翻译文献-javabean 的发展

外文原文THEENTERPRISEJAVABEANSINAJ2EEAPPLICATIONENTERPRISEJAVABEANSEJBTIERHOSTSAPPLICATIONSPECIFICBUSINESSLOGICANDPROVIDESSYSTEMLEVELSERVICESSUCHASTRANSACTIONMANAGEMENT,CONCURRENCYCONTROL,ANDSECURITYENTERPRISEJAVABEANSTECHNOLOGYPROVIDESADISTRIBUTEDCOMPONENTMODELTHATENABLESDEVELOPERSTOFOCUSONSOLVINGBUSINESSPROBLEMSWHILERELYINGONTHEJ2EEPLATFORMTOHANDLECOMPLEXSYSTEMLEVELISSUESTHISSEPARATIONOFCONCERNSALLOWSRAPIDDEVELOPMENTOFSCALABLEACCESSIBLE,ROBUST,ANDHIGHLYSECUREAPPLICATIONSINTHEJ2EEPROGRAMMINGMODELEJBCOMPONENTSAREAFUNDAMENTALLINKBETWEENPRESENTATIONCOMPONENTSHOSTEDBYTHEWEBTIERANDBUSINESSCRITICALDATAANDSYSTEMSMAINTAINEDINTHEENTERPRISEINFORMATIONSYSTEMTIERTHISCHAPTERDESCRIBESTHECONCEPTSCENTRALTOTHEENTERPRISEJAVABEANSARCHITECTUREANDPROVIDESGUIDELINESANDRECOMMENDATIONSTOBESTUSEEJBCOMPONENTSTHECHAPTEREXAMINESTHENATUREOFBUSINESSLOGICANDDESCRIBESTHEPROBLEMSADEVELOPERNEEDSTORESOLVEWHENIMPLEMENTINGBUSINESSLOGICDESCRIBESTHECOMPONENTMODELTHATENTERPRISEJAVABEANSARCHITECTUREPROVIDESTOADDRESSTHESEPROBLEMSDESCRIBESREMOTEANDLOCALCLIENTVIEWSPROVIDESDETAILSONTHETHREETYPESOFENTERPRISEBEANSENTITYBEANS,SESSIONBEANS,ANDMESSAGEDRIVENBEANSRECOMMENDSDESIGNGUIDELINESFORDEVELOPINGEJBCOMPONENTSANDAPPLICATIONSPRESENTSRECOMMENDATIONSANDPRACTICESTOBESTUTILIZETHEEJBTIERSERVICESPROVIDEDBYTHEJ2EEPLATFORMPROVIDESGUIDELINESTOFACILITATEAPPLICATIONPORTABILITY51BUSINESSLOGICANDBUSINESSOBJECTSBUSINESSLOGIC,INAVERYBROADSENSE,ISTHESETOFPROCEDURESORMETHODSUSEDTOMANAGEASPECIFICBUSINESSFUNCTIONTAKINGTHEOBJECTORIENTEDAPPROACHENABLESTHEDEVELOPERTODECOMPOSEABUSINESSFUNCTIONINTOASETOFCOMPONENTSORELEMENTCALLEDBUSINESSOBJECTSLIKEOTHEROBJECTS,BUSINESSOBJECTSHAVEBOTHSTATEORDATAANDBEHAVIORFOREXAMPLE,ANEMPLOYEEOBJECTHASDATASUCHASANAMEADDRESS,SOCIALSECURITYNUMBER,ANDSOONITHASMETHODSFORASSIGNINGITTOANEWDEPARTMENTORFORCHANGINGITSSALARYBYACERTAINPERCENTAGETOMANAGEABUSINESSPROBLEMYOUMUSTBEABLETOREPRESENTHOWSUCHBUSINESSOBJECTSFUNCTIONANDINTERACTTOPROVIDETHEDESIREDFUNCTIONALITYTHESETOFBUSINESSSPECIFICRULESTHATHELPIDENTIFYTHESTRUCTUREANDBEHAVIOROFTHEBUSINESSOBJECTS,ALONGWITHTHEPREANDPOSTCONDITIONSTHATMUSTBEMETWHENANOBJECTEXPOSESITSBEHAVIORTOOTHEROBJECTSINTHESYSTEM,ISKNOWNASBUSINESSLOGICTHEFOLLOWINGDISCUSSIONDEMONSTRATESHOWTODEFINETHESTRUCTUREANDBEHAVEFOROFABUSINESSOBJECTFROMTHEREQUIREMENTSIMPOSEDBYTHEBUSINESSPROBLEMITADDRESSESFOREXAMPLE,THESAMPLEAPPLICATIONUSESAGROUPOFBUSINESSOBJECTSACATALOGOBJECTTOSHOWAVAILABLEPETSASHOPPINGCARTOBJECTTOTEMPORARILYHOLDACLIENTSSELECTIONOFPETSANACCOUNTOBJECTTOKEEPINFORMATIONABOUTACLIENTORDEROBJECTSTOKEEPTRACKOFPLACEDORDERSUSINGTHEACCOUNTOBJECTASANEXAMPLE,ITSREQUIREMENTSINCLUDE1EACHCLIENTMUSTHAVEAUNIQUEACCOUNT2EACHACCOUNTSHOULDHAVECONTACTINFORMATIONFORACLIENTSUCHASNAME,STREETADDRESS，ANDEMAILADDRESS3CLIENTSMUSTBEABLETOCREATENEWACCOUNTSANDCLOSEORREMOVEACCOUNTS4CLIENTSMUSTBEABLETOUPDATECONTACTINFORMATIONFORTHEIRACCOUNTS5CLIENTSMUSTBEABLETORETRIEVEINFORMATIONFORTHEIRACCOUNTS6CLIENTSCANRETRIEVEANDUPDATEONLYTHEIROWNACCOUNTINFORMATION7THEACCOUNTINFORMATIONMUSTBEMAINTAINEDINPERSISTENTSTORAGE8MULTIPLECLIENTSMUSTBEABLETOACCESSTHEIRACCOUNTINFORMATIONATTHESAMETIME9MULTIPLECLIENTSCANNOTUPDATETHESAMEACCOUNTCONCURRENTLYTHEFIRSTTWOREQUIREMENTSSPECIFYTHESTRUCTURALATTRIBUTESOFTHEACCOUNTOBJECTFOLLOWINGTHESERULES,THEACCOUNTOBJECTSHOULDHAVEAFIELDTOHOLDACCOUNTIDENTIFICATIONANDSEVERALOTHERFIELDSTOHOLDADDRESS,PHONE,ANDOTHERCONTACTINFORMATIONTHEBEHAVIOROFTHEACCOUNTOBJECTISDESCRIBEDINREQUIREMENTSTHREE,FOURANDFIVEFOREXAMPLE,ACCOUNTSSHOULDHAVEMETHODSTOCREATEANEWACCOUNT,TOUPDATECONTACTINFORMATION,ANDTOGETTHEACCOUNTINFORMATIONTHELASTFOURREQUIREMENTSSPECIFYGENERALCONDITIONSTHATMUSTBEMETSOTHATTHEACCOUNTOBJECTCANPROPERLYCARRYOUTITSFUNCTIONALITYFOREXAMPLE,WHENACLIENTUPDATESANACCOUNT,THECLIENTSHOULDBEAUTHORIZEDTOACCESSTHATPARTICULARACCOUNTANDUPDATEDACCOUNTINFORMATIONSHOULDBEWRITTENTOPERSISTENTSTORAGENOOTHERCLIENTSHOULDBEABLETOACCESSTHEPARTICULARACCOUNTCONCURRENTLYSIMILARANALYSISANDREQUIREMENTDEFINITIONSCOULDBEPERFORMEDFOROTHEROBJECTSFOREXAMPLE,ANORDEROBJECTHASASETOFGENERALCONDITIONSONITSBEHAVEFORTHATHAVEASIGNIFICANTCORRELATIONTOTHEBEHAVIOROFANACCOUNTOBJECTTHATISCLIENTNEEDSTOBEAUTHORIZEDBEFOREUPDATINGORREADINGTHESTATUSOFANORDER,DETAILSNEEDTOBEWRITTENTOAPERSISTENTSTORAGE,ANDSOONIFYOUEXAMINEBUSINESSOBJECTSINSIMILARAPPLICATIONSYOUWILLSEETHATEVENTHOUGHTHEACTUALSTRUCTUREANDBEHAVIOROFTHEOBJECTISTIEDCLOSELYTOTHEBUSINESSPROBLEMITISGOINGTOSOLVE,MANYSERVICESTHATTHESEBUSINESSOBJECTSPROVIDEFOLLOWSPECIFICPATTERNSTHATAREQUITEGENERICINNATURE511COMMONREQUIREMENTSOFBUSINESS06JECTSTHISSECTIONDESCRIBESCOMMONREQUIREMENTSOFBUSINESSOBJECTS5111MAINTAINSTATEABUSINESSOBJECTOFTENNEEDSTOMAINTAINSTATEBETWEENMETHODINVOCATIONSTHISSTATECANBEEITHERCONVERSATIONALORPERSISTENTCONVERSATIONALSTATEISSTATEMAINTAMEDINANOBJECTDURINGTHECONVERSATIONBETWEENACLIENTANDTHEAPPLICATIONPERSISTENTSTATEISSTATETHATISSTOREDINADATABASEOROTHERPERSISTENTSTORE,OUTLIVINGTHECONVERSATIONBETWEENACLIENTANDTHEAPPLICATIONCONSIDERASHOPPINGCARTOBJECTTHESTATEOFTHESHOPPINGCARTOBJECTREPRESENTSTHEITEMSANDQUANTITIESOFTHEITEMSPURCHASEDBYTHECLIENTTHECARTISINITIALLYEMPTYANDGAINSMEANINGFULSTATEWHENAUSERADDSANITEMTOTHECARTWHENAUSERADDSASECONDITEMTOTHECART,THECARTSHOULDHAVEBOTHITEMSINITSIMILARLY,WHENAUSERDELETESANITEMFROMTHECART,THECARTSHOULDREFLECTTHECHANGEINITSSTATEWHENAUSEREXITSTHEAPPLICATION,THECARTOBJECTISRECLAIMEDANDTHECONVERSATIONALSTATENOLONGEREXISTSWHENTHEOBJECTGAINS,MAINTAINS,ANDLOSESITSSTATEASARESULTOFREPEATEDINTERACTIONSWITHTHESAMECLIENT,WESAYTHEOBJECTMAINTAINSCONVERSATIONALSTATETOUNDERSTANDPERSISTENTSTATE,CONSIDERANACCOUNTOBJECTWHENAUSERCREATESANACCOUNT,THEACCOUNTINFORMATIONNEEDSTOBESTOREDPERMANENTLYSOTHATWHENTHEUSEREXITSTHEAPPLICATIONANDREENTERSTHEAPPLICATION,THEACCOUNTINFORMATIONCANBEPRESENTEDTOTHEUSERAGAINTHESTATEOFANACCOUNTOBJECTNEEDSTOBEMAINTAINEDINPERSISTENTSTORAGE,SUCHASADATABASETHATWILLSURVIVESYSTEMCRASHES5112OPERATEONSHAREDDATAANOTHERCOMMONCHARACTERISTICOFBUSINESSOBJECTSISTHATTHEYOFTENOPERATEONSHAREDDATAINTHISCASE,MEASURESMUSTBETAKENTOPROVIDECONCURRENCYCONTROLANDAPPROPRIATELEVELSOFISOLATIONFORACCESSTOTHESHAREDDATAANEXAMPLEOFSUCHASCENARIOWOULDBEMULTIPLEUSERSUPDATINGTHESAMEACCOUNTINFORMATIONIFTWOUSERSTRYTOUPDATETHESAMEACCOUNTATTHESAMETIME,AMECHANISMMUSTBEUSEDTOKEEPTHEDATAINACONSISTENTSTATE5113PARTICIPATEINTRANSACTIONSATRANSACTIONCANBEDESCRIBEDASASETOFTASKSTHATNEEDTOBECOMPLETEDASAUNITIFONEOFTHETASKSFAILS,ALLTHETASKSINTHEUNITWILLBEROLLEDBACKIFALLOFTHEMSUCGEED,THETRANSACTIONISSAIDTOBECOMMITTEDBUSINESSOBJECTSOFTENNEEDTOPARTICIPATEINTRANSACTIONSFOREXAMPLE,ORDERPLACEMENNEEDTOBETRANSACTIONALBECAUSEOFTHESETOFTASKSREQUIREDTOCOMPLETEANORDERDECREMENTINGTHEQUANTITYOFTHEPURCHASEDITEMININVENTORYSTORINGTHEORDERDETAILS,ANDSENDINGANORDERCONFIRMATIONTOTHEUSERFORTHETRANSACTIONTOBECOMPLETED,ALLOFTHESETASKSMUSTSUCCEEDIFANYONEOFTHESETASKSFAILS,WORKDONEBYOTHERTASKSNEEDSTOBEUNDONEINMANYBUSINESSOPERATIONS,TRANSACTIONSMAYSPANMORETHANONEREMOTEDATASOURCESUCHTRANSACTIONSALLDISTRIBUTEDTRANSACTIONSREQUIRESPECIALPROTOCOLSTOENSUREDATAINTEGRITYCHAPTER8DISCUSSESTHEISSUESINVOLVEDINTRANSACTIONMANAGEMENT5114SERVICEALARGENUMBEROFCLIENTSABUSINESSOBJECTSHOULDBEABLETOPROVIDEITSSERVICESTOALARGENUMBEROFCLIENTSATTHESAMETIMETHISTRANSLATESINTOAREQUIREMENTFORINSTANCEMANAGEMENTALGORITHMSTHATGIVEEACHCLIENTANIMPRESSIONTHATADEDICATEDBUSINESSOBJECTISAVAILABLETOSERVICEITSREQUESTWITHOUTSUCHAMANAGEMENTMECHANISM,THESYSTEMWILLEVENTUALLYRUNOUTOFRESOURCESANDWILLNOTBEABLETOSERVICEANYMORECLIENTS51。15REMAINAVAILABLETOCLIENTSABUSINESSOBJECTSHOULDREMAINAVAILABLETOCLIENTSEVENWHENSYSTEMSCRASH,ASERVICEREFERREDTOASHIGHAVAILABILITYTHEEJBCONTAINERINWHICHABUSINESSOBJECTRESIDESPROVIDESTHISSERVICEBYUTILIZINGSTRATEGIESTOMASKVARIOUSSERVERERRORSFROMTHECLIENTS5116PROVIDEREMOTEACCESSTODATAACLIENTSHOULDBEABLETOREMOTELYACCESSSERVICESOFFEREDBYABUSINESSOBJECTTHISMEANSTHATTHEBUSINESSOBJECTSHOULDHAVESOMETYPEOFINFRASTRUCTURETOSUPPORTSERVICINGCLIENTSOVERTHENETWORKTHISINTURNIMPLIESTHATABUSINESSOBJECTSHOULDBEPARTOFADISTRIBUTEDCOMPUTINGENVIRONMENTTHATTAKESCAREOFFINDISSUESINDISTRIBUTEDSYSTEMS,SUCHASLOCATIONANDFAILURETRANSPARENCY5117CONTROLACCESSTHESERVICESOFFEREDBYBUSINESSOBJECTSOFTENREQUIRESOMETYPEOFCLIENTAUTHENTICATIONANDAUTHORIZATIONMECHANISMTOALLOWONLYACERTAINSETOFCLIENTSTOACCESSPROTECTEDSERVICESFOREXAMPLE,ITSHOULDBEVERIFIEDTHATACLIENTISAUTHORIZEDTOUPDATEACCOUNTINFORMATIONINANACCOUNTBUSINESSOBJECTBEFOREALLOWINGITTODOSOINMANYENTERPRISESCENARIOS,DIFFERENTLEVELSOFACCESSCONTROLARENEEDEDFOREXAMPLE,EMPLOYEESSHOULDONLYBEALLOWEDTOVIEWTHEIROWNSALARYOBJECTS,WHILEAPAYROLLADMINISTRATORCANVIEWASWELLASMODIFYALLSALARYOBJECTS5118REUSABLEACOMMONREQUIREMENTOFBUSINESSOBJECTSISTHATTHEYBEREUSABLEBYDIFFERENTCOMPONENTSOFTHESAMEAPPLICATIONAND/ORBYDIFFERENTAPPLICATIONSFOREXAMPLE,ANAPPLICATIONUSEDBYTHEPAYROLLDEPARTMENTTOKEEPTRACKOFEMPLOYEESALARYMAYHAVETWOBUSINESSOBJECTSEMPLOYEEANDSALARYASALARYBUSINESSOBJECTMAYUSETHESERVICESOFANEMPLOYEEBUSINESSOBJECTTOGETTHEGRADELEVELOFANEMPLOYEEANAPPLICATIONTHATTRACKSTHEEMPLOYEEVACATIONALLOWANCESMAYWANTTOUSETHISEMPLOYEEOBJECTTOGETTHENAMEOFTHEEMPLOYEETHROUGHTHEEMPLOYEENUMBERBUSINESSOBJECTSAREABLETOBEUSEDBYINTERANDINFRAAPPLICATIONCOMPONENTSWHENTHEYAREDEVELOPEDINASTANDARDWAYANDRUNINANENVIRONMENTTHATABIDESBYTHESESTANDARDSIFTHESESTANDARDSAREWIDELYADOPTEDBYTHEVENDORCOMMUNITY,ANAPPLICATIONCANBEASSEMBLEDFROMOFFTHESHELFCOMPONENTSFROMDIFFERENTVENDORSINADDITIONTOENABLINGRAPIDAPPLICATIONDEVELOPMENT,THISAPPROACHHELPSDEVELOPERSAVOIDVENDORLOCKIN52ENTERPRISEBEANSASJ2EEBUSINESSOBJECTSASDISCUSSEDINTHEPREVIOUSSECTION,BUSINESSOBJECTSNEEDTOPROVIDESOMEGENERICSERVICESTOCLIENTS,SUCHASSUPPORTFORTRANSACTIONS,SECURITY,ANDREMOTEACCESSTHESECOMMONSERVICESARECOMPLEXINNATUREANDAREOUTSIDETHEDOMAINOFTHEBUSINESSLOGICREQUIREDTOIMPLEMENTANAPPLICATIONTOSIMPLIFYDEVELOPMENT,ENTERPRISEAPPLICATIONSNEEDASTANDARDSERVERSIDEINFRASTRUCTURETHATCANPROVIDESUCHSERVICESTHEEJBTIEROFTHEJ2EEPLATFORMPROVIDESASTANDARDSERVERSIDEDISTRIBUTEDCOMPONENTMODELTHATGREATLYSIMPLIFIESTHETASKOFWRITINGBUSINESSLOGICINTHEEJBARCHITECTURE,SYSTEMEXPERTSPROVIDETHEFRAMEWORKFORDELIVERINGSYSTEMLEVELSERVICES,ANDAPPLICATIONDOMAINEXPERTSPROVIDETHECOMPONENTSTHATHOLDBUSINESSSPECIFICKNOWLEDGETHEJ2EEPLATFORMENABLESENTERPRISEDEVELOPERSTOCONCENTRATEONSOLVINGTHEPROBLEMSOFTHEENTERPRISEINSTEADOFEXPENDINGTHEIREFFORTSONSYSTEMLEVELISSUESTHEENTERPRISEJAVABEANSARCHITECTUREDEFINESCOMPONENTSCALLEDENTERPRISEBEANSTHATALLOWTHEDEVELOPERTOWRITEBUSINESSOBJECTSTHATUSETHESERVICESPROVIDEDBYTHEJ2EEPLATFORMTHEREARETHREEKINDSOFENTERPRISEBEANSSESSIONBEANS,ENTITYBEANS,ANDMESSAGEDRIVENBEANSSESSIONBEANSAREINTENDEDTOBEPRIVATERESOURCESUSEDONLYBYTHECLIENTTHATCREATESTHEMFORTHISREASON,SESSIONBEANS,FROMTHECLIENTSPERSPECTIVE,APPEARANONYMOUSENTITYBEANSARECOMPONENTSTHATREPRESENTANOBJECTORIENTEDVIEWOFSOMEENTITIESTHATARESTOREDINPERSISTENTSTORAGE,SUCHASADATABASEINCONTRASTTOSESSIONBEANS,EVERYENTITYBEANHASAUNIQUEIDENTITYTHATISEXPOSEDASAPRIMARYKEYMESSAGEDRIVENBEANSARENEWTOTHEEJB20ARCHITECTURESUPPORTEDINTHEJ2EE13PLATFORMMESSAGEDRIVENBEANSARECOMPONENTSTHATPROCESSASYNCHRONOUSMESSAGESDELIVEREDVIATHEJAVAMESSAGESERVICEJMSAPIMESSAGEDRIVENBEANS,BYIMPLEMENTINGAJMSMESSAGELISTENERINTERFACE,CANASYNCHRONOUSLYCONSUMEMESSAGESSENTTOAMQUEUEORTOPICLATERSECTIONSOFTHISCHAPTERDISCUSSEACHTYPEOFENTERPRISEBEANINDETAILENTERPRISEBEANSLIVEINSIDEEJBCONTAINERS,WHICHPROVIDELIFECYCLEMANAGEMENT,TRANSACTIONS,SECURITY,PERSISTENCE,ANDAVARIETYOFOTHERSERVICESFORTHEMANEJBCONTAINERISPARTOFANEJBSERVER,WHICHPROVIDESNAMINGANDDIRECTORYSERVICES,EMAILSERVICES,ANDSOONWHENACLIENTINVOKESANOPERATIONONANENTERPRISEBEAN,THECALLISINTERCEPTEDBYITSCONTAINERBYINTERPOSINGBETWEENCLIENTSANDCOMPONENTSATTHEMETHODCALLLEVEL,CONTAINERSCANINJECTSERVICESTHATPROPAGATEACROSSCALLSANDCOMPONENTS,ANDEVENACROSSCONTAINERSRUNNINGONDIFFERENTSERVERSANDDIFFERENTMACHINESBECAUSETHECONTAINERADDSTHESESERVICES“BEHINDTHESCENES,“THISMECHANISMSIMPLIFIESDEVELOPMENTOFBOTHCOMPONENTSANDCLIENTS521ENTERPRISEBEANSANDEJBCONTAINERSTHEEJBARCHITECTUREENDOWSENTERPRISEBEANSANDEJBCONTAINERSWITHANUMBEROFUNIQUEFEATURESTHATENABLEPORTABILITY,REUSABILITY,ANDEASEOFUSEENTERPRISEBEANINSTANCESARECREATEDANDMANAGEDATRUNTIMEBYACONTAINERIFANENTERPRISEBEANUSESONLYTHESERVICESDEFINEDBYTHEEJBSPECIFICATION,THEENTERPRISEBEANCANBEDEPLOYEDINANYCOMPLIANTEJBCONTAINERSPECIALZEDCONTAINERSCANPROVIDEADDITIONALSERVICESBEYONDTHOSEDEFINEDBYTHEEJBSPECIFICATIONANENTERPRISEBEANTHATDEPENDSONSUCHASERVICECANBEDEPLOYEDONLYINACONTAINERTHATSUPPORTSTHATSERVICETHEBEHAVIOROFANENTERPRISEBEANISNOTWHOLLYCONTAINEDINITSIMPLEMENTATIONSERVICEINFORMATION,INCLUDINGTRANSACTIONINFORMATIONDESCRIBEDINCHAPTER8ANDSECURITYINFORMATIONDESCRIBEDINCHAPTER9,ISSEPARATEFROMTHEENTERPRISEBEANIMPLEMENTATIONFORTRANSACTIONS,THISSEPARATIONISPARTICULARLYTRUEWHENTHEBEANOPTSTODELEGATETRANSACTIONMANAGEMENTTOTHECONTAINERHOWEVER,BEANSTHATCHOOSETODOTHEIROWNTRANSACTIONMANAGEMENTINCLUDECALLSTOTHEAPPROPRIATEMETHODSOFTHEJAVATRANSACTIONUSERTRANSACTIONINTERFACEINTHEIRIMPLEMENTACTIONWHENSERVICEINFORMATIONISKEPTSEPARATEFROMTHEBEANIMPLEMENTATION,THESERVICEINFORMATIONCANBECUSTOMIZEDDURINGAPPLICATIONASSEMBLYANDDEPLOYMENTDESCRIBEDINCHAPTER7THISMAKESITPOSSIBLETOINCLUDEANENTERPRISEBEANINANASSEMBLEDAPPLICATIONWITHOUTREQUIRINGSOURCECODECHANGESORRECOMPILATION,EVENWHENITISREDEPLOYEDINADIFFERENTENVIRONMENTSPECIFYINGSERVICELEVELDETAILSINTHEDEPLOYMENTDESCRIPTORALSOGREAT1YREDUCESTHEAMOUNTOFCODETHATADEVELOPERNEEDSTOWRITE中文翻译JAVABEAN的发展在J2EE的多层应用中，企业的JAVABEANS（EJB）三层主机应用审议具体的业务逻辑，并提供系统级的服务，如交易管理，并且同时起到控制性和安全性。ENTERPRISEJAVABEANS技术提供了一个分布式组件模型，使开发人员能够专注于解决业务问题，而依靠J2EE平台，可以处理复杂系统的层次问题。这一关系的分离，使其快速发展的容易性，更方便，严谨的，且具有很强的安全应用。在J2EE编程模型中，EJB的组件再表达和构成中起到连接的作用，并且由由WEB层和业务关键数据和系统保持在企业信息系统三层。这一章描述了观念，以中央企业JAVABEANS的构成并提供指导方针和建议，以最佳方式使用EJB的复合部件。该章审查的性质，业务逻辑，以及描述的问题，开发者需要解决的时候，执行业务逻辑描述了组件模型并且企业JAVABEANS技术架构提供了解决这些问题的描述了远程和本地客户的意见详细说明了对三种类型的企业BEANS，实体BEANS，会议BEANS和消息驱动BEANS建议设计指引开发的EJB组件和应用程序提出的建议和做法，以最佳利用EJB的三层所提供的服务，J2EE平台提供指引，以方便应用程序的可移植性51商业逻辑和商业对象业务逻辑，在一个很广泛的意义上来说，是一套程序或方法，用来管理特定业务功能。以面向对象的方式，使开发单位分解业务功能整合出一套组件或元素称为商业对象。像其他对象，商业对象有两种形态（或数据）和行为。举例来说，一名雇员对象的资料，如姓名，地址，社会安全号码等。他被指派到一个新的部门或改变其薪金由一个特定的百分比。以商业管理的问题，你必须描绘出商业对象的功能和相互作用，以提供理想的功能。这套企业的特殊规则，有利于找出企业对象的结构与性能，并且会随着之前的一起被当一个物体受到了其行为给其他物体在该系统中，被称为商业逻辑。以下讨论了如何界定的结构和行为，为一个业务对象，他设计到所施加的规定以及商业问题。举例来说，样品应用软件使用的一组业务对象目录对象，以查看可用的对象购物车反对暂时搁置客户的选择对象一个账户对象为一个客户保存资讯明确的制定对象放置的顺序使用该账户的对象，以此为例，其规定包括1每个客户必须有一个独一无二的账号。