外文翻译安卓系统的基本描述Word格式.docx
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外文翻译安卓系统的基本描述Word格式.docx
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BytheOpenMobileAlliance(openHandsetAllianceledbyGoogle)developedtheandroidsystemisawidelyoptimisticaboutanopensourcephonesystem,thesystemprovidesabasicoperatingsystem,amiddlewareapplicationlayer,ajavadevelopmenttoolsandasystemApplicationcollector(collectionofsystemapplications).TheandroidtheSDKsince2007onthereleaseofthefirstandroidphoneinOctober2008beforethebirth.Googleopenedsincethenonhisowntime,Taiwan'
sHTC,themanufactureroftheT-MobileG1estimateG1shipmentshavemorethanonemillionattheendof2008.AccordingtoindustryinsidersexpecttheG1mobilephonesalesin2009continue.Manyothermobilephonesuppliersinthenearfutureplanstosupportthissystem.
Aroundanandroidandahugedevelopercommunityhasbeenestablished,whilealotofnewproductsandapplicationsontheandroid.Android'
smainsellingpointisthatitenablesdeveloperstoseamlesslyexpandonlineservicestomobilephones.ThisisthemostobviousexampleisGoogle'
stightlyintegratedwithGmail,CalendarandContactsWebapplicationsthroughthesystem.Usersonlyneedtoprovideanandroidusernameandpassword,thephoneautomaticallysyncwithGoogleservices.Theothervendorsarequicklyadapttheirexistinginstantmessaging,socialnetworkingandgamingservices.Androidandmanycompaniesfindnewwaystointegratetheirexistingbusinesstotheandroid.
Traditionaldesktopandserveroperatingsystemhasbeenworkingfortheintegrationofsecurityfeatures.Theseindividualsandbusinessapplicationsonasingleplatformisverygood,howeverabusinessphoneplatformlikeandroidisnotveryuseful.Itgivesthehopeofmanyresearchers.Androidisnotparkedinthebodyforotherplatformapplicationsupport:
theimplementationoftheapplicationdependsonatop-levelJAVAmiddleware,themiddlewarerunningontheembeddedLinuxkernel.Therefore,developersshoulddeploytheirapplicationstotheAndroidmustuseacustomuserinterfaceenvironment.
Inaddition,theandroidsystemapplicationslimittheapplicationtocalleachotherAPIcollaboration,andtheothertoauthenticatetheuserapplication.Althoughtheseapplicationshavecertainsafetyfeatures,someofourexperienceddeveloperstocreateAndroidapplicationswhorevealedthatthedesignofsecurityapplicationsisnotalwaysstraightforward.Androidusesasimplepermissionlabeldistributionmodetorestrictaccesstoresources,butthereasonsforthenecessityandconvenienceofotherapplications,thedesignershaveincreasedtheconfusiononthissystem.ThispaperattemptstoexplainthecomplexityoftheAndroidsecurity,andpayattentiontosomeofthepossibledevelopmentdefectsandapplicationsecurity.Wetrytodrawsomelessonslearned,andhopethatthesafetyofthefuture.
Androidapplicationframeworkfordevelopersisamandatoryframework.Itdoesnothaveamain()functionfunctionorasingleentrypointfortheimplementationofthecontrary,thedevelopermustinthedesignofapplicationcomponents.WedevelopedapplicationstohelptheAPIoftheandroidsdk
TheAndroidsystemdefinesfourkindsofcomponenttype.
Activitycomponentthatdefinestheapplicationuserinterface.Usually,theapplicationdeveloperdefineseachactivityscreen.Activitycanstart,itmaypassandreturnvalues.CanbehandledatatimeonlyakeyboardsystemActivity,allotherActivitywillbesuspendedatthistime.
Servicecomponentsperformbackgroundprocessing.Theneedforsomeoperationswhenanactivity,afterthedisappearanceoftheuserinterface(suchasdownloadingafileorplayingmusic),itusuallytakesuchactionspeciallydesignedservices.Developerscanalsouseaspecialdaemonatsystemstartup,theserviceisusuallydefinedaremoteprocedurecall(RPC),andothersystemcomponentscanbeusedtosendtheinterfacecommandandretrievedata,aswellastoregisteracallbackfunction.
ContentProvidercomponentstorageandsharedatawithrelationaldatabaseinterfaces.EachContentsupplierhasanassociated"
rights"
todescribeitscontentscontains.OthercomponentswhenusedasahandletoexecuteSQLqueries(egSELECT,INSERT,orDELETEcontent.Contentsuppliersaretypicallystoredthevaluesonthedatabaserecords,dataretrievalisaspecialcase,thefileisalsosharedbythecontentproviderinterface.
