服務器應用程序中英文對照外文翻譯文獻

服務器應用程序中英文對照外文翻譯文獻PAGEPAGE1服務器應用程序中英文對照外文翻譯文獻(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的用戶對象在開發(fā)分布式程序中的應用0引言面向對象的方法和工具軟件已經(jīng)在發(fā)展中國家提出并廣受歡迎。PowerBuilder用戶對象的模擬類是面向對象的概念，這是PowerBuilder的發(fā)展表現(xiàn)最柔韌的對象之一。開發(fā)人員可以使用PowerBuilder開發(fā)的主要對象功能，添加新的用戶定義的組件和提高代碼的重用。此外，我們可以開發(fā)C++來提高組件速度敏感的部位，并導入它們在PowerBuilder中的程序。有兩種PowerBuilder對象：其中之一是可視對象，它們可以用于應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的業(yè)務邏輯。用戶對象——其他PowerBuilder對象，包含一些屬性，如事件，實例變量，用戶對象等功能。一般來說，一個不可視對象代表了系統(tǒng)的分析類。我們不打算討論如何定義實例變量和編寫用戶對象的功能，您可以參考PowerBuilder的文件。通常我們使用的非可視化對象執(zhí)行PowerBuilder的分布式應用程序。分布式計算是一個使用的客戶機/服務器架構的網(wǎng)絡計算機系統(tǒng)的發(fā)展的自然產(chǎn)物。它可以讓你得到客戶機/服務器架構。分布式計算的概念是緊密相連的RPC（遠程過程調(diào)用）。RPC是技術，客戶端程序可以調(diào)用遠程進程（功能）計算機，并得到處理結果（函數(shù)的返回值）。PowerBuilder保護RPC的許多細節(jié)并可以很容易地開發(fā)服務器和客戶端應用程序。1在服務器上的應用，用戶對象一個遠程對象是一個自定義類（非可視）在位于遠程服務器上的應用程序中的用戶對象。每個遠程對象是一個自定義類用戶（非可視），已被提到，在用戶對象的遠程服務器上的應用程序的一部分，他們的客戶提供服務的對象?？梢哉{(diào)用遠程對象的跨進程，跨計算機邊界。也就是說，客戶端應用程序可以調(diào)用遠程對象與同一臺計算機上或在網(wǎng)絡的另一臺計算機上的單獨的可執(zhí)行文件。成功的分布式應用開發(fā)的關鍵是使用面向對象技術和精心選擇的遠程對象。PowerBuilder的分布式計算的支持是它的對象導向架構的一個合乎邏輯的延伸。出于這個原因，使用面向對象技術的一個PowerBuilder應用程序可以轉換為以最小的分布式應用程序難度。當您準備開始開發(fā)分布式應用程序，你需要到你的業(yè)務邏輯封裝在自定義類（非可視）用戶對象。定制類用戶對象提供任何分布式應用的基礎。一旦你創(chuàng)建了你的不可視對象，可以使客戶端應用程序所需的遠程訪問這些對象的調(diào)整。任何自定義類用戶對象可以作為一個服務器應用程序的遠程對象。然而，并不是所有的非可視化對象都是分布式處理的很好的候選人。由于網(wǎng)絡和服務器的性能，可以降低部署在遠程服務器上，如果太多的對象，你需要有選擇性的來決定進行遠程的對象。1.1遠程對象服務器應用程序的基本構件是它所包含的遠程對象。每個遠程對象是一個自定義類（非可視）用戶對象，可以由一個或多個客戶端應用程序調(diào)用的方法。一個典型的服務器應用程序包含了幾個業(yè)務邏輯封裝成可重用的組件不可視對象。因此，建立一個服務器應用程序的首要任務是寫出非可視化對象的方法。1.1.1實例變量實例存在于內(nèi)存中，并分配給其應有的關系和變量的值。1.1.2通過引用傳遞你可以傳遞參數(shù)參考組件的方法。然而，比在非分布式的應用程序，在分布式應用程序的行為是有點不同。當你通過引用傳遞，變量實際上是復制到服務器的方法執(zhí)行之前，然后復制回當該方法完成執(zhí)行。這種行為通常是透明的應用程序，但在某些情況下，它可以影響處理結果。例如，假設你定義increment_值的方法，稱為X和Y兩個參數(shù)，這兩者都是通過引用傳遞。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調(diào)用該方法：整型Z，Z=1遞增值（Z，Z）在非分布式的應用程序，完成后的z值的方法，將執(zhí)行3（因為本地調(diào)用傳遞一個指針到z，z是遞增的兩倍）。在分布式應用程序，z的值是2（因為遠程調(diào)用傳遞z的兩個副本，分別遞增）。1.1.3數(shù)據(jù)類型的返回值在服務器應用程序的非可視化對象的方法可以使用??下列數(shù)據(jù)類型：標準的數(shù)據(jù)，類型，結構，自定義類（非可視）用戶對象的參數(shù)。一個遠程對象的方法的返回值可以是任何類型的標準數(shù)據(jù)。返回值也可以是自定義類（非可視）用戶對象或結構，而不是一個結構數(shù)組。1.2共享對象為了讓您的工作充滿執(zhí)著，在分布式應用程序共享數(shù)據(jù)，PowerBuilder提供了對共享對象的支持。共享對象是用戶共享的對象，可以由多個客戶端連接離子。電力建設者在執(zhí)行時，為每個共享對象實例和共享對象創(chuàng)建的任何對象創(chuàng)建一個單獨的線程（會話）。因此，里面的共享對象進行的任何工作將運行在一個單獨的線程。你可以分享任何自定義類（非可視）用戶對象創(chuàng)建。此外，您可以共享許多內(nèi)置的，這是與PowerBuilder的，以及標準類用戶對象繼承這些內(nèi)置對象的非可視化對象。然而，PowerBuilder中不允許你分享以下類型的對象：A）數(shù)據(jù)存儲B）動態(tài)描述區(qū)C）動態(tài)分段區(qū)d）交易允許多個客戶端應用程序共享一個單一的對象，服務器應用程序執(zhí)行以下操作：（1）調(diào)用的SharedOb