Apache Jackrabbit 官网代码示例First Hops.docx

Apache Jackrabbit 官网代码示例First Hops.docx

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ApacheJackrabbit官网代码示例FirstHops

FirstHops

WelcometoyourfirsthopsintotheworldofJackrabbit!

Thisintroductiongivesyouahands-onexperiencewithJackrabbitandtheJCRAPI.Onceyouhavefinishedhoppingthroughthisdocument,youshouldbeallsettocontinueonyourownwiththeofficialJCRspecificationandthedocumentationonthissite.

Hop0:

Gettingstarted

TheeasiestwaytogetstartedwithJackrabbitistodownloadtherunnableStandaloneServerjar.Inadditiontorunningit,youcanalsoputitinyourclasspathtoquicklyaccessalltheclassesandinterfacesyouneedbelow.Alternatively,ifyouusetheApacheMavenbuildsystem（whichwerecommend）,youcansetupyourfirsthopsprojectwiththefollowingdependencies.

--TheJCRAPI-->

javax.jcr

jcr

2.0

--Jackrabbitcontentrepository-->

org.apache.jackrabbit

jackrabbit-core

2.2.4

--UseLog4Jforlogging-->

org.slf4j

slf4j-log4j12

1.5.11

YouprobablyhaveanerrorinyourclasspathsettingsifyougetaClassNotFoundExceptionmessagewhentryingtocompileorruntheexamplesbelow.

Hop1:

LoggingintoJackrabbit

Solet’sgetstarted.Asawarm-upwe’llcreateaJackrabbitcontentrepositoryandstartaloginsessionforaccessingit.Thefullexampleapplicationthatdoesthisisshownbelow,withline-by-lineexplanationsfollowingshortlyafter.

importjavax.jcr.Repository;

importjavax.jcr.Session;

importorg.apache.jackrabbit.core.TransientRepository;

/**

*Firsthopexample.Logsintoacontentrepositoryandprintsa

*statusmessage.

*/

publicclassFirstHop{

/**

*Themainentrypointoftheexampleapplication.

*

*@paramargscommandlinearguments（ignored）

*@throwsExceptionifanerroroccurs

*/

publicstaticvoidmain（String[]args）throwsException{

Repositoryrepository=newTransientRepository（）;

Sessionsession=repository.login（）;

try{

Stringuser=session.getUserID（）;

Stringname=repository.getDescriptor（Repository.REP_NAME_DESC）;

System.out.println（

"Loggedinas"+user+"toa"+name+"repository."）;

}finally{

session.logout（）;

}

}

}

YoucanalsodownloadthesourcefileasFirstHop.java.Ifyouhaveyourclasspathsetup,youcancompiletheapplicationwithjavacFirstHop.javaandrunitwithjavaFirstHoptogetthefollowingoutput.

LoggedinasanonymoustoaJackrabbitrepository.

Inadditiontoproducingtheabovestatuslinetheapplicationcopiesadefaultrepositoryconfigurationfiletorepository.xmlandcreatesaninitialJackrabbitcontentrepositoryintherepositorysubdirectory.Youcanusethesystempropertiesorg.apache.jackrabbit.repository.confandorg.apache.jackrabbit.repository.hometosetalternativeconfigurationfileandrepositorydirectorylocations.

ReadonforadetailedbreakdownoftheFirstHopapplication:

importjavax.jcr.Repository;

importjavax.jcr.Session;

TheJCRAPIinterfacesarelocatedinthejavax.jcrpackagefoundinthejcr-1.0.jarlibrary.ThepromiseoftheJCRAPIisthatifyouonlyusetheseinterfacesinyourcontentapplication,itshouldremainmostlyindependentoftheunderlyingcontentrepositoryimplementation.

TheRepositoryinterfacerepresentsagivencontentrepositoryinstanceandtheSessioninterfacerepresentsasingleloginsessionforaccessingtherepository.Asessionisneededtoaccessanycontentwithinarepository.

NotethataSessioninstanceisnotguaranteedtobethread-safesoyoushouldstartmultiplesessionsifyouneedtoaccessrepositorycontentsimultaneouslyfromdifferentthreads.Thisisespeciallyimportantforthingslikewebapplications.

importorg.apache.jackrabbit.core.TransientRepository;

ThebestpracticefordeployingJackrabbitistouseJNDIorsomeotherconfigurationmechanisminacontainerenvironmenttokeeptheapplicationcodefreeofdirectJackrabbitdependencies,butsincewearecreatingasimplestandaloneapplicationwecantakeashortcutbyusingtheTransientRepositoryclassfromJackrabbitcore.

publicclassFirstHop

publicstaticvoidmain（String[]args）throwsException

TheFirstHopexampleisasimplestandaloneapplicationthatfitsnicelyinthemain（）methodandletstheJVMtakecareofthepossibleexceptions.MoresubstantialcontentapplicationscouldalsobewrittenaswebapplicationorEJBcomponentswithdifferentsetupanderrorhandlingpatterns.

