外文原文CHAPTER1UNDERSTANDINGTHEMESSAGINGPARADIGMCOMPUTERSANDPEOPLECANCOMMUNICATEBYUSINGMESSAGINGSYSTEMSTOEXCHANGEMESSAGESOVERELECTRONICNETWORKSTHEMOSTUBIQUITOUSMESSAGINGSYSTEMTODAYISEMAIL,WHICHFACILITATESCOMMUNICATIONAMONGPEOPLEWHILEEMAILISANIMPORTANTHUMANTOHUMANMESSAGINGSYSTEM,THISBOOKISNOTABOUTEMAILINSTEAD,THISBOOKISCONCERNEDWITHMESSAGINGSYSTEMSTHATALLOWDIFFERENTSOFTWAREAPPLICATIONSTOCOMMUNICATEWITHEACHOTHERTHESEAPPLICATIONTOAPPLICATIONMESSAGINGSYSTEMS,WHENUSEDINBUSINESSSYSTEMS,AREGENERICALLYREFERREDTOASENTERPRISEMESSAGINGSYSTEMS,ORMESSAGEORIENTEDMIDDLEWAREMOMENTERPRISEMESSAGINGSYSTEMSALLOWTWOORMOREAPPLICATIONSTOEXCHANGEINFORMATIONINTHEFORMOFMESSAGESAMESSAGE,INTHISCASE,ISASELFCONTAINEDPACKAGEOFBUSINESSDATAANDNETWORKROUTINGHEADERSTHEBUSINESSDATACONTAINEDINAMESSAGECANBEANYTHINGDEPENDINGONTHEBUSINESSSCENARIOANDUSUALLYCONTAINSINFORMATIONABOUTSOMEBUSINESSTRANSACTIONINENTERPRISEMESSAGINGSYSTEMS,MESSAGESINFORMANAPPLICATIONOFSOMEEVENTOROCCURRENCEINANOTHERSYSTEMUSINGMESSAGEORIENTEDMIDDLEWARE,MESSAGESARETRANSMITTEDFROMONEAPPLICATIONTOANOTHERACROSSANETWORKMOMPRODUCTSENSURETHATMESSAGESAREPROPERLYDISTRIBUTEDAMONGAPPLICATIONSINADDITION,MOMSUSUALLYPROVIDEFAULTTOLERANCE,LOADBALANCING,SCALABILITY,ANDTRANSACTIONALSUPPORTFORENTERPRISESTHATNEEDTORELIABLYEXCHANGELARGEQUANTITIESOFMESSAGESMOMVENDORSUSEDIFFERENTMESSAGEFORMATSANDNETWORKPROTOCOLSFOREXCHANGINGMESSAGES,BUTTHEBASICSEMANTICSARETHESAMEANAPIISUSEDTOCREATEAMESSAGE,GIVEITAPAYLOADAPPLICATIONDATA,ASSIGNITROUTINGINFORMATION,ANDTHENSENDTHEMESSAGETHESAMEAPIISUSEDTORECEIVEMESSAGESPRODUCEDBYOTHERAPPLICATIONSINALLMODERNENTERPRISEMESSAGINGSYSTEMS,APPLICATIONSEXCHANGEMESSAGESTHROUGHVIRTUALCHANNELSCALLEDDESTINATIONSWHENAMESSAGEISSENT,ITSADDRESSEDTOADESTINATION,NOTASPECIFICAPPLICATIONANYAPPLICATIONTHATSUBSCRIBESORREGISTERSANINTERESTINTHATDESTINATIONMAYRECEIVETHATMESSAGEINTHISWAY,THEAPPLICATIONSTHATRECEIVEMESSAGESANDTHOSETHATSENDMESSAGESAREDECOUPLEDSENDERSANDRECEIVERSARENOTBOUNDTOEACHOTHERINANYWAYANDMAYSENDANDRECEIVEMESSAGESASTHEYSEEFITALLMOMVENDORSPROVIDEAPPLICATIONDEVELOPERSWITHANAPIFORSENDINGANDRECEIVINGMESSAGESWHILEAMOMVENDORIMPLEMENTSITSOWNNETWORKINGPROTOCOLS,ROUTING,ANDADMINISTRATIONFACILITIES,THEBASICSEMANTICSOFTHEDEVELOPERAPIPROVIDEDBYDIFFERENTMOMSARETHESAMETHISSIMILARITYINAPISMAKESTHEJAVAMESSAGESERVICEPOSSIBLETHEJAVAMESSAGESERVICEJMSISAVENDORAGNOSTICJAVAAPITHATCANBEUSEDWITHMANYDIFFERENTMOMVENDORSJMSISANALOGOUSTOJDBCINTHATAPPLICATIONDEVELOPERSREUSETHESAMEAPITOACCESSMANYDIFFERENTSYSTEMSIFAVENDORPROVIDESACOMPLIANTSERVICEPROVIDERFORJMS,THENTHEJMSAPICANBEUSEDTOSENDANDRECEIVEMESSAGESTOTHATVENDORFOREXAMPLE,YOUCANUSETHESAMEJMSAPITOSENDMESSAGESUSINGPROGRESSSONICMQASYOUDOIBMSMQSERIESITISTHEPURPOSEOFTHISBOOKTOEXPLAINHOWENTERPRISEMESSAGINGSYSTEMSWORKANDINPARTICULARHOWTHEJAVAMESSAGESERVICEISUSEDWITHTHESESYSTEMSTHISBOOKFOCUSESONJMS102,THEMOSTRECENTVERSIONOFTHESPECIFICATION,WHICHWASINTRODUCEDINNOVEMBER1999THERESTOFTHISCHAPTEREXPLORESENTERPRISEMESSAGINGANDJMSINMOREDETAIL,SOTHATYOUHAVEASOLIDFOUNDATIONWITHWHICHTOLEARNABOUTTHEJMSAPIANDMESSAGINGCONCEPTSINTHERESTOFTHISBOOKWEASSUMETHATYOUAREALREADYFAMILIARWITHTHEJAVAPROGRAMMINGLANGUAGEOTHERTHANTHAT,EVERYTHINGISEXPLAINED11ENTERPRISEMESSAGINGENTERPRISEMESSAGINGISNOTANEWCONCEPTMESSAGINGPRODUCTSSUCHASIBMMQSERIES,MICROSOFTMSMQ,TIBCORENDEVOUS,OPENHORIZONAMBROSIA,ANDMODULUSINTERAGENTHAVEBEENINEXISTENCEFORMANYYEARSNEWERMESSAGINGPRODUCTSSUCHASPROGRESSSONICMQ,SOFTWIREDIBUS,ANDFIORANOMQHAVEBEENBUILTFROMTHEGROUNDUP,BASEDONTHENEEDFORDOINGRELIABLEBUSINESSTOBUSINESSCOMMUNICATIONSOVERTHEINTERNETAKEYCONCEPTOFENTERPRISEMESSAGINGISMESSAGESAREDELIVEREDASYNCHRONOUSLYFROMONESYSTEMTOOTHERSOVERANETWORKTODELIVERAMESSAGEASYNCHRONOUSLYMEANSTHESENDERISNOTREQUIREDTOWAITFORTHEMESSAGETOBERECEIVEDORHANDLEDBYTHERECIPIENTITISFREETOSENDTHEMESSAGEANDCONTINUEPROCESSINGASYNCHRONOUSMESSAGESARETREATEDASAUTONOMOUSUNITSEACHMESSAGEISSELFCONTAINEDANDCARRIESALLOFTHEDATAANDSTATENEEDEDBYTHEBUSINESSLOGICTHATPROCESSESITINASYNCHRONOUSMESSAGING,APPLICATIONSUSEASIMPLEAPITOCONSTRUCTAMESSAGE,THENHANDITOFFTOTHEMESSAGEORIENTEDMIDDLEWAREFORDELIVERYTOONEORMOREINTENDEDRECIPIENTSFIGURE11AMESSAGEISAPACKAGEOFBUSINESSDATATHATISSENTFROMONEAPPLICATIONTOANOTHEROVERTHENETWORKTHEMESSAGESHOULDBESELFDESCRIBINGINTHATITSHOULDCONTAINALLTHENECESSARYCONTEXTTOALLOWTHERECIPIENTSTOCARRYOUTTHEIRWORKINDEPENDENTLYFIGURE11MESSAGEORIENTEDMIDDLEWAREMESSAGEORIENTEDMIDDLEWAREARCHITECTURESOFTODAYVARYINTHEIRIMPLEMENTATIONTHESPECTRUMRANGESFROMACENTRALIZEDARCHITECTURETHATDEPENDSONAMESSAGESERVERTOPERFORMROUTING,TOADECENTRALIZEDARCHITECTURETHATDISTRIBUTESTHE“SERVER“PROCESSINGOUTTOTHECLIENTMACHINESAVARIEDARRAYOFPROTOCOLSINCLUDINGTCP/IP,HTTP,SSL,ANDIPMULTICASTAREEMPLOYEDATTHENETWORKTRANSPORTLAYERSOMEMESSAGINGPRODUCTSUSEAHYBRIDOFBOTHAPPROACHES,DEPENDINGONTHEUSAGEMODELBEFOREWEDISCUSSTHEDIFFERENTARCHITECTURES,ITISIMPORTANTTOEXPLAINWHATWEMEANBYTHETERMCLIENTMESSAGINGSYSTEMSARECOMPOSEDOFMESSAGINGCLIENTSANDSOMEKINDOFMOMTHECLIENTSSENDMESSAGESTOTHEMOM,WHICHTHENDISTRIBUTESTHOSEMESSAGESTOOTHERCLIENTSTHECLIENTISABUSINESSAPPLICATIONORCOMPONENTTHATISUSINGTHEMESSAGINGAPIINOURCASEJMS111CENTRALIZEDARCHITECTURESENTERPRISEMESSAGINGSYSTEMSTHATUSEACENTRALIZEDARCHITECTURERELYONAMESSAGESERVERAMESSAGESERVER,ALSOCALLEDAMESSAGEROUTERORBROKER,ISRESPONSIBLEFORDELIVERINGMESSAGESFROMONEMESSAGINGCLIENTTOOTHERMESSAGINGCLIENTSTHEMESSAGESERVERDECOUPLESASENDINGCLIENTFROMOTHERRECEIVINGCLIENTSCLIENTSONLYSEETHEMESSAGINGSERVER,NOTOTHERCLIENTS,WHICHALLOWSCLIENTSTOBEADDEDANDREMOVEDWITHOUTIMPACTINGTHESYSTEMASAWHOLETYPICALLY,ACENTRALIZEDARCHITECTUREUSESAHUBANDSPOKETOPOLOGYINASIMPLECASE,THEREISACENTRALIZEDMESSAGESERVERANDALLCLIENTSCONNECTTOITASSHOWNINFIGURE12,THEHUBANDSPOKEARCHITECTURELENDSITSELFTOAMINIMALAMOUNTOFNETWORKCONNECTIONSWHILESTILLALLOWINGANYPARTOFTHESYSTEMTOCOMMUNICATEWITHANYOTHERPARTOFTHESYSTEMFIGURE12CENTRALIZEDHUBANDSPOKEARCHITECTUREINPRACTICE,THECENTRALIZEDMESSAGESERVERMAYBEACLUSTEROFDISTRIBUTEDSERVERSOPERATINGASALOGICALUNIT112DECENTRALIZEDARCHITECTURESALLDECENTRALIZEDARCHITECTURESCURRENTLYUSEIPMULTICASTATTHENETWORKLEVELAMESSAGINGSYSTEMBASEDONMULTICASTINGHASNOCENTRALIZEDSERVERSOMEOFTHESERVERFUNCTIONALITYPERSISTENCE,TRANSACTIONS,SECURITYISEMBEDDEDASALOCALPARTOFTHECLIENT,WHILEMESSAGEROUTINGISDELEGATEDTOTHENETWORKLAYERBYUSINGTHEIPMULTICASTPROTOCOLIPMULTICASTALLOWSAPPLICATIONSTOJOINONEORMOREIPMULTICASTGROUPSEACHGROUPUSESANIPNETWORKADDRESSTHATWILLREDISTRIBUTEANYMESSAGESITRECEIVESTOALLMEMBERSINITSGROUPINTHISWAY,APPLICATIONSCANSENDMESSAGESTOANIPMULTICASTADDRESSANDEXPECTTHENETWORKLAYERTOREDISTRIBUTETHEMESSAGESAPPROPRIATELYSEEFIGURE13UNLIKEACENTRALIZEDARCHITECTURE,ADISTRIBUTEDARCHITECTUREDOESNTREQUIREASERVERFORTHEPURPOSESOFROUTINGMESSAGESTHENETWORKHANDLESROUTINGAUTOMATICALLYHOWEVER,OTHERSERVERLIKEFUNCTIONALITYISSTILLREQUIREDTOBEINCLUDEDWITHEACHCLIENT,SUCHASMESSAGEPERSISTENCEANDMESSAGEDELIVERYSEMANTICSLIKEONCEANDONLYONCEDELIVERYFIGURE13DECENTRALIZEDIPMULTICASTARCHITECTURE113HYBRIDARCHITECTURESADECENTRALIZEDARCHITECTUREUSUALLYIMPLIESTHATANIPMULTICASTPROTOCOLISBEINGUSEDACENTRALIZEDARCHITECTUREUSUALLYIMPLIESTHATTHETCP/IPPROTOCOLISTHEBASISFORCOMMUNICATIONBETWEENTHEVARIOUSCOMPONENTSAMESSAGINGVENDORSARCHITECTUREMAYALSOCOMBINETHETWOAPPROACHESCLIENTSMAYCONNECTTOADAEMONPROCESSUSINGTCP/IP,WHICHINTURNCOMMUNICATEWITHOTHERDAEMONPROCESSESUSINGIPMULTICASTGROUPS114CENTRALIZEDARCHITECTUREASAMODELBOTHENDSOFTHEDECENTRALIZEDANDCENTRALIZEDARCHITECTURESPECTRUMHAVETHEIRPLACEINENTERPRISEMESSAGINGTHEADVANTAGESANDDISADVANTAGESOFDISTRIBUTEDVERSUSCENTRALIZEDARCHITECTURESAREDISCUSSEDINMOREDETAILINCHAPTER7INTHEMEANTIMEWENEEDACOMMONMODELFORDISCUSSINGOTHERASPECTSOFENTERPRISEMESSAGINGINORDERTOSIMPLIFYDISCUSSIONS,THISBOOKUSESACENTRALIZEDARCHITECTUREASALOGICALVIEWOFENTERPRISEMESSAGINGTHISISFORCONVENIENCEONLYANDISNOTANENDORSEMENTOFCENTRALIZEDOVERDECENTRALIZEDARCHITECTURESTHETERM“MESSAGESERVER“ISFREQUENTLYUSEDINTHISBOOKTOREFERTOTHEUNDERLYINGARCHITECTURETHATISRESPONSIBLEFORROUTINGANDDISTRIBUTINGMESSAGESINCENTRALIZEDARCHITECTURES,THEMESSAGESERVERISAMIDDLEWARESERVERORCLUSTEROFSERVERSINDECENTRALIZEDARCHITECTURES,THESERVERREFERSTOTHELOCALSERVERLIKEFACILITIESOFTHECLIENT12THEJAVAMESSAGESERVICEJMSTHEJAVAMESSAGESERVICEJMSISANAPIFORENTERPRISEMESSAGINGCREATEDBYSUNMICROSYSTEMSJMSISNOTAMESSAGINGSYSTEMITSELFITSANABSTRACTIONOFTHEINTERFACESANDCLASSESNEEDEDBYMESSAGINGCLIENTSWHENCOMMUNICATINGWITHMESSAGINGSYSTEMSINTHESAMEWAYTHATJDBCABSTRACTSACCESSTORELATIONALDATABASESANDJNDIABSTRACTSACCESSTONAMINGANDDIRECTORYSERVICES,JMSABSTRACTSACCESSTOMOMSUSINGJMS,AMESSAGINGAPPLICATIONSMESSAGINGCLIENTSAREPORTABLEACROSSMOMPRODUCTSTHECREATIONOFJMSWASANINDUSTRYEFFORTJAVASOFTTOOKTHELEADONTHESPECANDWORKEDVERYCLOSELYWITHTHEMESSAGINGVENDORSTHROUGHOUTTHEPROCESSTHEINITIALOBJECTIVEWASTOPROVIDEAJAVAAPIFORCONNECTIVITYTOMOMSYSTEMSHOWEVER,THISCHANGEDTOTHEWIDEROBJECTIVEOFSUPPORTINGMESSAGINGASAFIRSTCLASSJAVADISTRIBUTEDCOMPUTINGPARADIGMEQUALLYWITHREMOTEPROCEDURECALLRPCBASEDSYSTEMSLIKECORBAANDENTERPRISEJAVABEANSTHEREWEREANUMBEROFMOMVENDORSTHATPARTICIPATEDINTHECREATIONOFJMSITWASANINDUSTRYEFFORTRATHERTHANASUNEFFORTSUNWASTHESPECLEADANDDIDSHEPHERDTHEWORKBUTITWOULDNOTHAVEBEENSUCCESSFULWITHOUTTHEDIRECTINVOLVEMENTOFTHEMESSAGINGVENDORSALTHOUGHOURORIGINALOBJECTIVEWASTOPROVIDEAJAVAAPIFORCONNECTIVITYTOMOMSYSTEMS,THISCHANGEDOVERTHECOURSEOFTHEWORKTOABROADEROBJECTIVEOFSUPPORTINGMESSAGINGASAFIRSTCLASSJAVADISTRIBUTEDCOMPUTINGPARADIGMONEQUALFOOTINGWITHRPCMARKHAPNER,JMSSPECLEAD,SUNMICROSYSTEMSTHERESULTISABESTOFBREED,ROBUSTSPECIFICATIONTHATINCLUDESARICHSETOFMESSAGEDELIVERYSEMANTICS,COMBINEDWITHASIMPLEYETFLEXIBLEAPIFORINCORPORATINGMESSAGINGINTOAPPLICATIONSTHEINTENTWASTHATINADDITIONTONEWVENDORS,EXISTINGMESSAGINGVENDORSWOULDSUPPORTTHEJMSAPI121JMSMESSAGINGMODELSPUBLISHANDSUBSCRIBEANDPOINTTOPOINTJMSPROVIDESFORTWOTYPESOFMESSAGINGMODELS,PUBLISHANDSUBSCRIBEANDPOINTTOPOINTQUEUINGTHEJMSSPECIFICATIONREFERSTOTHESEASMESSAGINGDOMAINSINJMSTERMINOLOGY,PUBLISHANDSUBSCRIBEANDPOINTTOPOINTAREFREQUENTLYSHORTENEDTOPUB/SUBANDP2PORPTP,RESPECTIVELYTHISBOOKUSESBOTHTHELONGANDSHORTFORMSTHROUGHOUTINTHESIMPLESTSENSE,PUBLISHANDSUBSCRIBEISINTENDEDFORAONETOMANYBROADCASTOFMESSAGES,WHILEPOINTTOPOINTISINTENDEDFORONETOONEDEL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(jīng)沒有集中的服務(wù)器。一些服務(wù)器功能（持續(xù)性，交易，安全）是嵌入式，作為當?shù)氐囊徊糠挚蛻?，而消息路由是下放給網(wǎng)絡(luò)層采用IP組播協(xié)議的。IP組播允許申請加入一個或多個組播組，每組用一個IP網(wǎng)絡(luò)地址重新分配訊息，它收到的所有成員都在其集團。這樣，應(yīng)用程序可以發(fā)送短信到一個IP組播地址，并期望網(wǎng)絡(luò)層重新分配訊息適度，不像一個集中架構(gòu)，這是一種分布式體系結(jié)構(gòu)并不需要一臺服務(wù)器用于路由信息網(wǎng)絡(luò)處理路由是自動的。（見圖三）不過，與其他服務(wù)器的功能一樣，還需要包括每一個客戶，如信息，持續(xù)性和信息傳送語義一次對一次地交付。圖13113混合結(jié)構(gòu)一個分散的體系結(jié)構(gòu)通常意味著一個IP組播協(xié)議被使用。集中式體系結(jié)構(gòu)通常意味著TCP/IP協(xié)議是基礎(chǔ)，從而溝通各種組件。一個信息供應(yīng)商的架構(gòu)也可以結(jié)合兩種辦法?？蛻粢部梢酝瑫r連接到一個守護進程過程中使用TCP/IP，而這又與其他的DAEMON進程利用IP多播組相聯(lián)系。114集中式體系結(jié)構(gòu)作為范本在企業(yè)消息中，兩端的分散與集中的架構(gòu)組播有其各自的位置。在第7章中，更詳細地討論了關(guān)于優(yōu)點和缺點分布式相對于集中式的架構(gòu)。在此期間，我們需要有一個共同的模式，旨在討論其他方面的企業(yè)消息。為了簡化討論，這本書采用了集中式體系結(jié)