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Que using enterprise javabeans 2 0 special edition sep 2001 ISBN 0789725673







TableofContents



Examples

SpecialEditionUsingEnterpriseJavaBeans™
2.0
ByChuckCavaness,BrianKeeton




Publisher


:Que

PubDate

:September19,2001

ISBN

:0-7897-2567-3

Pages

:648

Slots

:1



SpecialEditionUsingEnterpriseJavaBeans2.0startswitha
descriptionofhowEnterpriseJavaBeansfitsintothebigpicture
ofJ2EEdevelopment,thencoverssuchtopicsas:
LocatingEJB'susingJNDI
ManagingdatawithEJBQueryLanguage
BuildingJMSapplicationsusingthenewMessage-driven
Bean
PlanningEJBapplicationsusingdesignpatterns
Laterchaptersdescribeadvanceddevelopmenttopicsincluding
interoperability,horizontalservicesandclustering.Throughout
thebook,theauthorsconstructacomponent-basedauction
websiteusingtheJ2EEarchitectureasapracticalexample.









TableofContents



Examples

SpecialEditionUsingEnterpriseJavaBeans™
2.0
ByChuckCavaness,BrianKeeton




Publisher

:Que

PubDate

:September19,2001

ISBN

:0-7897-2567-3

Pages

:648

Slots

:1



Copyright



AbouttheAuthors



Acknowledgments



TellUsWhatYouThink!



Introduction









ThisBookIsforYou
HowThisBookIsOrganized
ConventionsUsedinThisBook


PartI:DevelopingEnterpriseJavaBeans














Chapter1.IntroductiontoEnterpriseApplications








Chapter2.SettingtheStage–AnExampleAuctionSite




Chapter3.EJBConcepts

TheEnterpriseJavaBeansArchitecture
Component-BasedDistributedComputing
N-TieredArchitectures
WhyUseEJB?









TheAuctionExample
OverviewofanEnglishAuction
ChoosingtheUseCasestoImplement
DefiningtheObjectModel
What'sNext?





GraspingtheConceptsEarly








WhatIsanEnterpriseBean?
















EJBRolesandTheirResponsibilities













LocalVersusRemoteEJBClients
UsingRMItoCommunicatewithEnterpriseJavaBeans
AccessinganEJBThroughItsComponentInterface
LocatingEnterpriseBeansUsingtheHomeInterface
DecidingWhethertoUseaLocalorRemoteClient
CreationandRemovalofEJBs
PassivationandActivation
ObjectPooling
Handles
TheEJBMetaDataClass
EJBServerandContainerImplementations
































Chapter4.JavaNamingandDirectoryInterface










Chapter5.EntityBeans







Chapter6.Bean-ManagedPersistence

WhyApplicationsNeedNamingandDirectoryServices
OverviewoftheJNDIArchitecture
SelectingandConfiguringaJNDIProvider
TheJNDIEnvironmentProperties
SettingtheJNDIEnvironmentProperties
TheContextandInitialContextObjects
GettingtheEnvironmentforaContextObject
UsingthelookupMethodtoLocateJNDIResources
LocatingEJBObjects
AccessinganEJB'sEnvironment
EstablishingSecurityThroughtheInitialContext
JNDIandClustering
Troubleshooting











WhatIsanEntityBean?
DeclaringtheComponentInterface
DefiningthePrimaryKeyClass
DeclaringtheHomeInterface
ImplementinganEntityBean
InheritanceandEntityBeans
AreEntityBeansWorthIt?








ChoosingtoManagePersistenceYourself
JDBCPrimer
ConfiguringaDataSource
CreatinganEntityBean






LoadingandStoringanEntity









AccessingOtherEntityBeans






ImplementingFinderMethods
DeletinganEntity
DeployinganEntityBeanUsingBMP
Troubleshooting




















Chapter7.Container-ManagedPersistence










Chapter8.EJBQueryLanguage






Chapter9.SessionBeans

BuildingPortableEntityBeans
DeclaringaCMPEntityBean
ImplementingtheContainerCallbackMethods
DeployinganEntityBeanUsingCMP
ManagingRelationships
UsingEJB1.1CMP
Troubleshooting











WhatIstheEJBQueryLanguage?
DefiningaFROMClause
DefiningaWHEREClause
DefiningaSELECTClause
UsingtheBuilt-InFunctions
EJBQLSyntaxinBNFNotation
Troubleshooting












