThoughthetechnologyofCGIisdevelopedandpowerful,becauseofdifficultiesinprogramming,andloweffici

17、ency,modifycomplexshortcomings,itisgraduallybeingreplacedbythetrend.Ofallthenewtechnology,JSP/Servletwithmoreefficientandeasytoprogram,morepowerful,moresecureandhasagoodportability,theyhavebeenmanypeoplebelievethatthefutureisthemostdynamicsiteofthefuturedevelopmentoftechnology.SimilartoCGI,Servletsu

18、pportrequest/responsemodel.Whenacustomersubmitarequesttotheserver,theserverpresentedtherequestServlet,Servletresponsibleforhandlingrequestsandgeneratearesponse,andthengavetheserver,andthenfromtheserversenttothecustomer.AndtheCGIisdifferent,Servletnotgenerateanewprocess,butwithHTTPServeratthesameproc

19、ess.Itthreadsthroughtheuseoftechnology,reducetheservercosts.Servlethandlingoftherequestprocessisthis:Whenreceivedfromtheclientsrequest,callingservicemethods,themethodofServletarrivalofthefirstjudgementiswhattypeofrequest(GET/POST/HEAD),thencallstheappropriatetreatment(DoGet/doPost/doHead)andgenerate

20、aresponse.Althoughsuchacomplex,infact,simplysaidtoServletisaJavaclass.AndthegeneralcategoryofthedifferenceisthatthistypeoperatinginaServletcontainer,whichcanprovidesessionmanagementandtargetedlifecyclemanagement.SothatwhenyouusetheServlet,youcangetallthebenefitsoftheJavaplatform,includingthesafetyof

21、themanagement,useJDBCaccessthedatabaseandcrossplatformcapability.Moreover,Servletusingthread,andcandevelopmoreefficientWebapplications.JSPtechnologyisakeyJ2EEtechnology,itatahigherlevelofabstractionofaServlet.ItallowsconventionalstaticanddynamicHTMLcontentgeneratedbycombininganHTMLpagelookslike,buta

22、saServlettorun.TherearemanycommercialapplicationserversupportJSPtechnology,suchasBEAWebLogic,IBMWebSphere,JRun,andsoon.JSPandServletusemorethansimple.IfyouhaveaJSPsupportforWebservers,andaJSPdocument,youcanputitFangdaoanystaticHTMLfilescanbeplaced,donothavetocompile,donothavetopack,donothavetoClassP

23、athsettings,youcanvisitasordinaryWebItdidvisit,theserverwillautomaticallyhelpyoutodootherwork.JSPdocumentlookslikeanordinarystaticHTMLdocument,butinsidecontainsanumberofJavacode.Ituses.Jspthesuffix,usedtotelltheserverthisdocumentinneedofspecialtreatment.WhenwevisitaJSPpage,thedocumentwillfirstbetran

24、slatedintoaJSPengineJavasourcefiles,isactuallyaServlet,andcompiler,andthen,likeotherServlet,fromServletenginetohandle.Servletengineofthistypeloading,handlingrequestsfromcustomers,andtheresultsreturnedtothecustomer.Afteranothervisitthispagetothecustomer,aslongasthepapertherehavebeennochanges,JSPengin

25、ehasbeenloadeddirectlycalltheServlet.Ifyouhavealreadybeenmodified,itwillbeonceagaintheimplementationoftheaboveprocess,translate,compileandload.Infact,thisistheso-calledfirstpersontopunishment.Becausewhenthefirstvisittotheimplementationofaseriesoftheaboveprocess,sowillspendsometimeaftersuchavisitwoul

26、dnot.JavaservletsofferapowerfulAPIthatprovidesaccesstoalltheinformationabouttherequest,thesession,biningJSPwithservletsletsyouclearlyseparatetheapplicationlogicfromthepresentationoftheapplication;inotherwords,itletsyouusethemostappropriatecomponenttypefortherolesofModel,ViewandController.Servlets,Fi

27、lters,andListenersAservletisaJavaclassthatextendsaserverwithfunctionalityforprocessingarequestandproducingaresponse.ItsimplementedusingtheclassesandinterfacesdefinedbytheServletAPI.TheAPIconsistsoftwopackages:thejavax.servletpackagecontainsclassesandinterfacesthatareprotocolindependent,whilethejavax

28、.servlet.httppackageprovidesHTTP-specificextensionsandutilityclasses.Whatmakesaservletaservletisthattheclassimplementsaninterfacenamedjavax.servlet.Servlet,eitherdirectlyorbyextendingoneofthesupportclasses.Thisinterfacedefinesthemethodsusedbythewebcontainertomanageandinteractwiththe servlet.Aservlet

29、forprocessingHTTPrequeststypicallyextendsthejavax.servlet.http.HttpServletclass.ThisclassimplementstheServletinterfaceandprovidesadditionalmethodssuitableforHTTPprocessing.ServletLifecycleThewebcontainermanagesallaspectsoftheservletslifecycle.Itcreatesaninstanceoftheservletclasswhenneeded,passesrequ

30、eststotheinstanceforprocessing,andeventuallyremovestheinstance.ForanHttpServlet,thecontainercallsthefollowingmethodsattheappropriatetimesintheservletlifecycle.BesidesthedoGet()anddoPost()methods,therearemethodscorrespondingtotheotherHTTPmethods:doDelete(),doHead(),doOptions(),doPut(),anddoTrace().Ty

31、picallyyoudontimplementthesemethods;theHttpServletclassalreadytakescareofHEAD,OPTIONS,andTRACErequestsinawaythatssuitableformostservlets,andtheDELETEandPUTHTTPmethodsarerarelyusedinawebapplication.Itsimportanttorealizethatthecontainercreatesonlyoneinstanceofeachservlet.Thismeansthattheservletmustbet