Repositoryrepository=newTransientRepository（）;

TheTransientRepositoryclassimplementstheJCRRepositoryinterface,soyoucansimplyassignaTransientRepositoryinstancetoaRepositoryvariable.Thedefaultconstructorcontainsautilityfeaturethatwilltakecareoftheinitialconfigurationandrepositoryconstructionwhenthefirstsessionisstarted.Thusthereisnoneedformanualconfigurationfornowunlessyouwantdirectcontrolovertherepositorysetup.

TheTransientRepositoryimplementationwillautomaticallyinitializethecontentrepositorywhenthefirstsessionisstartedandshutitdownwhenthelastsessionisclosed.Thusthereisnoneedforexplicitrepositoryshutdownaslongasallsessionsareproperlyclosed.NotethataJackrabbitrepositorydirectorycontainsalockfilethatpreventsitfrombeingaccessedsimultaneouslybymultipleprocesses.Youwillseerepositorystartupexceptionscausedbythelockfileifyoufailtoproperlycloseallsessionsorotherwiseshutdowntherepositorybeforeleavingtheprocessthataccessesarepository.Normallyyoucanjustmanuallyremovethelockfileinsuchcasesbutsuchcasesalwayspresentachanceofrepositorycorruptionespeciallyifyouuseanon-transactionalpersistencemanager.

Sessionsession=repository.login（）;

ThedefaultRepository.login（）methodstartsarepositorysessionusingthedefaultworkspaceandnousercredentials.JackrabbittriestousetheJavaAuthenticationandAuthorizationService（JAAS）configurationinsuchcases,butdefaultstotheanonymoususerifaJAASSubjectisnotfound.

SinceweusetheTransientRepositoryclassastheRepositoryimplementation,thisstepwillalsocausetherepositorytobeinitialized.

try{...}finally{session.logout（）;}

Itisagoodpracticetoproperlyreleaseallacquiredresources,andtheJCRsessionsarenoexception.Thetry-finallyidiomisagoodwaytoensurethataresourcereallygetsreleased,asthereleasemethodgetscalledeveniftheinterveningcodethrowsanexceptionorotherwisejumpsoutsidethescope（forexampleusingareturn,break,orcontinuestatement）.

TheSession.logout（）methodinthefinallybranchclosesthesessionandsincethisistheonlysessionwehavestarted,theTransientRepositoryisautomaticallyshutdown.

Stringuser=session.getUserID（）;

TheusernameoridentifieroftheuserassociatedwithasessionisavailableusingtheSession.getUserID（）method.Jackrabbitreturns"anonymous"bydefault.

Stringname=repository.getDescriptor（Repository.REP_NAME_DESC）;

Eachcontentrepositoryimplementationpublishesanumberofstringdescriptorsthatdescribethevariousimplementationproperties,liketheimplementationlevelandthesupportedoptionalJCRfeatures.SeetheRepositoryinterfaceforalistofthestandardrepositorydescriptors.TheREP_NAME_DESCdescriptorcontainsthenameoftherepositoryimplementation,inthiscase"Jackrabbit".

Hop2:

Workingwithcontent

Themainfunctionofacontentrepositoryisallowapplicationstostoreandretrievecontent.ThecontentinaJCRcontentrepositoryconsistsofstructuredorunstructureddatamodeledasahierarchyofnodeswithpropertiesthatcontaintheactualdata.

Thefollowingexampleapplicationfirststoressomecontenttotheinitiallyemptycontentrepository,thenretrievesthestoredcontentandoutputsit,andfinallyremovesthestoredcontent.

importjavax.jcr.Repository;

importjavax.jcr.Session;

importjavax.jcr.SimpleCredentials;

importjavax.jcr.Node;

importorg.apache.jackrabbit.core.TransientRepository;

/**

*Secondhopexample.Stores,retrieves,andremovesexamplecontent.

*/

publicclassSecondHop{

/**

*Themainentrypointoftheexampleapplication.

*

*@paramargscommandlinearguments（ignored）

*@throwsExceptionifanerroroccurs

*/

publicstaticvoidmain（String[]args）throwsException{

Repositoryrepository=newTransientRepository（）;

Sessionsession=repository.login（

newSimpleCredentials（"username","password".toCharArray（）））;

try{

Noderoot=session.getRootNode（）;

//Storecontent

Nodehello=root.addNode（"hello"）;

Nodeworld=hello.addNode（"world"）;

world.setProperty（"message","Hello,World!

"）;

session.save（）;

//Retrievecontent

Nodenode=root.getNode（"hello/world"）;

System.out.println（node.getPath（））;

System.out.println（node.getProperty（"message"）.getString（））;

//Removecontent

root.getNode（"hello"）.remove（）;

session.save（）;

}finally{

session.logout（）;

}

}

}

Likeinthefirsthop,thisexamplesourceisalsoavailableasSecondHop.java.Youcanalsocompileandrunthisclassjustlikeyoudidinthefirsthopexample.Runningthisexampleshouldproducethefollowingoutput:

/hello/world

Hello,World!

ThebasicstructureofthisexampleapplicationisthesameasintheFirstHopexample,solet’sjustwalkthroughthedifferences:

importjavax.jcr.SimpleCredentials;

importjavax.jcr.