服務(wù)器應(yīng)用程序中英文對(duì)照外文翻譯文獻(xiàn)

服務(wù)器應(yīng)用程序中英文對(duì)照外文翻譯文獻(xiàn)PAGEPAGE1服務(wù)器應(yīng)用程序中英文對(duì)照外文翻譯文獻(xiàn)(文檔含英文原文和中文翻譯)ApplicationofPowerBuilderUserObjectsinDevelopingDistributedPrograms0IntroductionTheobject-orientedmethodsandtoolshavebeenrecommendedindevelopingsoftware.TheUserobjectofPowerBuildersimulatestheclassinobject-orientedconception.ItisoneofthemostflexileobjectstodeveloptheperformanceofPowerBuilder.ByusingPowerBuilder,thedevelopercandevelopthefunctionoftheprimaryobjectfunction,addnewuser-definedcomponentsandenhancethereuseofcode.Moreover,wecandevelopthecomponentbyC++toimprovethespeed-sensitiveparts,andinsertthemtothePowerBuilderprogram.TherearetwokindsofPowerBuilderobjects:oneofthemisthevisualobjects,theycanbeusedtocommunicatebetweenapplicationprogramandusers;theotherkindofthemisthenonvisualobjects,ithasnovisualcomponent,andismainlyusedtoencapsulateandcompletethecertainkindsofbusinesslogic.UserObjects——astheotherPowerBuilderobjects,containsomeofproperties,suchasevent、instancevariables、userobjectfunctionsetc.Generally,anonvisualobjectrepresentstheoneclassinsystemanalysis.Wedon'tintendtodiscusshowtodefineinstancevariablesandtowritethefunctionofuserobject,youcanreferthePowerBuilderdocuments.Usuallyweusenon-visualobjecttoperformthePowerBuilderdistributedapplication.Distributedcomputingisanaturaloutgrowthofthedevelopmentofnetworkcomputersystemsthatusetheclient/serverarchitecture.Itallowsyoutogetthemostintheclient/serverarchitecture.TheconceptionofdistributedcomputingiscloselyconnectedwithRPC(remoteprocedurecall).RPCisthetechniquethattheclientprogramcancallprocesses(functions)oftheremoteComputer,andgettheprocessresult(functionreturnvalue).PowerBuildershieldmanydetailsofRPCandmakesiteasytodeveloptheserverandtheclientapplication.1TheApplicationofUserObjectsontheServerAremoteobjectisacustomclass(nonvisual)userobjectthatiscontainedinanapplicationlocatedonaremoteserver.Eachremoteobjectisacustomclassuser(nonvisual)objectthathasbeingmentionedinthepartofuserobjectsontheremoteserverapplication,theyprovideservicetotheclient.Remoteobjectscanbeinvokedacrossprocessboundariesoracrosscomputerboundaries.Thatis,aclientapplicationcaninvokearemoteobjectassociatedwithaseparateexecutableonthesamecomputeroronanothercomputerinanetwork.Thekeystosuccessfuldistributedapplicationdevelopmentaretouseobject-orientedtechniqueandtoselectremoteobjectscarefully.PowerBuilder'supportfordistributedcomputingisalogicalextensionofitsobject-orientedarchitecture.Forthisreason,aPowerBuilderapplicationthatusesobject-orientedtechniquescanbeconvertedtoadistributedapplicationwithaminimumofdifficulty.Whenyouarereadytobegindevelopingadistributedapplication,youneedtopackageyourbusinesslogicincustomclass(nonvisual)userobjects.Customclassuserobjectsprovidethefoundationforanydistributedapplication.Onceyouhavecreatedyournonvisualobjects,youcanmaketheadjustmentsrequiredforclientapplicationstoaccesstheseobjectsremotely.Anycustomclassuserobjectcanactasaremoteobjectinaserverapplication.However,notallnonvisualobjectsaregoodcandidatesfordistributedprocessing.Sincenetworkandserverperformancecandegradeiftoomanyobjectsaredeployedinremoteservers,youneedtobeselectiveaboutwhichobjectsyoudecidetomakeremote.1.1RemoteObjectsThebasicbuildingblocksofaserverapplicationaretheremoteobjectsitcontains.Eachremoteobjectisacustomclass(nonvisual)userobjectthathasmethodsthatcanbeinvokedbyoneormoreclientapplications.Atypicalserverapplicationcontainsseveralnonvisualobjectsthatpackagebusinesslogicintoreusablecomponents.Sotheprimarytaskinbuildingaserverapplicationiswritingthemethodsforthenonvisualobjects.1.1.1InstancevariablesTheinstanceexistsinmemoryandhasvaluesassignedtoitspropertiesandvariables.1.1.2PassingbyreferenceYoucanpassargumentstocomponentmethodsbyreference.However,thebehaviorissomewhatdifferentinadistributedapplicationthaninanondistributedapplication.Whenyoupassbyreference,thevariableisactuallycopiedtotheserverbeforethemethodisexecutedandthencopiedbackwhenthemethodcompletesexecution.Thisbehaviorisusuallytransparenttotheapplication;butinsomesituationsitcanaffecttheoutcomeofprocessing.Forexample,supposeyoudefineamethodcalledincrement_valuesthattakestwoargumentscalledxandy,bothofwhicharepassedbyreference.Thescriptforthemethodincrementsxandyasshownbelow:x=x+1,y=y+1Theclientusesthefollowingcodetocallthemethod:intz,z=1increment_values(z,z)Inanondistributedapplication,thevalueofzafterthemethodcompletedexecutionwouldbe3(becausethelocalinvocationpassesapointertoz,andzisincrementedtwice).Inadistributedapplication,thevalueofzwouldbe2(becausetheremoteinvocationpassestwocopiesofz,whichareincrementedseparately).1.1.3DatatypesofreturnvaluesThemethodsassociatedwithanonvisualobjectinaserverapplicationcantakeargumentsthatusethefollowingdatatypes:standarddata、types、structures、customclass(nonvisual)userobjects.Thereturnvalueofaremoteobjectmethodcanbeofanystandarddatatype.Thereturnvaluecanalsobeacustomclass(nonvisual)userobjectorastructure,butnotanarrayofstructures.1.2SharedObjectsToallowyoutoworkwithpersistent,shareddatainadistributedapplication,PowerBuilderprovidessupportforsharedobjects.Sharedobjectsareuserobjectsthatcanbesharedbymultipleclientconnections.Atexecutiontime,Power-Buildercreatesaseparatethread(session)foreachsharedobjectinstanceandanyobjectsthatthesharedobjectcreates.Therefore,anyworkperformedinsidethesharedobjectwillruninaseparatethread.Youcanshareanycustomclass(nonvisual)userobjectyoucreate.Inaddition,youcansharemanyofthebuilt-in,nonvisualobjectsthatareavailablewithPowerBuilder,aswellasstandardclassuserobjectsthatinheritfromthesebuilt-inobjects.However,PowerBuilderdoesn'tallowyoutosharethefollowingtypesofobjects:a)DataStoreb)DynamicDescriptionAreac)DynamicStagingAread)TransactionToallowmultipleclientapplicationstoshareasingleobject,theserverapplicationperformstheseoperations:(1)InvokestheSharedObjectRegisterfunctiontoregisteranamedinstanceoftheobject.(2)InvokestheSharedObjectGetfunctiontogetanobjectinstancethatisareferencetothesharedobject.(3)InvokestheSharedObjectUnregisterfunctiontoremovetheinternalreference.TheserverapplicationdoesnotneedtoissueaCREATEstatementforthesharedobject.WhentheservercallstheSharedObjectRegisterfunction,PowerBuilderautomaticallycreatesthesharedobjectinstance.Clientapplicationscannotaccessasharedobjectdirectly.Toaccessasharedobject,aclientneedstocommunicatewitharemoteobjectthatdelegatesworktothesharedobject.Oftentheremoteobjecthasaninstancevariablethatprovidesareferencetothesharedobject.1.3ServerPushTheservercomponentofadistributedapplicationcanhandlebothsynchronousandasynchronousrequests.Whenaclientissuesasynchronouscall,theserverexecutesthefunctionimmediatelywhiletheclientwaitsuntilprocessinghascompleted.Whenaclientissuesanasynchronouscall,theserverperformstheprocessingatalaterpointintime;meanwhile,theclientcancontinuetodootherworkwhiletheserverhandlestherequest.Sotoomanysynchronouscallswillmaketheclientwaitandmaycausedeadlocksituations.Tomakeanasynchronousfunctioncall,youneedtocalltheremoteobjectfunctionwiththePOSTkeyword.Usingatechniquecalledserverpush,theservercansendmessagestotheclient.Thisisparticularlyusefulwhentheclientneedstobenotifiedofthecompletionofanasynchronousrequest.Tosendamessagetotheclient,theserverneedstoknowwhichclient-sideobjecttosendthemessageto.Therefore,theclientmustpassareferencetoanonvisualobjecttotheserver.Whentheserverreceivestheobjectreference,itautomaticallycreatesaremotereferencetotheclient-sideobjectandcallsoneormorefunctionsassociatedwiththisobject.Functioncallsmadeagainsttheremotereferencearepassedbackoverthewiretotheclientthatcontainstheobject.Toensurethatmessagesareactuallysenttotheclient-sideobject,theclientmustnotpassanautoinstantiatedobjecttotheserver.Instead,theclientmustpassareferencetoanobjectthatiscreatedwiththeCREATEstatement.2TheApplicationofUserObjectonaClientTheapplicationofuserobjectsonaclientismainlythattheclientaccessremoteobjectsonadistributedserverbyproxyobjects,aftergettheresultsfromtheserver,theclientplaytheresultattheuserinterface.Onceaconnectiontoaserverapplicationhasbeenestablished,theclientapplicationcanbeginusingtheremoteobjectsprovidedbytheserver.Theclientcancallfunctionsassociatedwiththeremoteobjectsandaccesstheobjects'instancevariables.YoucansimplycreatetheremoteobjectdirectlybycallingtheCreateInstancefunctionoftheConnectionobject.Whenyoudeployaremoteobject'sclassdefinitioninaclientapplication,thedefinitionontheclienthasthesamenameastheremoteobjectdefinitiondeployedintheserverapplication.Variablesdeclaredwiththisobjecttypecanholdareferencetoalocalobjectinstanceoraremoteobjectinstance.Inaddition,client-sidescriptsthatusetheobjectdonotneedtoknowwheretheobjectwascreated.AfterinvokingtheCreateInstancefunctionsuccessfully,theserverwillbuildanewobjectintheclientcommissionoftheserver'smemoryinsteadoftheserverapplication'smainsession.Sootherclientscan'taccessit.2.1DefineProxyObjectEachremoteobjectcontainedinaserverapplicationhasacorrespondingclassdefinitionintheclientapplication.Theclassdefinitionontheclientcancontainthecompleteimplementationoftheremoteobject,orsimplyaProxyobjectthatprovidesarepresentationoftheremoteobject'sinterface.Ineithercase,youcanaccessremoteobjectsonadistributedserver.However,onlytheProxyobjectisrequiredontheclientfordistributedprocessing.BydeployingProxyobjectsinyourclientapplications,youcanreducethesizeofyourclientsandalsoaddalayerofsecuritybypreventingtheclientsfromaccessingsensitivebusinessalgorithms.Todefineaproxyobject,youneedtousetheproxyobjectgenerator,whichisavailableintheProjectpainter.2.2InvokingRemoteObjectFunctionsHere,weissueanasynchronouscallwiththePostkeyword,theserveraddstherequesttoaqueueandperformstheprocessingatalaterpointintime;meanwhile,theclientcancontinuetodootherworkwhiletheserverhandlestherequest.2.3DestroyingtheObjectInstanceAfteryou'vefinishedusingaremoteobject,youcanexplicitlydestroytheobjectbyusingtheDESTROYstatement,oryoucanletPowerBuilder'sgarbagecollectionfacilitycleartheobjectoutofmemoryforyouautomatically.3ConclusionUserObjectsarethebasementindevelopingdistributedPowerBuilderapplications.Ifwewanttodevelopahighquantityapplication,wemustmastertheuserobjectsindistributedapplication.PowerBuilder的用戶對(duì)象在開(kāi)發(fā)分布式程序中的應(yīng)用0引言面向?qū)ο蟮姆椒ê凸ぞ哕浖呀?jīng)在發(fā)展中國(guó)家提出并廣受歡迎。PowerBuilder用戶對(duì)象的模擬類(lèi)是面向?qū)ο蟮母拍睿@是PowerBuilder的發(fā)展表現(xiàn)最柔韌的對(duì)象之一。開(kāi)發(fā)人員可以使用PowerBuilder開(kāi)發(fā)的主要對(duì)象功能，添加新的用戶定義的組件和提高代碼的重用。此外，我們可以開(kāi)發(fā)C++來(lái)提高組件速度敏感的部位，并導(dǎo)入它們?cè)赑owerBuilder中的程序。有兩種PowerBuilder對(duì)象：其中之一是可視對(duì)象，它們可以用于應(yīng)用程序和用戶之間的溝通；它們的另一種是不可視的物體，它具有不可視組件，主要用于封裝完成某些種類(lèi)的業(yè)務(wù)邏輯。用戶對(duì)象——其他PowerBuilder對(duì)象，包含一些屬性，如事件，實(shí)例變量，用戶對(duì)象等功能。一般來(lái)說(shuō)，一個(gè)不可視對(duì)象代表了系統(tǒng)的分析類(lèi)。我們不打算討論如何定義實(shí)例變量和編寫(xiě)用戶對(duì)象的功能，您可以參考PowerBuilder的文件。通常我們使用的非可視化對(duì)象執(zhí)行PowerBuilder的分布式應(yīng)用程序。分布式計(jì)算是一個(gè)使用的客戶機(jī)/服務(wù)器架構(gòu)的網(wǎng)絡(luò)計(jì)算機(jī)系統(tǒng)的發(fā)展的自然產(chǎn)物。它可以讓你得到客戶機(jī)/服務(wù)器架構(gòu)。分布式計(jì)算的概念是緊密相連的RPC（遠(yuǎn)程過(guò)程調(diào)用）。RPC是技術(shù)，客戶端程序可以調(diào)用遠(yuǎn)程進(jìn)程（功能）計(jì)算機(jī)，并得到處理結(jié)果（函數(shù)的返回值）。PowerBuilder保護(hù)RPC的許多細(xì)節(jié)并可以很容易地開(kāi)發(fā)服務(wù)器和客戶端應(yīng)用程序。