WhatIsaSessionBean?
DifferencesBetweenStatelessandStatefulSessionBeans
DeclaringtheComponentInterface







DeclaringtheHomeInterface










Chapter10.JavaMessageService

ImplementingaSessionBean
DeployingaSessionBean
ReentrantIssues
Troubleshooting











IntroductiontoMessaging
ComponentsoftheJMSArchitecture
TheTwoJMSMessageModels
TheJMSInterfaces
TheDetailsofaJMSMessage
MessageSelectionandFiltering
UsingtheJMSPoint-to-PointModel












UsingtheJMSPublish/SubscribeModel







SynchronousVersusAsynchronousMessaging
MessagePersistence
UsingTransactionswithJMS
UsingJMSwithEnterpriseJavaBeans
Troubleshooting


























Chapter11.Message-DrivenBeans











Chapter12.Transactions









Chapter13.ExceptionHandling







Chapter14.SecurityDesignandManagement

WhatAreMessage-DrivenBeans?
TheMessage-DrivenBeanandtheContainer
UsingMessage-DrivenBeanswithEJB
UsingJMSQueuesorTopicswithMessage-DrivenBeans
CreatingaMessage-DrivenBean
DeployingaMessage-DrivenBean
SendingMessagestoaMessage-DrivenBean
AcknowledgingMessagesfromMessage-DrivenBeans
UsingTransactionswithMessage-DrivenBeans
Troubleshooting












UnderstandingTransactions
PassingtheACIDTest
ProgrammingwiththeJavaTransactionAPI
UsingContainer-ManagedTransactions
UsingBean-ManagedTransactions
UsingClient-DemarcatedTransactions
IsolatingAccesstoResources
Troubleshooting










EJBExceptionHandling
ApplicationExceptions
SystemExceptions
ExceptionsandTransactions
PackagingExceptions
Troubleshooting








TheImportanceofApplicationSecurity
UnderstandingYourApplication'sSecurityRequirements
BasicSecurityConcepts
JavaSecurityFundamentals






UsingSecuritywithEnterpriseJavaBeansandJ2EE





SketchingOuttheAuctionSecurity





JavaAuthenticationandAuthorizationService(JAAS)


















Chapter15.Deployment
DeploymentDescriptorsandEJBRoles
BeanProviderResponsibilities
ApplicationAssemblerResponsibilities
DeployerResponsibilities
PackagingEJBs
Troubleshooting



PartII:DesignandPerformance


















Chapter16.PatternsandStrategiesinEJBDesign









Chapter17.AddressingPerformance








Chapter18.PerformanceandStressTestingYourApplications

WhatArePatterns?
StrategiesforEnterpriseJavaBeans
DesigningEJBClassesandInterfaces
ManagingClientAccess
ImplementingaSingletoninEJB
Troubleshooting










TheRoleofPerformanceinDesign
MinimizingRemoteCalls
OptimizingEntityBeanPersistence
BuildingaPickList
ManagingTransactions
Troubleshooting









WhyStressTestYourApplications?
PerformanceTestingYourBeans
StressTestingYourBeans
UsingECperf1.0
Troubleshooting



PartIII:BuildingtheWebTier










Chapter19.BuildingaPresentationTierforEJB
TheDifferentTypesofPresentationTiers
UsingaFaçadePatterntoHideEJB
UsingServletsandJavaServerPageswithEJB










UsingJSPTagLibraries






UsingtheStrutsOpen-SourceFramework



CachingontheWebServerorinStatefulSessionBeans



PartIV:AdvancedConcepts






















Chapter20.DistributionandEJBInteroperability











Chapter21.HorizontalServices








Chapter22.EJBClusteringConcepts






Chapter23.EJB2.0ProgrammingRestrictions

InteroperabilityOverview
PortabilityVersusInteroperability
EJB2.0InteroperabilityGoals
TheRelationshipBetweenCORBAandEnterpriseJavaBeans
RemoteInvocationInteroperability
TransactionInteroperability
NamingInteroperability
SecurityInteroperability












WhatAreHorizontalServices?
HorizontalServicesProvidedbyEJB
TraditionalBuyVersusBuildAnalysis
AuctionExampleHorizontalServices
BuildingtheAuctionLoggingService
Java1.4LoggingAPI
BuildinganE-MailHorizontalService
Troubleshooting