2每一个账户应该有联系信息，为保护客户的详细信息如姓名，街道地址和电子邮件地址。3客户必须能够创造新的账户和关闭（或删除）账户。4客户必须能够更新他们的账户联系资料。5客户必须能够检索他们的账户信息。6客户只可以检索和更新他们自己的账户信息。7该账户资料必须保持持久性存储。8多个客户必须能够再同一时间进入他们的账户资料。9多个用户不能同时更新同一个账户的信息第一点前两项指明了账户对象的结构和属性遵循这些规则，该账户的对象应该有一个外地使用账户认证和其他几个领域进行详细地址，电话，以及其他联系信息。该账户的重要的目的描述和要求再34和5举例来说账户应该有方法，来创建一个新账户，以更新联系资料，并获得账户资料最后四项指明要求一般必须满足的条件，使该账户的对象都可以妥善地履行其功能。举例来说，当一个客户端更新一个账户，客户应被批准访问特定账户，并更新账户资料，应以书面向持久性存储。没有其他客户应能获得特定账户兼任。类似的分析和定义要求可表现为其他物体。举例来说，一个命令对象都有一套条件对自己的行为有显着相关性，以行为的一个账户对象。这就是，客户需要得到授权之前，更新或读的状况，一声令下，为了细节需要被写入到一个持久存储，等等。如果你审视商业对象公司在类似的申请，你会看到即使实际结构及行为和对象是有密切联系的业务性问题，最后是如何解决。有许多服务和这些业务对象提供后续的具体模式，是相当的通用。511商业对象的共同需求本节叙述共同要求的商业对象公司。5111维持状态业务对象往往需要保持状态之间的方法调用。这种状况可以是会话或持久性。会话状态，是状态的主要开发，在某个物体上在交谈之间，客户与应用。持久化状态，是状态储存在数据库或其他持久性存储和会话在客户与应用之间。了解持久状态，考虑一个账户对象。当用户创建一个账户，账户资料须永久保存，使当用户退出应用，并重新进入申请时，账户信息可以提交给用户。状态的一个账户对象需要保持在持久存储空间，例如一个数据库。5112共享操作上的数据另一个共同特点是商业对象，他们经常运作共享数据。在这种情况下，必须采取措施，以提供并发控制和适当程度的隔离接入到共享数据。的一个例子，这种设想将多个用户更新同一账户信息。如果两个用户试图更新同一账户在同一时间内，一个机制，必须用来保持数据的一致状态。5113参与交易一项交易，可以说是一套任务需要完成作为一个单位。如果其中一项任务失败了，所有的任务，在单位将回滚。如果他们全部成功，这项交易表示，将要发生。商业对象公司往往需要参与交易。举例来说，为了布置需求加以交易，因为该集的任务需要完成一项命令消耗的数量，所购的项目清单，储存命令细节，并发送订单确认信给使用者。对于这笔交易完成后，所有这些工作都必须成功。如果任何一个这些任务失败的话，所做的工作等各项工作都需要还原的。在许多业务中交易可跨一个以上的远程数据源。这种交易的所谓分布式交易需要特别议定书，以确保数据的完整性。第8章讨论所涉及的问题中的应用行动管理。5114大批客户的服务业务对象应能提供其服务，以大量的客户在同一时间举行。这种转化的要求，例如管理算法，让每个客户有一个印象，就是一个专门的业务对象是有利于服务。其请求如果没有这样一个管理机制，系统会消耗所有资源和将不能够服务更多的客户。5115继续提供给客户业务对象继续提供给客户时，甚至系统崩溃，服务被称为高可用性。该EJB容器中为一名业务对象居住地提供这项服务，利用策略，以掩盖各种服务器错误给客户。5116提供远程访问数据委托人应当能够远程接入服务提供的一个业务对象。这就是说，业务对象应该有某种类型的基础设施，以支持服务的客户网络。这反过来又意味着一个商业对象应该是一种分布式计算环境中，充分照顾到基本的问题，在分布式系统，如定位和失败的透明度。5117控制访问所提供的服务，商业对象公司往往需要某种类型的客户端认证和授权机制，使只有某一套客户机访问保护服务。举例来说，它应核实客户的授权更新账户信息，在一个账户业务对象，才准许它做的事如此。在许多企业的情况，不同级别的访问控制是必要的。举例来说，员工应该只允许查看自己的工资物体，而一个发薪管理员可以查看以及修改一切薪金物体。5118再度使用一个共同的要求，商业对象的是他们可重复使用不同的组成部分，同时应用和/或不同的应用程序。举例来说，一个应用软件，用于由发薪部门，以跟踪数据库员工表中的薪金可能有两笔生意对象雇员和薪金。月薪业务对象，可使用的服务，员工业务对象获得职雇员。申请时，可以追踪员工休假津贴可能想要使用这名雇员对象，以获取它们的名称，有关雇主通过雇员数目。他们开发的一个标准方法，并运行在一个环境中，遵守这些标准。