HibernateData Access with the Spring Framework文档格式.docx

HibernateData Access with the Spring Framework文档格式.docx

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sHibernateTemplateoffersasimplewaytoimplementHibernate-basedDAOswithoutcaringabouthandlingSessioninstancesorparticipatingintransactions.Noneedfortry-catchblocks,noneedfortransactionchecks.AsimpleHibernateaccessmethodcanbeaone-liner!

CombiningheterogeneousDAOsworksseamlessly,bothintermsofDAOinterfacesandparticipatingintransactions.Forexample,certainDAOscanbeimplementedonplainJDBC,preferablyviaSpring'

sJdbcTemplatetoavoidmanualexceptionhandling.

YoucanusealotofSpring'

sfeaturesrespectivelyclassesinalibrarystyle,aseverythingisdesignedasasetofreusableJavaBeans.Don'

tbediscouragedbythefactthatSpringcanserveasfullapplicationframeworktoo!

Theapplicationcontextconceptisanadditionalbenefit,notarequirementforusingotherSpringfeatures.Inanycase,you'

reinvitedtoreviewandleveragetheSpringapproach,nomattertowhatextent,beforedecidingtotaketheeffortandriskofbuildingsuchinfrastructurein-house.

1.Introduction:

ResourceManagement

Typicalbusinessapplicationsareoftenclutteredwithrepetitiveresourcemanagementcode.Manyprojectstrytoinventownsolutionsforthisissue,sometimessacrificingproperhandlingoffailuresforprogrammingconvenience.Springadvocatesstrikinglysimplesolutionsforproperresourcehandling:

Inversionofcontrolviatemplating,i.e.infrastructureclasseswithcallbackinterfaces,orapplyingAOPinterceptors.Theinfrastructurecaresforproperresourcehandling,andforappropriateconversionofspecificAPIexceptionstoanuncheckedinfrastructureexceptionhierarchy.

SpringintroducesaDAOexceptionhierarchy,applicabletoanydataaccessstrategy.FordirectJDBC,theJdbcTemplateclasscaresforconnectionhandling,andforproperconversionofSQLExceptiontotheDataAccessExceptionhierarchy,includingtranslationofdatabase-specificSQLerrorcodestomeaningfulexceptionclasses.ItsupportsbothJTAandJDBCtransactions,viarespectiveSpringtransactionmanagers.SpringalsooffersHibernateandJDOsupport,consistingofaHibernateTemplate/JdoTemplateanalogoustoJdbcTemplate,aHibernateInterceptor/JdoInterceptor,andaHibernate/JDOtransactionmanager.

Themajorgoalistoallowforclearapplicationlayering,withanydataaccessandtransactiontechnology,andforloosecouplingofapplicationobjects.Nomorebusinessobjectdependenciesonthedataaccessortransactionstrategy,nomorehard-codedresourcelookups,nomorehard-to-replacesingletons,nomorecustomserviceregistries.Onesimpleandconsistentapproachtowiringupapplicationobjects,keepingthemasreusableandfreefromcontainerdependenciesaspossible.

AlltheindividualdataaccessfeaturesareusableontheirownbutintegratenicelywithSpring'

sapplicationcontextconcept,providingXML-basedconfigurationandcross-referencingofplainJavaBeaninstancesthatdon'

tneedtobeSpring-aware.InatypicalSpringapp,manyimportantobjectsareJavaBeans:

dataaccesstemplates,dataaccessobjects（thatusethetemplates）,transactionmanagers,businessobjects（thatusethedataaccessobjectsandtransactionmanagers）,webviewresolvers,webcontrollers（thatusethebusinessobjects）,etc.

2.ResourceDefinitionsinanApplicationContext

Toavoidtyingapplicationobjectstohard-codedresourcelookups,SpringallowstodefineresourceslikeaJDBCDataSourceoraHibernateSessionFactoryasbeansinanapplicationcontext.Applicationobjectsthatneedtoaccessresourcesjustreceivereferencestosuchpre-definedinstancesviabeanreferences（theDAOdefinitioninthenextsectionillustratesthis）.ThefollowingexcerptfromanXMLapplicationcontextdefinitionshowshowtosetupaJDBCDataSourceandaHibernateSessionFactoryontopofit:

<

beanid="

myDataSource"

class="

org.springframework.jndi.JndiObjectFactoryBean"

>

<

propertyname="

jndiName"

value>

jdbc/myds<

/value>

/property>

/bean>

mySessionFactory"

org.springframework.orm.hibernate.LocalSessionFactoryBean"

mappingResources"

list>

product.hbm.xml<

/list>

hibernateProperties"

props>

propkey="

hibernate.dialect"

net.sf.hibernate.dialect.MySQLDialect<

/prop>

/props>

dataSource"

refbean="

/>

...