TooMuchIsn'tAlwaysaGoodThing
WhatIsClustering?
ClusteringintheWebTier
ClusteringintheEJBTier
SingleVMVersusMultipleVMArchitectures







ThePurposeoftheRestrictions
TheEJB2.0Restrictions
Summary



PartV:Appendixes








AppendixA.TheEJB2.0API
Interfaces






Exceptions





Thejavax.ejb.spiPackage
















AppendixB.ChangesfromEJB1.1
LocalClients





Message-DrivenBeans





HomeInterfaceBusinessMethods

Container-ManagedPersistenceChanges
EJBQueryLanguage

SecurityChanges
ComponentInteroperability


Copyright
Copyright©2002byQue®Corporation
Allrightsreserved.Nopartofthisbookshallbereproduced,
storedinaretrievalsystem,ortransmittedbyanymeans,
electronic,mechanical,photocopying,recording,orotherwise,
withoutwrittenpermissionfromthepublisher.Nopatent
liabilityisassumedwithrespecttotheuseoftheinformation
containedherein.Althougheveryprecautionhasbeentakenin
thepreparationofthisbook,thepublisherandauthorassume
noresponsibilityforerrorsoromissions.Norisanyliability
assumedfordamagesresultingfromtheuseoftheinformation
containedherein.
LibraryofCongressCatalogCardNumber:2001087886
PrintedintheUnitedStatesofAmerica
FirstPrinting:September2001
040302014321

Trademarks
Alltermsmentionedinthisbookthatareknowntobe
trademarksorservicemarkshavebeenappropriately
capitalized.QueCorporationcannotattesttotheaccuracyof
thisinformation.Useofaterminthisbookshouldnotbe
regardedasaffectingthevalidityofanytrademarkorservice
mark.
JavaBeansisatrademarkofSunMicrosystems.

WarningandDisclaimer
Everyefforthasbeenmadetomakethisbookascompleteand


asaccurateaspossible,butnowarrantyorfitnessisimplied.
Theinformationprovidedisonan"asis"basis.Theauthorsand
thepublishershallhaveneitherliabilitynorresponsibilitytoany
personorentitywithrespecttoanylossordamagesarising
fromtheinformationcontainedinthisbookorfromtheuseof
theCDorprogramsaccompanyingit.

Credits
AssociatePublisher
DeanMiller
AcquisitionsEditor
ToddGreen
DevelopmentEditor
SeanDixon
ManagingEditor
ThomasF.Hayes
ProjectEditor
TonyaSimpson
CopyEditor
SossitySmith
Indexer
BillMyers


Proofreaders
KayleneRiemen
HarveyStanbrough
Plan-ItPublishing
TechnicalEditors
AlanMoffet
TimDrury
StevenHaines
JonHassell
GrantHolland
AlexKachur
TeamCoordinator
CindyTeeters
MediaDeveloper
MichaelHunter
InteriorDesigner
RuthHarvey
CoverDesigners
DanArmstrong


RuthHarvey
PageLayout
MarkWalchle

Dedication
FromChuck
Tomymom,whogavemeeverythingthatachildneedsto
grow.TomywifeTracyandmytwoboys,JoshuaandZachary,
thanksforallthepoking,prodding,andnaggingtokeepwriting
whenitwashardtofindtheenergy.Alsoabigthankstomy
co-author,Brian,forbeingagreatpersontowriteabookwith
andsuchagoodfriend.
FromBrian
TomywifeRebeccahanddaughterEmilyforyourloveand
patience,myparentsforyourunconditionalsupport,andmy
sisterDonnawhocallsmeageekonlyoccasionally.


AbouttheAuthors
ChuckCavanessisaJavaArchitectatNetVendorInc,aB2B
SupplierEnablementCompanyspecializingintheElectronics,
Aerospace,andAutomotiveindustrieslocatedinAtlanta,
Georgia.Hisareaofexpertisespansserver-sideJava,
distributedobjectcomputing,andapplicationservers.Currently,
hemoderatesthe"JavaintheEnterprise"discussionforumat
JavaWorld.Hehasalsotaughtobject-orientedcoursesatthe
GeorgiaInstituteofTechnologyandspentseveralyearswriting
SmalltalkandCORBAsoftware.Chuckearnedhisdegreein
ComputerSciencefromtheGeorgiaInstituteofTechnology.
Chuckisco-authorofSpecialEditionUsingJava2Standard
Edition.
BrianKeetonisaJavaArchitectatNetVendorInc.wherehe
developscomponentstosupportB2BtradingusingEJB.Heisa
SunCertifiedJavaDeveloperwithovertenyearsofprofessional
softwaredevelopmentexperience.Hespentfiveyears
developingobject-orientedapplicationsinC++forthedefense
industrybeforetransitioningtodistributedapplication
developmentusingCORBAandEJB.BrianearnedhisMasterof
ScienceinElectricalEngineeringfromGeorgiaTechandiscoauthorofSpecialEditionUsingJava2StandardEdition.