1在服務(wù)器上的應(yīng)用，用戶對(duì)象一個(gè)遠(yuǎn)程對(duì)象是一個(gè)自定義類(lèi)（非可視）在位于遠(yuǎn)程服務(wù)器上的應(yīng)用程序中的用戶對(duì)象。每個(gè)遠(yuǎn)程對(duì)象是一個(gè)自定義類(lèi)用戶（非可視），已被提到，在用戶對(duì)象的遠(yuǎn)程服務(wù)器上的應(yīng)用程序的一部分，他們的客戶提供服務(wù)的對(duì)象?？梢哉{(diào)用遠(yuǎn)程對(duì)象的跨進(jìn)程，跨計(jì)算機(jī)邊界。也就是說(shuō)，客戶端應(yīng)用程序可以調(diào)用遠(yuǎn)程對(duì)象與同一臺(tái)計(jì)算機(jī)上或在網(wǎng)絡(luò)的另一臺(tái)計(jì)算機(jī)上的單獨(dú)的可執(zhí)行文件。成功的分布式應(yīng)用開(kāi)發(fā)的關(guān)鍵是使用面向?qū)ο蠹夹g(shù)和精心選擇的遠(yuǎn)程對(duì)象。PowerBuilder的分布式計(jì)算的支持是它的對(duì)象導(dǎo)向架構(gòu)的一個(gè)合乎邏輯的延伸。出于這個(gè)原因，使用面向?qū)ο蠹夹g(shù)的一個(gè)PowerBuilder應(yīng)用程序可以轉(zhuǎn)換為以最小的分布式應(yīng)用程序難度。當(dāng)您準(zhǔn)備開(kāi)始開(kāi)發(fā)分布式應(yīng)用程序，你需要到你的業(yè)務(wù)邏輯封裝在自定義類(lèi)（非可視）用戶對(duì)象。定制類(lèi)用戶對(duì)象提供任何分布式應(yīng)用的基礎(chǔ)。一旦你創(chuàng)建了你的不可視對(duì)象，可以使客戶端應(yīng)用程序所需的遠(yuǎn)程訪問(wèn)這些對(duì)象的調(diào)整。任何自定義類(lèi)用戶對(duì)象可以作為一個(gè)服務(wù)器應(yīng)用程序的遠(yuǎn)程對(duì)象。然而，并不是所有的非可視化對(duì)象都是分布式處理的很好的候選人。由于網(wǎng)絡(luò)和服務(wù)器的性能，可以降低部署在遠(yuǎn)程服務(wù)器上，如果太多的對(duì)象，你需要有選擇性的來(lái)決定進(jìn)行遠(yuǎn)程的對(duì)象。1.1遠(yuǎn)程對(duì)象服務(wù)器應(yīng)用程序的基本構(gòu)件是它所包含的遠(yuǎn)程對(duì)象。每個(gè)遠(yuǎn)程對(duì)象是一個(gè)自定義類(lèi)（非可視）用戶對(duì)象，可以由一個(gè)或多個(gè)客戶端應(yīng)用程序調(diào)用的方法。一個(gè)典型的服務(wù)器應(yīng)用程序包含了幾個(gè)業(yè)務(wù)邏輯封裝成可重用的組件不可視對(duì)象。因此，建立一個(gè)服務(wù)器應(yīng)用程序的首要任務(wù)是寫(xiě)出非可視化對(duì)象的方法。1.1.1實(shí)例變量實(shí)例存在于內(nèi)存中，并分配給其應(yīng)有的關(guān)系和變量的值。1.1.2通過(guò)引用傳遞你可以傳遞參數(shù)參考組件的方法。然而，比在非分布式的應(yīng)用程序，在分布式應(yīng)用程序的行為是有點(diǎn)不同。當(dāng)你通過(guò)引用傳遞，變量實(shí)際上是復(fù)制到服務(wù)器的方法執(zhí)行之前，然后復(fù)制回當(dāng)該方法完成執(zhí)行。這種行為通常是透明的應(yīng)用程序，但在某些情況下，它可以影響處理結(jié)果。例如，假設(shè)你定義increment_值的方法，稱為X和Y兩個(gè)參數(shù)，這兩者都是通過(guò)引用傳遞。方法增量x和y，顯示為如下的腳本：X=X+Y=Y+1客戶端使用下面的代碼來(lái)調(diào)用該方法：整型Z，Z=1遞增值（Z，Z）在非分布式的應(yīng)用程序，完成后的z值的方法，將執(zhí)行3（因?yàn)楸镜卣{(diào)用傳遞一個(gè)指針到z，z是遞增的兩倍）。在分布式應(yīng)用程序，z的值是2（因?yàn)檫h(yuǎn)程調(diào)用傳遞z的兩個(gè)副本，分別遞增）。1.1.3數(shù)據(jù)類(lèi)型的返回值在服務(wù)器應(yīng)用程序的非可視化對(duì)象的方法可以使用??下列數(shù)據(jù)類(lèi)型：標(biāo)準(zhǔn)的數(shù)據(jù)，類(lèi)型，結(jié)構(gòu)，自定義類(lèi)（非可視）用戶對(duì)象的參數(shù)。一個(gè)遠(yuǎn)程對(duì)象的方法的返回值可以是任何類(lèi)型的標(biāo)準(zhǔn)數(shù)據(jù)。返回值也可以是自定義類(lèi)（非可視）用戶對(duì)象或結(jié)構(gòu)，而不是一個(gè)結(jié)構(gòu)數(shù)組。1.2共享對(duì)象為了讓您的工作充滿執(zhí)著，在分布式應(yīng)用程序共享數(shù)據(jù)，PowerBuilder提供了對(duì)共享對(duì)象的支持。共享對(duì)象是用戶共享的對(duì)象，可以由多個(gè)客戶端連接離子。電力建設(shè)者在執(zhí)行時(shí)，為每個(gè)共享對(duì)象實(shí)例和共享對(duì)象創(chuàng)建的任何對(duì)象創(chuàng)建一個(gè)單獨(dú)的線程（會(huì)話）。因此，里面的共享對(duì)象進(jìn)行的任何工作將運(yùn)行在一個(gè)單獨(dú)的線程。你可以分享任何自定義類(lèi)（非可視）用戶對(duì)象創(chuàng)建。此外，您可以共享許多內(nèi)置的，這是與PowerBuilder的，以及標(biāo)準(zhǔn)類(lèi)用戶對(duì)象繼承這些內(nèi)置對(duì)象的非可視化對(duì)象。然而，PowerBuilder中不允許你分享以下類(lèi)型的對(duì)象：A）數(shù)據(jù)存儲(chǔ)B）動(dòng)態(tài)描述區(qū)C）動(dòng)態(tài)分段區(qū)d）交易允許多個(gè)客戶端應(yīng)用程序共享一個(gè)單一的對(duì)象，服務(wù)器應(yīng)用程序執(zhí)行以下操作：（1）調(diào)用的SharedOb