NotethatswitchingfromaJNDI-locatedDataSourcetoalocallydefinedonelikeaJakartaCommonsDBCPBasicDataSourceisjustamatterofconfiguration:

mons.dbcp.BasicDataSource"

destroy-method="

close"

driverClassName"

org.hsqldb.jdbcDriver<

url"

jdbc:

hsqldb:

hsql:

//localhost:

9001<

username"

sa<

password"

YoucanalsouseaJNDI-locatedSessionFactory,butthat'

stypicallynotnecessaryoutsideanEJBcontext（seethe"

containerresourcesvslocalresources"

sectionforadiscussion）.

3.InversionofControl:

TemplateandCallback

Thebasicprogrammingmodelfortemplatinglooksasfollows,formethodsthatcanbepartofanycustomdataaccessobjectorbusinessobject.Therearenorestrictionsontheimplementationofthesurroundingobjectatall,itjustneedstoprovideaHibernateSessionFactory.Itcangetthelatterfromanywhere,butpreferablyasbeanreferencefromaSpringapplicationcontext-viaasimplesetSessionFactorybeanpropertysetter.ThefollowingsnippetsshowaDAOdefinitioninaSpringapplicationcontext,referencingtheabovedefinedSessionFactory,andanexampleforaDAOmethodimplementation.

myProductDao"

product.ProductDaoImpl"

sessionFactory"

publicclassProductDaoImplimplementsProductDao{

privateSessionFactorysessionFactory;

publicvoidsetSessionFactory（SessionFactorysessionFactory）{

this.sessionFactory=sessionFactory;

}

publicListloadProductsByCategory（finalStringcategory）{

HibernateTemplatehibernateTemplate=newHibernateTemplate（this.sessionFactory）;

return（List）hibernateTemplate.execute（

newHibernateCallback（）{

publicObjectdoInHibernate（Sessionsession）throwsHibernateException{

Listresult=session.find（"

fromtest.Productproductwhereproduct.category=?

"

category,Hibernate.STRING）;

//dosomefurtherstuffwiththeresultlist

returnresult;

}）;

}

AcallbackimplementationcaneffectivelybeusedforanyHibernatedataaccess.HibernateTemplatewillcareforproperSessionopeningandclosinginanycase,andforautomaticallyparticipatingintransactions.Thetemplateinstancesarethread-safeandreusable,theycanthusbekeptasinstancevariablesofthesurroundingclass.

Forsimplesinglestepactionslikeasinglefind,load,saveOrUpdate,ordeletecall,HibernateTemplateoffersalternativeconveniencemethodsthatcanreplacesuchonelinecallbackimplementations.Furthermore,SpringprovidesaconvenientHibernateDaoSupportbaseclassthatprovidesasetSessionFactorymethodforreceivingaSessionFactory,andgetSessionFactoryandgetHibernateTemplateforusebysubclasses.Incombination,thisallowsforverysimpleDAOimplementationsfortypicalrequirements:

publicclassProductDaoImplextendsHibernateDaoSupportimplementsProductDao{

publicListloadProductsByCategory（Stringcategory）{

returngetHibernateTemplate（）.find（"

category）;

4.ApplyinganAOPInterceptorInsteadofaTemplate

AnalternativetousingaHibernateTemplateisSpring'

sAOPHibernateInterceptor,replacingthecallbackimplementationwithstraightHibernatecodewithinadelegatingtry/catchblock,andarespectiveinterceptorconfigurationintheapplicationcontext.ThefollowingsnippetsshowrespectiveDAO,interceptor,andproxydefinitionsinaSpringapplicationcontext,andanexampleforaDAOmethodimplementation.

myHibernateInterceptor"

org.springframework.orm.hibernate.HibernateInterceptor"

myProductDaoTarget"

se