Acknowledgments
Wewouldliketogivethankstothemanyindividualswho
helpedmakethisbookpossible.Writingabookisateameffort
andwewerefortunatetohaveagreatteamthatwassincerely
interestedinmakingthematerialinthisbookasinformative
andaccurateaspossible.
Firstandforemost,wewouldliketothankalltheeditorswho
painstakinglyreadthrougheverychapter,page,paragraph,and
sentencetohelpmoldourthoughtsandramblingsintowhat
youwillhopefullyfindaveryenjoyableandworthwhilejourney.
Weespeciallywanttorecognizethetechnicaleditors,whosejob
itwastopourthroughmorethanafewvoluminous
specificationsanddocumentstoensurethatweneverstrayed
toofarfromreality:GrantHolland,StevenHaines,JonHassell,
AlexKachur,AlanMoffet,andTimDrury.Wearealsogreatly
appreciativeoftheworkdonebyourprojecteditorTonya
SimpsonandcopyeditorSossitySmithandforMichaelHunter's
workinsecuringthesoftwarefortheCD.Thequalityandpolish
ofthisbookaretotheircredit(andanymistakesareours
alone).
WewouldliketoinparticularthankToddGreenandSeanDixon
forgivingusenoughropetohangourselvesandfortrusting
thatweknewwhatweweredoingfromthebeginning.Your
patiencewasdearlyappreciated.
Finally,wewouldliketocollectivelythankourfamiliesand
friendsfortheunderstandingandsupportthroughouttheentire
process.Itwouldn'thavebeenpossiblewithoutyourundying
support.


TellUsWhatYouThink!
Asthereaderofthisbook,youareourmostimportantcritic
andcommentator.Wevalueyouropinionandwanttoknow
whatwe'redoingright,whatwecoulddobetter,whatareas
you'dliketoseeuspublishin,andanyotherwordsofwisdom
you'rewillingtopassourway.
AsanassociatepublisherforQue,Iwelcomeyourcomments.
Youcanfax,e-mail,orwritemedirectlytoletmeknowwhat
youdidordidn'tlikeaboutthisbook—aswellaswhatwecan
dotomakeourbooksstronger.
PleasenotethatIcannothelpyouwithtechnicalproblems
relatedtothetopicofthisbook,andthatduetothehigh
volumeofmailIreceive,Imightnotbeabletoreplytoevery
message.
Whenyouwrite,pleasebesuretoincludethisbook'stitleand
authoraswellasyournameandphoneorfaxnumber.Iwill
carefullyreviewyourcommentsandsharethemwiththe
authorsandeditorswhoworkedonthebook.
Fax:

317-581-4666

E-mail:

feedback@quepublishing.com

Mail:

DeanMiller
QuePublishing
201West103rdStreet
Indianapolis,IN46290USA


Introduction
Inthischapter
ThisBookIsforYou
HowThisBookIsOrganized
ConventionsUsedinThisBook
WelcometoEnterpriseJavaBeans2.0!AspartoftheJava2
EnterpriseEdition(J2EE),theEnterpriseJavaBeansarchitecture
hasbecometheacceptedstandardforthedevelopmentof
distributed,mission-criticalbusinessapplications.The
EnterpriseJavaBeans(EJB)specificationturnsJ2EEapplication
serversintoafoundationforbuildingapplicationsthatare
secure,transactional,scalable,andportable.Ifyoudevelop
large-scalebusinesssystemsandyou'veneverusedEJB,nowis
thetimetojointhemomentumthat'sthrivingonanevergrowingnumberofsuccessstories.IfyoualreadyuseEJB,the
2.0Specificationoffersyouevenmoreinthewayof
productivityandcomponentportability.
WhatisEJB?EJBisaspecificationforaserver-sidecomponent
architecture.NottobeconfusedwithregularJavaBeans,EJBs
areindustrial-strengthcomponentsthatencapsulatereusable
businesslogicandaccesstoexternalresourcessuchas
relationaldatabasesforanenterprise.Foremostamongthe
goalsforEJBisthatitmakesitpossiblefordeveloperstofocus
onbusinesslogicwithouthavingtoworryaboutthelow-level
detailsofthelifecycle,transactional,security,andpersistence
needsoftheirapplications.Theserequirementsarehandledfor
youinawaythatenablesyoutocreatecomponentsthatare
portableacrossapplicationservers—thusmeetinganothergoal
ofthearchitecture.Ontopofeverythingelse,EJBtakesstock
inthefactthatthevalueofacomponentoftenismeasuredin
termsofitsreusability.EJBtakesadeclarativeapproachfor


