chap10-middleware_and_app .pdf

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1、CHAPTER10MiddlewareandApplicationSoftwareInThisChapterÑDefiningmiddlewareÑDefiningapplicationsoftwareÑIntroducingreal-worldnetworkingandJavaexamplesofmiddlewareÑIntroducingreal-worldnetworkingandJavaexamplesusedinapplicationsoftwareThelinebetweenmiddlewareandapplication

2、softwareisblurred,whichiswhythischapterintroducesbothtogether.Middlewareissoftwarethathasbeenabstractedoutoftheapplica-tionlayerforavarietyofreasons.Onereasonisthatitmayalreadybeincludedaspartoftheoff-the-shelfOSpackage.Otherreasonstoremoveitfromtheapplicationlayerare:toa

3、llowreusabilitywithotherapplications,todecreasedevelopmentcostsortimebypurchasingitoff-the-shelf-throughathirdpartyvendor,ortosimplifyapplicationcode.Theremainingsec-tionsofthischapterdefinewhatmiddlewareandapplicationsoftwareisorisn’t,andprovidereal-worldpseudocodeexample

4、sofmiddlewareandapplicationsoftware.10.1WhatIsMiddleware?Inthemostgeneralterms,middlewaresoftwareisanysystemsoftwarethatisnottheOSkernel,devicedrivers,orapplicationsoftware.NotethatsomeOSesmayintegratemiddle-wareintotheOSexecutable(seeChapter9).Inshort,inanembeddedsystemm

5、iddlewareissystemsoftwarethattypicallysitsoneitherthedevicedriversorontopoftheOS,andcansometimesbeincorporatedwithintheOSitself.ApplicationLayerApplicationLayerApplicationLayerSystemSoftwareLayerSystemSoftwareLayerSystemSoftwareLayerMiddlewareOperatingSystemOperatingSyste

6、mMiddlewareMiddlewareDeviceDriversDeviceDriversDeviceDriversardwareLayerHardwareLayerHardwareLayerHFigure10-1:MiddlewarewithintheEmbeddedSystemsModel445Chapter10Middlewareisusuallythesoftwarethatmediatesbetweenapplicationsoftwareandthekernelordevicedriversoftware.Middlewa

7、reisalsosoftwarethatmediatesandservesdif-ferentapplicationsoftware.Specifically,middlewareisanabstractionlayergenerallyusedonembeddeddeviceswithtwoormoreapplicationsinordertoprovideflexibility,security,portability,connectivity,intercommunication,and/orinteroperabilitymechan

8、ismsbetweenapplications.Oneofthemainstrengthsinusingmiddlewareisthatitallowsforthereductionofthe