翻译文献-介绍了ejb中会话bean的编程

外文原文INCHAPTERS35,WESCRATCHEDTHESURFACEOFEJBWITHANINTRODUCTIONTOSESSIONBEANPROGRAMMINGNOWTHATYOUVESEENTHEBAREBONESEXAMPLES,LETSPUTABITMOREMEATONOURBEANSINTHISCHAPTER,YOULLSEETHEFOLLOWING_HOWTOQUERYTHECONTAINERWITHEJBCONTEXTS_HOWTOUSEENVIRONMENTPROPERTIESTOCUSTOMIZEYOURBEANS,ANDACCESSTHOSEENVIRONMENTPROPERTIESATRUNTIME_HOWTOUSETHEEJBSECURITYMODEL_HOWTOUSEEJBOBJECTHANDLES_HOWTOCALLBEANSFROMOTHERBEANS_ANONTRIVIALEXAMPLEILLUSTRATINGEACHOFTHESECONCEPTS,USINGBOTHSTATELESSANDSTATEFULSESSIONBEANSLETSBEGINWITHALOOKATEJBCONTEXTSEJBCONTEXTSYOURGATEWAYTOTHECONTAINERASYOULLSEEONCEYOUBEGINYOUREJBDEVELOPMENT,NONTRIVIALENTERPRISEBEANSNEEDTODETERMINEINFORMATIONABOUTTHEIRCURRENTSTATUSATRUNTIMETHISCANINCLUDETHEFOLLOWING_INFORMATIONABOUTTHEBEANSHOMEOBJECTOREJBOBJECT_INFORMATIONABOUTANYTRANSACTIONTHEBEANISCURRENTLYINVOLVEDINFOREXAMPLE,IFTHECURRENTTRANSACTIONISGOINGTOFAIL,THEBEANCANSKIPUNNECESSARYCOMPUTATIONSTEPSADDINGFUNCTIONALITYTOYOURBEANS134MASTERINGENTERPRISEJAVABEANSGOBACKTOTHEFIRSTPAGEFORAQUICKLINKTOBUYTHISBOOKONLINE_SECURITYINFORMATIONFORCLIENTAUTHORIZATIONABEANCANQUERYITSENVIRONMENTTODETERMINEIFACLIENTHASTHEREQUIREDSECURITYACCESSLEVELTOPERFORMADESIREDOPERATION_ENVIRONMENTPROPERTIESTHATTHEBEANWASDEPLOYEDWITHTHECONTAINERHOUSESALLOFTHISINFORMATIONINONEOBJECT,CALLEDANEJBCONTEXTOBJECTANEJBCONTEXTOBJECTISYOURGATEWAYTOTHECONTAINEREJBCONTEXTSAREPHYSICALPARTSCONTAINERS,ANDCANBEACCESSEDFROMWITHINYOURBEANSTHUS,ACONTEXTREPRESENTSAWAYFORBEANSTOPERFORMCALLBACKSTOTHECONTAINERTHESECALLBACKSHELPBEANSBOTHASCERTAINTHEIRCURRENTSTATUSANDMODIFYTHEIRCURRENTSTATUSTHEMOTIVATIONBEHINDACONTEXTISTOENCAPSULATETHEBEANSDOMAININONECOMPACTOBJECTNOTETHATABEANSSTATUSMAYCHANGEOVERTHEBEANSLIECYCLE,ANDTHUSTHISCONTEXTOBJECTCANDYNAMICALLYCHANGEOVERTIMEASWELLATRUNTIME,THECONTAINERISRESPONSIBLEFORCHANGINGTHECONTEXTTOREFLECTANYSTATUSCHANGES,SUCHASTHEBEANBECOMINGINVOLVEDINANEWTRANSACTIONTHUS,YOUCANTHINKOFTHECONTEXTASAMIDDLEMANFORSTORINGSTATUSINFORMATIONABOUTABEANAMIDDLEMANTHATISPARTOFTHECONTAINERANDISQUERIEDBYTHEBEANHEREISWHATTHEEJB10JAVAXEJBEJBCONTEXTINTERFACELOOKSLIKEPUBLICINTERFACEJAVAXEJBEJBCONTEXTPUBLICJAVAXEJBEJBHOMEGETEJBHOMEPUBLICJAVAUTILPROPERTIESGETENVIRONMENTPUBLICJAVASECURITYIDENTITYGETCALLERIDENTITYPUBLICBOOLEANISCALLERINROLEJAVASECURITYIDENTITYPUBLICJAVAXJTSUSERTRANSACTIONGETUSERTRANSACTIONPUBLICVOIDSETROLLBACKONLYPUBLICBOOLEANGETROLLBACKONLYWESUMMARIZETHEMETHODSINJAVAXEJBEJBCONTEXTINTABLE61SESSIONBEANCONTEXTSANEJBCONTEXTCONTAINSCALLBACKSUSEFULFORBOTHSESSIONBEANSANDENTITYBEANSINCOMPARISON,ASESSIONCONTEXTISASPECIFICEJBCONTEXTUSEDONLYFORSESSIONBEANSENTITYBEANSHAVETHEIROWNEJBCONTEXT,TOO,CALLEDANENTITYCONTEXTBOTHSESSIONANDENTITYCONTEXTSDEFINEEXTRAMETHODSSPECIFICTOTHECORRESPONDINGKINDOFBEANADDINGFUNCTIONALITYTOYOURBEANS135GOBACKTOTHEFIRSTPAGEFORAQUICKLINKTOBUYTHISBOOKONLINEHEREISWHATTHESESSIONCONTEXTINTERFACELOOKSLIKEPUBLICINTERFACEJAVAXEJBSESSIONCONTEXTEXTENDSJAVAXEJBEJBCONTEXTPUBLICJAVAXEJBEJBOBJECTGETEJBOBJECTTABLE61JAVAXEJBEJBCONTEXTMETHODDESCRIPTIONGETHOMEYOURBEANSHOULDCALLGETHOMEWHENITNEEDSTOACCESSITSOWNHOMEOBJECTTHEBEANCANTHENUSEITSHOMEOBJECTTOCREATE,DESTROY,ORFINDEJBOBJECTSGETENVIRONMENTRETURNSALISTOFENVIRONMENTPROPERTIESTHATWEREDEPLOYEDWITHTHEBEANTHESEPROPERTIESCANBEUSEDTOSETARBITRARYINFORMATIONTHATABEANMAYNEED,SUCHASLOCATIONSOFFILESGETCALLERIDENTITYRETURNSTHESECURITYIDENTITYOFTHECLIENTTHATISINVOKINGMETHODSONTHEBEANINSTANCESEJBOBJECTYOUCANUSETHECLIENTSIDENTITYFORMANYTHINGSFOREXAMPLE,YOUCANRETRIEVETHECALLERSDISTINGUISHEDNAME,ANDUSEITASAKEYTOUNLOCKSECUREDINFORMATIONINADATABASEISCALLERINROLERETURNSWHETHERTHEAUTHENTICATEDCLIENTISAUTHORIZEDTOPERFORMANOPERATIONTHECLIENTMUSTBEINTHECORRECTSECURITYROLE,WHICHISAGROUPAUTHORIZEDTOPERFORMCERTAINOPERATIONSSETROLLBACKONLYALLOWSTHEINSTANCETOMARKTHECURRENTTRANSACTIONSUCHTHATTHEONLYOUTCOMEOFTHETRANSACTIONISAROLLBACKGETROLLBACKONLYRETURNSABOOLEANINDICATINGWHETHERTHECURRENTTRANSACTIONHASBEENMARKEDFORROLLBACKIFITSGOINGTOABORT,YOUMAYBEABLETOBYPASSLOGICINYOURBEAN,SAVINGVALUABLECOMPUTATIONTIMEGETUSERTRANSACTIONUSETHISMETHODIFYOUWANTTOWRITECODEINYOURBEANTOCONTROLTRANSACTIONSONCEYOUCALLTHISMETHOD,YOURBEANCANCONTROLNOTETHISMETHODISTRANSACTIONSUSINGTHERETURNEDJAVAXTRANSACTIONUSERTRANSACTIONONLYSUPPORTEDFOROBJECTYOUCANTHENBEGIN,COMMIT,ANDROLLBACKTRANSACTIONSBEANSTHATPERFORMEXPLICITLYTHEIROWNTRANSACTIONSWELLLEARNMOREABOUTTHISMETHODINCHAPTER10136MASTERINGENTERPRISEJAVABEANSGOBACKTOTHEFIRSTPAGEFORAQUICKLINKTOBUYTHISBOOKONLINENOTICETHATTHESESSIONCONTEXTINTERFACEEXTENDSTHEEJBCONTEXTINTERFACE,GIVINGSESSIONBEANSACCESSTOALLTHEMETHODSTHATWEDEFINEDABOVEINEJBCONTEXTTHEONEEXTRAMETHODISGETEJBOBJECTASWESAWINCHAPTER3,ALLSESSIONBEANSANDENTITYBEANSMUSTEXPOSEAMETHODTHATTHECONTAINERWILLCALLTOASSOCIATETHEBEANWITHAPARTICULARCONTEXTFORSESSIONBEANS,THISMETHODISCALLEDSETSESSIONCONTEXTSESSIONCONTEXTCTXTHISMETHODISDEFINEDINTHEJAVAXEJBSESSIONBEANINTERFACETHATWESHOWEDYOUINCHAPTER3ASWEWILLSEEINCHAPTER7,ENTITYBEANSHAVEASIMILARMETHODCALLEDSETENTITYCONTEXTENTITYCONTEXTCTXSESSIONCONTEXTGETEJBOBJECTINEJB,BEANSCANACTASCLIENTSOFOTHERBEANSTHEGETEJBOBJECTMETHODISUSEFULIFYOURBEANNEEDSTOCALLANOTHERBEANANDIFYOUWANTTOPASSAREFERENCETOYOUROWNBEANINJAVA,ANOBJECTCANOBTAINAREFERENCETOITSELFWITHTHETHISKEYWORDINEJB,THOUGH,ABEANCANNOTUSETHETHISKEYWORDANDPASSITTOOTHERBEANSBECAUSEALLCLIENTSINVOKEMETHODSONBEANSINDIRECTLYTHROUGHBEANSEJBOBJECTTHUS,ABEANCANREFERTOITSELFBYUSINGAREFERENCETOITSEJBOBJECT,RATHERTHANTHETHISKEYWORDUNDERSTANDINGEJBSECURITYTHENEXTTOPICWECOVERISADDINGSECURITYTOYOURENTERPRISEBEANSLETSGETRIGHTDOWNTOTHEMEATTHEREARETWOSECURITYMEASURESTHATCLIENTSMUSTPASSWHENYOUADDSECURITYTOANEJBSYSTEMFIRST,THECLIENTMUSTBEAUTHENTICATEDAUTHENTICATIONVERIFIESTHATTHECLIENTISWHOHECLAIMSTOBEFORINSTANCE,THECLIENTMAYENTERAUSERNAME/PASSWORDINAWEBBROWSER,ANDTHOSECREDENTIALSARECHECKEDAGAINSTAPERMANENTCLIENTPROFILESTOREDINADATABASEORLDAPSERVERONCETHECLIENTISAUTHENTICATED,HEISASSOCIATEDWITHASECURITYIDENTITYFORTHEREMAINDEROFHISSESSIONTHEN,THECLIENTMUSTBEAUTHORIZEDONCETHECLIENTHASBEENAUTHENTICATED,HEMUSTHAVEPERMISSIONTOPERFORMDESIREDOPERATIONSFOREXAMPLE,INAPROCUREMENTAPPLICATION,YOUDWANTTOENSURETHATWHILEANYONECANSUBMITPURCHASEORDERS,ONLYSUPERVISORSCANAPPROVEPURCHASEORDERSTHEREISAVERYIMPORTANTDIFFERENCEHEREAUTHENTICATIONVERIFIESTHATTHECLIENTISWHOHECLAIMSTOBE,WHEREASAUTHORIZATIONCHECKSTOSEEIFANALREADYAUTHENTICATEDCLIENTISALLOWEDTOPERFORMATASKAUTHENTICATIONMUSTBEPERFORMEDSOMETIMEBEFOREANEJBMETHODISCALLEDIFTHECLIENTHASANIDENTITY,THENITHASBEENAUTHENTICATEDAUTHORIZATION,ONTHEOTHERHAND,OCCURSDURINGANEJBMETHODCALLADDINGFUNCTIONALITYTOYOURBEANS137GOBACKTOTHEFIRSTPAGEFORAQUICKLINKTOBUYTHISBOOKONLINESTEP1AUTHENTICATIONEJBDOESNOTHELPYOUWITHAUTHENTICATIONTHESPECIFICWAYYOURCLIENTCODEBECOMESASSOCIATEDWITHASECURITYIDENTITYISLEFTTOTHEDISCRETIONOFYOURAPPLICATIONANDYOUREJBCONTAINERTHISMEANSEACHEJBCONTAINERMAYHANDLEAUTHENTICATIONDIFFERENTLYFOREXAMPLE,WITHBEAWEBLOGICYOURCLIENTCODECANSPECIFYITSUSERNAMEANDPASSWORDWHENITUSESJNDITOLOOKUPHOMEOBJECTS,ASSHOWNINTHEFOLLOWINGCODEPROPERTIESPROPSSYSTEMGETPROPERTIESPROPSPUTCONTEXTSECURITY_PRINCIPAL,“EMPLOYEEA“PROPSPUTCONTEXTSECURITY_CREDENTIALS,“MYPASSWORD1“CONTEXTCTXNEWINITIALCONTEXTPROPS/USETHEINITIALCONTEXTTOLOOKUPHOMEOBJECTSSINCETHEEJBSPECIFICATIONDOESNOTSPECIFYHOWTOPERFORMAUTHENTICATION,THISCODEISNOTPORTABLETOOTHERAPPLICATIONSERVERSCHECKYOURCONTAINERSDOCUMENTATIONFORAUTHENTICATIONINSTRUCTIONSWHENYOURUNTHISCODE,THEAPPLICATIONSERVERMUSTMAPYOURUSERNAMEANDMPASSWORDTOASECURITYIDENTITYAGAIN,THISSTEPISAPPLICATIONSERVERSPECIFICSOMEAPPLICATIONSERVERSALLOWYOUTOSETUPUSERNAMESANDPASSWORDSINTHEAPPLICATIONSERVERSPROPERTIESFILETHATTHEAPPLICATIONSERVERREADSINATRUNTIMEMOREADVANCEDSERVERSSUPPORTCOMPLEXINTEGRATIONWITHEXISTINGSECURITYSYSTEMS,SUCHASALISTOFUSERNAMESANDPASSWORDSSTOREDINANLDAPSERVERASANACADEMICEXAMPLE,HEREISHOWTOSPECIFYUSERNAMESANDPASSWORDSUSINGBEAWEBLOGICSWEBLOGICPROPERTIESFILENOTETHATTHISISINSUFFICIENTFORREALDEPLOYMENTSTHATNEEDTOMAPTOREALSECURITYSYSTEMS,SUCHASANITSHOPSEXISTINGLISTOFEMPLOYEEUSERNAMES/PASSWORDSWEBLOGICPASSWORDEMPLOYEEAMYPASSWORD1WEBLOGICPASSWORDEMPLOYEEBMYPASSWORD2STEP2AUTHORIZATIONONCETHECLIENTHASBEENAUTHENTICATED,ITMUSTTHENPASSANAUTHORIZATIONTESTTOCALLMETHODSONYOURBEANSTHEREARETWOWAYSTOPERFORMAUTHORIZATIONWITHEJBDECLARATIVELYORPROGRAMMATICALLYWITHDECLARATIVEAUTHORIZATION,THECONTAINERPERFORMSALLAUTHORIZATIONCHECKSFORYOUEFFECTIVELYYOUAREDELEGATINGAUTHORIZATIONTOTHEEJBCONTAINERTHISKEEPSYOURBEANCODELEANANDALLOWSYOUTOFOCUSONYOURBUSINESSLOGIC,RATHERTHANFOCUSONWRITINGSECURITYCHECKS138MASTERINGENTERPRISEJAVABEANSGOBACKTOTHEFIRSTPAGEFORAQUICKLINKTOBUYTHISBOOKONLINEWITHPROGRAMMATICAUTHORIZATION,YOUHARDCODESECURITYCHECKSINTOYOURBEANCODEYOURBUSINESSLOGICISINTERLACEDWITHSECURITYCHECKS,BLOATINGYOURBEANCODESECURITYROLESAUTHORIZATIONINEJBRELIESONSECURITYROLESASECURITYROLEISACOLLECTIONOFCLIENTIDENTITIESFORACLIENTTOBEAUTHORIZEDTOPERFORMANOPERATION,ITSSECURITYIDENTITYMUSTBEINTHECORRECTSECURITYROLEFORTHATOPERATIONTHEEJBDEPLOYERISRESPONSIBLEFORASSOCIATINGTHEIDENTITIESWITHTHECORRECTSECURITYROLESAFTERYOUWRITEYOURBEANSTHEADVANTAGETOUSINGSECURITYROLESISYOUDONOTHARDCODESPECIFICIDENTITIESINTOYOURBEANSTHISISNECESSARYWHENYOUAREDEVELOPINGBEANSFORDEPLOYMENTINAWIDEVARIETYOFSECURITYENVIRONMENTS,BECAUSEEACHENVIRONMENTWILLHAVEITSOWNLISTOFIDENTITIESTHISALSOALLOWSYOUTOMODIFYACCESSCONTROLWITHOUTRECOMPILINGYOURBEANCODESPECIFYINGSECURITYROLESINEJBISAGAINAPPLICATIONSERVERSPECIFICTHEFOLLOWINGEMONSTRATESHOWTODOITWITHBEASWEBLOGICSERVERINTHEWEBLOGICPROPERTIESFILEWEBLOGICSECURITYGROUPEMPLOYEESEMPLOYEEA,EMPLOYEEBWEBLOGICSECURITYGROUPMANAGERSMANAGERAWEBLOGICSECURITYGROUPADMINISTRATORSADMINATHEAPPLICATIONSERVERQUERIESTHESEGROUPSATRUNTIMEWHENPERFORMINGAUTHORIZATIONDECLARATIVEAUTHORIZATIONWITHDECLARATIVEAUTHORIZATION,YOUDECLAREYOURBEANSAUTHORIZATIONREQUIREMENTSINYOURDEPLOYMENTDESCRIPTORTHECONTAINERWILLFULFILLTHESEREQUIREMENTSATRUNTIMEFOREXAMPLE,TAKETHEFOLLOWINGSAMPLEDEPLOYMENTDESCRIPTORENTRYUSINGBEASWEBLOGICSERVERACCESSCONTROLENTRIESSUBMITPURCHASEORDEREMPLOYEESAPPROVEPURCHASEORDERMANAGERSDEFAULTADMINISTRATORSENDACCESSCONTROLENTRIESTHEFIRSTENTRYSPECIFIESTHATALLIDENTITIESAUTHORIZEDASEMPLOYEESCANSUBMITPURCHASEORDE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