英文技术文献 jsp.docx

英文技术文献 jsp.docx

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英文技术文献jsp

Thetitleofthebook:

《JavaServerPagesTM,ThirdEdition》.

Author:

HansBergsten.

Press:

O’ReillyMedia，Inc.

Source:

.

Chapter18.WebApplicationModels

PartIIofthisbookdescribeshowyoucancreatemanydifferenttypesofapplicationsusingonlyJSPpageswithgenericcomponents—JSTLactions,customactionsandbeans—toaccessdatabases,presentcontentindifferentlanguages,protectpages,andsoforth—allwithoutknowingmuchaboutJavaprogramming.Thisapproachworksfineformanytypesofwebapplications,suchasemployeeregisters,productcatalogs,andconferenceroomreservationsystems.Butforapplicationswithcomplicatedschemas,intricatebusinessrules,andtrickycontrolflows,thegenericcomponentsjustdon'tcutit,andyousuddenlyfindthatyouneedamorepowerfulwaytohandletherequestprocessingandthebusinesslogic.

AsImentionedinChapter3,JSPcanbecombinedwithotherJavatechnologiessuchasservletsandEJBinmorecomplexapplications.Inthischapter,welookathowJSPfitsintothislargerpicture.Afterthebriefdescriptionofthemostcommonapplicationmodelsinthischapter,Chapter19describesthecombinationofservletsandJSPindetail.

ThematerialpresentedinthispartofthebookisgearedtowardsJavaprogrammers.Ifyou'renotaprogrammer,youmaystillwanttobrowsethroughthisparttogetafeelforthepossibilities,butdon'texpecttounderstandeverything.Toreallyappreciatethetechniquesdescribedinthispartofthebook,youshouldhaveexperiencewithJavaprogrammingingeneral.FamiliaritywithJavaservletsalsohelps,andashortintroductionisincludedinChapter19forthosewhoarenewtothistechnology.

18.1TheJava2EnterpriseEditionModel

AttheJavaOneconferenceinSanFranciscoinJune1999,SunMicrosystemsannouncedanewarchitectureforJava,withseparateeditionsfordifferenttypesofapplications:

theJava2StandardEdition（J2SE）fordesktopandworkstationdevices;theJava2MicroEdition（J2ME）forsmalldevicessuchascellphones,pagers,andPDAs;andtheJava2EnterpriseEdition（J2EE）forserver-basedapplications.

J2EEisacompilationofvariousJavaAPIsthathavepreviouslybeenofferedasseparatepackages;anApplicationProgrammingModel（APM）（alsoknownastheJ2EEBlueprints）thatdescribeshowtheycanallbecombined;andatestsuiteJ2EEvendorscanusetotesttheirproductsforcompatibility.J2EEhasgonethroughanumberofrevisionssince1999,andthelatestversion（J2EE1.4）includesthefollowingenterprise-specificAPIsamongothers:

∙JavaServerPages（JSP）

∙JavaServlet

∙EnterpriseJavaBeans（EJB）

∙JavaDatabaseConnection（JDBC）

∙JavaTransactionAPI（JTA）andJavaTransactionService（JTS）

∙JavaNamingandDirectoryInterface（JNDI）

∙JavaMessageService（JMS）

∙JavaIDLandRemoteMethodInvocation（RMI）

∙JavaAPIforXMLParsing（JAXP）,JavaAPIforXML-basedRPC（JAX-RPC）,SOAPwithAttachmentsAPIforJava（SAAJ）,andJavaAPIforXMLRegistries（JAXR）

∙JavaMailandJavaBeansActivationFramework（JAF）

∙J2EEConnectorArchitecture（JCX）

∙JavaAuthenticationandAuthorizationService（JAAS）

∙JavaManagementExtensions（JMX）

Inaddition,alltheJ2SEAPIscanbeusedwhendevelopingaJ2EEapplication.TheseAPIscanbeusedinnumerouscombinations.ThefirstthreeJ2EEAPIs—EJB,JSP,andservlets—representdifferentcomponenttechnologies,managedbywhattheJ2EEdocumentscallcontainers.AwebcontainerprovidestheruntimeenvironmentforservletsandJSPcomponents,translatingrequestsandresponsesintostandardJavaobjects.EJBcomponentsaresimilarlyhandledbyanEJBcontainer.Don'tbefooledbythenamesimilaritybetweenJavaBeansandEnterpriseJavaBeans（EJB）;theyarecompletelydifferentanimals.AJavaBeanscomponentisaregularJavaclass,followingafewsimplenamingconventions,whichcanbeusedbyanyotherJavaclass.AnEnterpriseJavaBeancomponent,ontheotherhand,mustbedevelopedincompliancewithawholesetofstrictrulesandworksonlyintheenvironmentprovidedbyanEJBcontainer.

ComponentsinthetwotypesofcontainerscanusetheotherJ2EEAPIstoaccessdatabases（JDBCandJTA/JTS）andotherEIStierapplications（JCX）,authenticateusersandcontrolaccess（JAAS）,locatevariousresources（JNDI）,andcommunicatewithotherserverresources（JavaMail/JAF,JMS,JavaIDL,RMI,JAXP,JAX-RPC,SAAJandJAXR）.Enterpriseapplicationsareoftendividedintoasetoftiers,andJ2EEidentifiesthree:

theclienttier,themiddletier,andtheEnterpriseInformationSystem（EIS）tier.ThemiddletiercanbefurtherdividedintothewebtierandtheEJBtier.Thislogicalseparation,withwell-definedinterfaces,makesitpossibletobuildscalableapplications.Initiallyoneormoretierscanberunningonthesamephysicalserver.Withincreaseddemands,thetierscanbeseparatedanddistributedovermultipleserverswithoutmodifyingthecode,justbychangingtheconfiguration.