deployingapplicationsthatsupportsextensivecustomizationof
componentswithoutrequiringchangestothecode.
TheEJBspecificationwasfirstintroducedbySunMicrosystems
alone,butithasnowmaturedtoitscurrentformthroughthe
JavaCommunityProcess(JCP).Benefitingfromthe
participationoftheleadingapplicationserverandsoftware
vendors,EJB2.0willalmostcertainlycontinuethesuccessof
thearchitecture.


ThisBookIsforYou
Thisbookistargetedforemosttowardprogrammerswhoknow
JavabutarenewtoEJB.EJBisacomplextopic,butthe
chaptersthatfollowareorganizedtobuildyourknowledgeof
theunderlyingtechnologiesasawaytogetyoustarted.When
youhaveafoundation,detaileddiscussionsandexamples
introduceyoutowhatyouneedtobuildyourskillsasanEJB
developerbeforemovingontomoreadvancedtopics.
AlthoughprogrammerswithoutexperienceinEJBshouldfeelat
homewiththisbook,thisismorethanabeginner's
introduction.IfyoualreadyknowEJB,you'relikelyawarethat
theEJB2.0Specificationhasintroducedsignificantchangesin
severalkeyareasofthearchitecture(checkoutAppendixB,
"ChangesfromEJB1.1,"ifyouwantasummary).Forthoseof
youwhoarefamiliarwithEJB,thisbookwillteachyouhowto
takeadvantageofwhat'snew.Italsowillexposeyoutoseveral
provenEJBdesignpracticesthataretakingshapewithinthe
industry.IfyoualreadyuseEJB1.1andareconsideringmoving
totheEJB2.0Specification,thisbookpointsoutsome
importantissuesyoushouldconsiderbeforemovingyour
architecture.Ifyou'vealreadydecidedtostaywithEJB1.1for
nowandarejustwantingtogetuptospeedonwhat'scoming
with2.0,thisbookcanalsohelpguideyourtransitionfrom1.1
to2.0whenyou'reready.


HowThisBookIsOrganized
Thisbookisorganizedintofivepartsthatwalkyouthroughthe
conceptsbehindEJBandtheprocessofdesigningand
implementingyourownenterprisebeans.Relatedtopicshave
beenorganizedtobuildyourknowledgeofEJBprogrammingas
youprogressthroughthebook.
PartI,"DevelopingEnterpriseJavaBeans,"teachesyouthe
mechanicsofbuildingEJBclassesandtheirinterfaces.Thispart
beginswithanoverviewofcomponent-baseddevelopmentand
describestheroleofEJBwithinamultitierarchitecture.The
chaptersthatfollowintroduceeachoftheenterprisebeantypes
withdetailedexamplesthatteachyouwhatyouneedtoknow
tobeginbuildinganddeployingyourownEJBs.Tobesureyou
understandtheotherJ2EEtechnologiesthatEJBrelieson
directly,separatechaptersprovidein-depthcoverageofthe
JavaNamingandDirectoryInterface(JNDI)andtheJava
MessageService(JMS).Thispartalsodefinestheroleof
transactionswithinEJBapplicationsanddescribesexception
handlingandsecuritymanagement.
PartII,"DesignandPerformance,"goesbeyondthebasicsof
buildingEJBsandintroducesyoutoasetofdesignand
performancestrategiestoapplytoyourenterprisedevelopment
efforts.AlthoughEJBisarelativelynewtechnology,thereare
alreadystandardpracticesemergingthatyoumustbeawareof
asadesigner.Thispartalsoincludesadiscussionofseveral
approachesyoucantaketostresstestyourapplications.
PartIII,"BuildingtheWebTier,"crossestheboundaryofwhat
youmightexpecttoseeinanEJBbook.Thechapterincluded
herelooksatseveralpatternsyoucanapplytobuildinga
servlet-andJSP-basedpresentationtierthatinteractswithan
applicationtierbuiltusingEJB.
PartIV,"AdvancedConcepts,"getsyouuptospeedonthe