Thecomponentsofthebroadcastreceiverastosendamessagefromthemailboxtotheapplication.Typically,thebroadcastmessage,theapplicationcodeimplicitdestination.Therefore,theradioreceiversubscribetothesedestinationsreceivemessagessenttoit.Theapplicationcodecanalsobesolvedexplicitlybroadcastreceivers,includingthenamespaceallocation.
ThemainmechanismoftheinteractionofthecomponentsoftheComponentInteraction,isanintent,whichisasimplemessageobject,whichcontainsadestinationaddressanddatacomponents.TheAndroidAPIdefineshisapproachintointent,andusethatinformationtoinitiateanactivitysuchasstartanactivity(startActivity(Anintent))startservices(thestartService(Anintent))andradio(sendBroadcast(Anintent)).Androidframeworktoinformthecallstothesemethodsbegantoperforminthetargetapplicationcode.Thisprocess,theinternalcomponentsofcommunicationiscalledanaction.Simplyput,theIntentobjectdefinedinthe"
Intenttoimplementthe"
action"
.OneofthemostpowerfulfeaturesoftheAndroidisallowedavarietyofintentaddressingmechanism.Thedevelopercansolvethespaceofatargetcomponentusingitsapplications,theycanalsospecifyanimplicitname.Inthelattercase,thesystemdeterminesthebestcomponentsofanactionbyconsideringtheinstalledapplicationsanduserchoice.
Implicitnameiscalledtheactionstringbecauseofhisspecialtypeoftherequestedaction.Suchasaviewactionstring,inanintentdatafieldpointstoanimagefile,thesystemwilldirectlyreferringtothepreferredimageviewer.
Developerscanalsousetheactionstringalargenumberofradiotosendandreceive.Receiveratthereceivingend,thedevelopersuseanintentfiltertocustomizethespecialactionstring.AndroidDepartment,includingtheadditionalgoaloftheresolutionrules,butanoptionalstringtypeofdatamanipulationisthemostcommon.
AndroidapplicationsarewrittenintheJavaprogramminglanguage.ThecompiledJavacode—alongwithanydataandresourcefilesrequiredbytheapplication—isbundledbytheapttoolintoanAndroidpackage,anarchivefilemarkedbyan.apksuffix.Thisfileisthevehiclefordistributingtheapplicationandinstallingitonmobiledevices;
it'
sthefileusersdownloadtotheirdevices.Allthecodeinasingle.apkfileisconsideredtobeoneapplication.
Inmanyways,eachAndroidapplicationlivesinitsownworld:
(1)Bydefault,everyapplicationrunsinitsownLinuxprocess.Androidstartstheprocesswhenanyoftheapplication'
scodeneedstobeexecuted,andshutsdowntheprocesswhenit'
snolongerneededandsystemresourcesarerequiredbyotherapplications.
(2)Eachprocesshasitsownvirtualmachine(VM),soapplicationcoderunsinisolationfromthecodeofallotherapplications.
(3)Bydefault,eachapplicationisassignedauniqueLinuxuserID.Permissionsaresetsothattheapplication'
sfilesarevisibleonlytothatuserandonlytotheapplicationitself—altoughtherearewaystoexportthemtootherapplicationsaswell.
It'
spossibletoarrangefortwoapplicationstosharethesameuserID,inwhilecasetheywillbeabletoseeeachother'
sfiles.Toconservesystemresources,applicationswiththesameIDcanalsoarrangetoruninthesameLinuxprocess,sharingthesameVM.
ApplicationComponents
AcentralfeatureofAndroidisthatoneapplicationcanmakeuseofelementsofotherapplication(providedthoseapplicationpermitit).Forexample,ifyourapplicationneedstodisplayascrollinglistofimagesandanotherapplicationhasdevelopedasuitablescrollerandmadeitavailabletoothers,youcancalluponthatscrollertodothework,ratherthandevelopyourown.Yourapplicationdoesn'
tincorporatethecodeoftheotherapplicationorlinktoit.Rather,itsimplystartsupthatpieceoftheotherapplicationwhentheneedarises.
Forthistowork,thesystemmustbeabletostartanapplicationprocesswhenanypartofitisneeded,andinstantiatetheJavaobjectsforthatpart.Therefore,unlikeapplicationsonmostothersystems,Androidapplicationsdon'
thaveasingleentrypointforeverythingintheapplication(nomain()function,forexample).Rather,theyhaveessentialcomponentsthatthesystemcaninstantiateandrunasneeded.Therearefourtypesofcomponents:
Activities
Anactivitypresentsavisualuserinterfaceforonefocusedendeavortheusercanundertake.Forexample,anactivitymightpresentalistofmenuitemsuserscanchoosefromoritmightdisplayphotographsalongwiththeircaptions.Atextmessagingapplicationmighthaveoneactivitythatshowsalistofcontactstosendmessagesto,asecondactivitytowritethemessagetothechosencontact,andotheractivitiestoreviewold
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