TheclienttiercontainsbrowsersaswellasregularGUIapplications.AbrowserusesHTTPtocommunicatewiththewebcontainer.AstandaloneapplicationcanalsouseHTTPorcommunicatedirectlywiththeEJBcontainerusingRMIorIIOP（aCORBAprotocol）.Anothertypeofclientthat'sbecomingmoreandmorepopularistheextremelythinclient,suchasacellphoneorPDA.ThistypeofclienttypicallyusestheWirelessAccessProtocol（WAP）,typicallyconvertedintoHTTPviaagateway,tocommunicatewiththewebcontainer.

ThemiddletierprovidesclientservicesthroughthewebcontainerandtheEJBcontainer.AclientthatcommunicateswiththeserverthroughHTTPusescomponentsinthewebcontainer,suchasservletsandJSPpages,asentrypointstotheapplication.Manyapplicationscanbeimplementedsolelyaswebcontainercomponents.Inotherapplications,thewebcomponentsjustactasaninterfacetotheapplicationlogicimplementedbyEJBcomponents.Astandaloneapplication,writteninJavaoranyotherprogramminglanguage,canalsocommunicatedirectlywiththeEJBcomponents.Generalguidelinesforwhentousethedifferentapproachesarediscussedlaterinthischapter.ComponentsinthistiercanaccessdatabasesandcommunicatewithotherserverapplicationsusingalltheotherJ2EEAPIs.

TheEnterpriseInformationSystem（EIS）tierholdstheapplication'sbusinessdata.Typically,itconsistsofoneormorerelationaldatabasemanagementservers,butothertypesofdatabasessuchasIMSdatabases;legacyapplicationssuchasEnterpriseResourcePlanning（ERP）;andmainframetransactionprocessingsystemssuchasCICS,arealsoincludedinthistier.ThemiddletierusesJ2EEAPIssuchasJDBC,JTA/JTS,andtheJ2EEConnectorArchitecture（JCX）tointeractwiththeEIStier.

18.2TheMVCDesignModel

Inadditiontotheseparationofresponsibilitiesintodifferenttiers,J2EEalsoencouragestheuseoftheModel-View-Controller（MVC）designmodel,brieflyintroducedinChapter3,whendesigningapplications.

TheMVCmodelwasfirstdescribedbyXeroxinanumberofpaperspublishedinthelate1980sinconjunctionwiththeSmalltalklanguage.ThismodelhassincebeenusedforGUIapplicationsdevelopedinallpopularprogramminglanguages.Let'sreview:

thebasicideaistoseparatetheapplicationdataandbusinesslogic,thepresentationofthedata,andtheinteractionwiththedataintodistinctentitieslabeledtheModel,theView,andtheController,respectively.

TheModelrepresentspurebusinessdataandtherulesforhowtousethisdata;itknowsnothingabouthowthedataisdisplayedortheuserinterfaceformodifyingthedata.TheView,ontheotherhand,knowsallabouttheuserinterfacedetails.ItalsoknowsaboutthepublicModelinterfaceforreadingitsdata,sothatitcanrenderitcorrectly,anditknowsabouttheControllerinterface,soitcanasktheControllertomodifytheModel.

Usinganemployeeregistryapplicationasanexample,anEmployeeclassmayrepresentaModel.Itholdsinformationaboutanemployee:

name,employmentdate,vacationdays,salary,etc.Italsoholdsrulesforhowthisinformationcanbechanged;forinstance,thenumberofvacationdaysmaybelimitedbasedontheemploymenttime.TheuserinterfacethatshowstheinformationisaView.ItgetsholdofanEmployeeobjectbyaskingtheControllerforitandthenrenderstheinformationbyaskingtheEmployeeobjectforitspropertyvalues.TheViewalsorenderscontrolsthatallowtheusertomodifytheinformation.TheViewssendsthemodificationrequesttotheController,whichupdatestheEmployeeobjectandthentellstheViewthattheModelhasbeenmodified.TheView,finally,updatestheuserinterfacetodisplaytheupdatedvalues.

UsingtheMVCdesignmodelmakesforaflexibleapplicationarchitecture,inwhichmultiplepresentations（Views）canbeprovidedandeasilymodified,andchangesinthebusinessrulesorphysicalrepresentationofthedata（theModel）canbemadewithouttouchinganyoftheuserinterfacecode.

EventhoughthemodelwasoriginallydevelopedforstandaloneGUIapplications,ittranslatesfairlywellintothemultitierapplicationdomainofJ2EE.TheuserinteractswiththeControllertoaskforthingstobedone,andtheControllerrelaystheserequeststotheModelinaclient-typeindependentway.Say,forinstance,thatyouhavetwotypesofclients:

anHTTPclientsuchasabrowserandaGUIclientapplicationusingIIOPtotalktotheserver.InthisscenarioyoucanhaveoneControllerforeachprotocolthatreceivestherequestsandextractstherequestinformationinaprotocol-dependentmanner.BothControllersthencalltheModelthesameway;theModeldoesn'tneedtoknowwhatkindof