concernsofexperiencedEJBdevelopers.Hereyou'llget
informationonanewrequirementintroducedwithEJB2.0that
makesitpossibleforanEJBtocommunicatewithCORBA
objectsorEJBsrunninginanothervendor'scontainer.You'll
alsobeintroducedtosomerecommendedpracticesforbuilding
afoundationalservicelayerforyourapplications.Tobuildon
theperformancechapterinPartII,you'llalsolearnabout
clusteringofEJBcomponentsandserviceshere.Thefinal
chapterinPartIVwillespeciallyinterestyouifyou'rethetype
ofpersonwhoalwayswantstoknowwhywhensomeonetells
younottodosomething.Thischapterlooksinparticularatthe
thingsyou'renotsupposedtodowithintheEJBcontainerand
why.
PartV,"Appendixes,"offerssomequick-referencematerialthat
includesasummaryoftheEJB2.0APIandadescriptionof
what'schangedsinceEJB1.1.


ConventionsUsedinThisBook
Thisbookusesvariousstylisticandtypographicconventionsto
makeiteasiertouse.
Note
Whenyouseeanoteinthisbook,itindicates
additionalinformationthatcanhelpyoubetter
understandatopicoravoidproblemsrelatedtothe
subjectathand.

Tip
Tipsintroducetechniquesappliedbyexperienced
developerstosimplifyataskortoproduceabetter
design.Thegoalofatipistohelpyouapply
standardpracticesthatleadtorobustand
maintainableapplications.

Caution
Cautionswarnyouofhazardousprocedures(for
example,actionsthathavethepotentialto
compromisethesecurityofasystem).

Cross-referencesareusedthroughoutthebooktohelpyou
quicklyaccessrelatedinformationinotherchapters.


Foranintroductiontotheterminologyassociatedwith
transactions,see"UnderstandingTransactions,"p.332.
Manyofthechaptersinthisbookconcludewitha
"Troubleshooting"sectionthatprovidessolutionstosomeofthe
commonproblemsthatyoumightencounterregardinga
particulartopic.Throughoutthemainchaptertext,crossreferencessuchastheseareincludedtodirectyoutothe
appropriateheadingwithinthe"Troubleshooting"sectionto
addresstheseproblems.


PartI:DevelopingEnterpriseJavaBeans
1IntroductiontoEnterpriseApplications
2SettingtheStage—AnExampleAuctionSite
3EJBConcepts
4JavaNamingandDirectoryInterface
5EntityBeans
6Bean-ManagedPersistence
7Container-ManagedPersistence
8EJBQueryLanguage
9SessionBeans
10JavaMessageService
11Message-DrivenBeans
12Transactions
13ExceptionHandling
14SecurityDesignandManagement
15Deployment


Chapter1.IntroductiontoEnterpriseApplications
Inthischapter
TheEnterpriseJavaBeansArchitecture
Component-BasedDistributedComputing
N-TieredArchitectures
WhyUseEJB?


TheEnterpriseJavaBeansArchitecture
TheEJB2.0SpecificationdefinesEnterpriseJavaBeans(EJB)as
anarchitectureforcomponent-baseddistributedcomputing.
Althoughthisdefinitionworkswellifyouarealreadyfamiliar
withtermssuchascomponent-basedanddistributed
computing,thedefinitiondoesn'thelpmuchifyouarebrandnewtoEnterpriseJavaBeansorenterpriseapplication
development.Itmightevenbehelpfultodefinewhatismeant
byanenterpriseapplication.Beforewedothat,however,let's
getapictureofwhattheEJBarchitecturelookslike.Thisway,
you'llhaveanimageinyourheadaswegothroughthis
discussion.Figure1.1illustratestheEJBarchitecturefroma
highlevel.
Figure1.1.Ahigh-levelviewoftheEJBarchitecture.


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