7, EJB
(1) Spring and EJB
l Spring is a lightweight container, which can be used to replace EJB in many occasions.
l Spring makes access and implementation EJB easier
(2) EJB Access
l Using EJB usually:
Ø Service Locator: Care JNDI, initialize Context, EJB Home Find
Ø Business representative: Reduce coupling, hidden implementation details
l Use spring without these design patterns
(3) Access local SLSB
l Use local stateless session beans
Class = "... ejb.access.localStatelessSessionProxyFactoryBean"> Create a proxy with the service locator to access the EJB (Business representative) l You can exchange beans's implementation without changing customer code: customer program uses business interface instead of EJB specific interface (4) Accessing remote SLSB l Using remote stateless session bean Class = "... SimpleRemotestatelessSession ProxyFactoryBean"> (5) EJB implementation l AbstractEnterpriseBean Ø Loading BeanFactory: EJB Environment Variable EJB / BeanFactoryPath Specifies the location of the XML BeanFactory file in the classpath; the default BeanFactory is XMLApplicationContext l Application is just using EJB as the front end Ø Business logic is postponed to BeanFactory's bean (6) Implement SLSB l State SESSION bean l extension AbstractStateLessSessionBean Ø Save session context Ø Empty implementation EJBREMOVEØ EJBCREATE () method Ø Throw it in ejbactivate () and ejbpassivate () L subclasses must implement onejbcreate () l example: Class myslsb extends abstractStateLessSessionBean { protected void onejbcreate () throws createException { ... } Public void businessmethod () { Beanfactory bf = getBeanFactory (); MybusinessBean MBB = bf.getBean ("MybusinessBean"); ... } } (7) Implement SFSB l Keep status session bean l extended AbstractStateFulsessionBean Ø Save session context Ø Empty implementation EJBREMOVE Ø ejbcreate () method L subclasses must implement ejbcreate (), ejbactivate () and ejbpassivate () l example: Class mysfsb extends abstractStatefulsessionBean { Public void ejbcreate () throws createException { Loadbeanfactory (); ... } Public void ejbactivate () { ... } Public void ejbpassivate () { ... } Public void businessmethod () { Beanfactory bf = getBeanFactory (); MybusinessBean MBB = bf.getBean ("MybusinessBean"); ... } } (8) Implement MDB l example: Class mymdb extends abstractjmsmessagedrivenbean { protected void onejbcreate () throws createException { ... } Public void onMessage (Message message) { Beanfactory bf = getBeanFactory (); MybusinessBean MBB = bf.getBean ("MybusinessBean"); ... } }