32、hreadsafe-abletohandlemultiplerequestsatthesametime,eachexecutingasaseparatethreadthroughtheservletcode.Withoutgettinglostindetails,yousatisfythisrequirementwithregardstoinstancevariablesifyoumodifythereferencedobjectsonlyintheinit()anddestroy()methods,andjustreadthemintherequestprocessingmethods.Co

33、mpilingandInstallingaServletTocompileaservlet,youmustfirstensurethatyouhavetheJARfilecontainingallServletAPIclassesintheCLASSPATHenvironmentvariable.TheJARfileisdistributedwithallwebcontainers.Tomcatincludesitinafilecalledservlet.jar,locatedinthecommon/libdirectory.OnaWindowsplatform,youincludetheJA

34、RfileintheCLASSPATH.ReadingaRequestOneoftheargumentspassedtothedoGet()anddoPost()methodsisanobjectthatimplementstheHttpServletRequestinterface.Thisinterfacedefinesmethodsthatprovideaccesstoawealthofinformationabouttherequest.GeneratingaResponseBesidestherequestobject,thecontainerpassesanobjectthatim

35、plementstheHttpServletResponseinterfaceasanargumenttothedoGet()anddoPost()methods.Thisinterfacedefinesmethodsforgettingawriterorstreamfortheresponsebody.Italsodefinesmethodsforsettingtheresponsestatuscodeandheaders.UsingFiltersandListenersTheservletspecificationdefinestwocomponenttypesbesideservlets

36、:filtersandlisteners.ThesetwotypeswereintroducedintheServlet2.3specification,soifyoureusingacontainerthatdoesntyetsupportthisversionofthespecification,Imafraidyoure outofluck.FiltersAfilterisacomponentthatcaninterceptarequesttargetedforaservlet,JSPpage,orstaticpage,aswellastheresponsebeforeitssentto

37、theclient.Thismakesiteasytocentralizetasksthatapplytoallrequests,suchasaccesscontrol,logging,andchargingforthecontentortheservicesofferedbytheapplication.Afilterhasfullaccesstothebodyandheadersoftherequestandresponse,soitcanalsoperformvarioustransformations.Oneexampleiscompressingtheresponsebodyifth

38、e Acceptlanguagerequestheaderindicatesthattheclientcanhandleacompressedresponse.AfiltercanbeappliedtoeitheraspecificservletortoallrequestsmatchingaURLpattern,suchasURLsstartingwiththesamepathelementsorhavingthesameextension.ListenersListenersallowyourapplicationtoreacttocertainevents.PriortoServlet2

39、.3,youcouldhandleonlysessionattributebindingevents(triggeredwhenanobjectwasaddedorremovedfromasession).Youcoulddothisbylettingtheobjectsavedasasessionattributimplementthe HttpSessionBindingListenerinterface.Withthenewinterfacesintroducedinthe2.3versionofthespecification,youcancreatelistenersforservl

40、etcontextandsessionlifecycleeventsaswellassessionactivationandpassivationevents(usedbyacontainerthattemporarilysavessessionstatetodiskormigratesasessiontoanotherserver).Anewsessionattributeeventlisteneralsomakesitpossibletodealwithattributebindingeventsforallsessionsinoneplace,insteadofplacingindivi

41、duallistenerobjectsineachsession.ThenewtypesoflistenersfollowthestandardJavaeventmodel.Inotherwords,alistenerisaclassthatimplementsoneormoreofthelistenerinterfaces.Theinterfacesdefinemethodsthatcorrespondtoevents.Thelistenerclassisregisteredwiththecontainerwhentheapplicationstarts,andthecontainerthe

42、ncallstheeventmethodsattheappropriatetimes.InitializingSharedResourcesUsingaListenerBeanslikethistypicallyneedtobeinitializedbeforetheycanbeused.Forinstance,theymayneedareferencetoadatabaseorsomeotherexternaldatasourceandmaycreateaninitialinformationcacheinmemorytoprovidefastaccesseventothefirstrequ

43、estfordata.YoucanincludecodeforinitializationofthesharedresourcesintheservletandJSPpagesthatneedthem,butamoremodularapproachistoplaceallthiscodeinoneplaceandlettheotherpartsoftheapplicationworkontheassumptionthattheresourcesarealreadyinitializedandavailable.Anapplicationlifecyclelistenerisaperfectto

44、olforthistypeofresourceinitialization.Thistypeoflistenerimplementsthejavax.servlet.ServletContextListenerinterface,withmethodscalledbythecontainerwhentheapplicationstartsandwhenitshutsdown.PickingtheRightComponentTypeforEachTaskTheProjectBillboardapplicationintroducedisafairlycomplexapplication.Half

45、thepagesarepurecontrollerandbusinesslogicprocessing,itaccessesadatabasetoauthenticateusers,andmostpagesrequireaccesscontrol.Inreallife,itwouldlikelycontainevenmorepages,forinstance,pagesforaccesstoashareddocumentarchive,timeschedules,andasetofpagesforadministration.Astheapplicationevolves,itmaybecom

46、ehardtomaintainasapureJSPapplication.Itseasytoforgettoincludetheaccesscontrolcodeinnewpages.ThisisclearlyanapplicationthatcanbenefitfromusingacombinationofJSPpagesandthecomponenttypesdefinedbytheservletspecificationfortheMVCroles.Letslookatthemainrequirementsandseehowwecanmapthemtoappropriatecomponenttypes:Databaseaccessshouldbeabstracted,toavoidknowledgeofaspecificdataschemaordatabaseengineinmorethanonepartoftheapplication:beansintheroleofModelcanbeusedtoaccomplishthis.Thedatabaseaccessbeansmustbemadeavailabletoallotherpartsoftheapplicationwhenitstarts:anappli