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龘龘龘:
TrueBrian 写道有个问题,Sample 1中,为了控制 ...
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龘龘龘:
楼主总结的不错。
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有个问题,Sample 1中,为了控制线程的启动时机,博主实际 ...
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本文部分内容节选自Enterprise JavaBeans 3.0 by Bill Burke & Richard Monson-Haefel
4 Persistence
EJB支持声明性事务,事务传播行为可以由TransactionAttribute annotation或者XML配置文件指定。事务属性有下列可选值:NotSupported、Supports、Required、RequiresNew、Mandatory和Never(Srping多支持一个NESTED)。默认的事务属性是Required。
伴随着事务的传播,persistence context也有特定的传播规则:
- 如果一个EJB调用了具有不同事务范围的另一个EJB,那么persistence context不会被传播。
- 如果在事务范围之外调用transaction scoped entity manager,会创建一个与调用时间等长的persistence context。
- 如果在事务范围内调用transaction scoped entity manager,并且当前没有persistence context与事务关联,那么会创建一个persistence context,当事务被提交或者回滚后,persistence context也就自动结束,被EntityManager管理的所有entity都变成detached状态。
- 如果在事务范围内调用extended entity manager,那么不论是否在事务内,entity manager在其整个生命周期内维护同一个persistence context。
- Stateful session bean是唯一允许借助@PersistenceContext注入extended persistence context的EJB组件。当stateful session bean被移除时,extended persistence context也会被关闭。
- 如果使用transaction scoped persistence context的EJB调用了使用extended persistence context的stateful session bean,那么会导致异常。
- 如果使用extended persistence context的stateful session bean调用了另一个注入transaction scoped persistence context的EJB,那么extended persistence context会被传播。
- 如果使用extended persistence context的stateful session bean调用了另一个注入extended persistence context的stateful session bean,那么extended persistence context会被传播。
- Persistence context只是在注入本地接口时有效,如果被注入的是远程接口,则嵌套方和被嵌套方将不会共享persistence context。
以下是个简单的例子:
import javax.ejb.Local; @Local public interface StatelessLocal { void doStatelessLocal(Movie m); }
import javax.ejb.Remote; @Remote public interface StatelessRemote { void doStatelessRemote(Movie m); }
import javax.ejb.Stateless; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import javax.persistence.PersistenceContextType; import com.versus.ejb.injection.entitymanager.Movie; @Stateless public class StatelessImpl implements StatelessLocal, StatelessRemote { // @PersistenceContext(unitName = "ejb", type = PersistenceContextType.TRANSACTION) private EntityManager entityManager; public void doStatelessLocal(Movie movie) { // System.out.println("in StatelessImpl.doStatelessLocal()"); @SuppressWarnings("unused") Movie m2 = entityManager.find(Movie.class, new Integer(2)); // System.out.println(entityManager.contains(movie)); } public void doStatelessRemote(Movie movie) { // System.out.println("in StatelessImpl.doStatelessRemote()"); @SuppressWarnings("unused") Movie m2 = entityManager.find(Movie.class, new Integer(2)); // System.out.println(entityManager.contains(movie)); } }
import javax.ejb.Local; @Local public interface Stateful1Local { void doStatefulLocal(); }
import javax.ejb.Remote; @Remote public interface Stateful1Remote { void doStatefulRemote(); }
import javax.ejb.EJB; import javax.ejb.Stateful; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import javax.persistence.PersistenceContextType; @Stateful public class Stateful1Impl implements Stateful1Local, Stateful1Remote { // @PersistenceContext(unitName = "ejb", type = PersistenceContextType.EXTENDED) private EntityManager entityManager; // @EJB private StatelessLocal statelessLocal; @EJB private StatelessRemote statelessRemote; @EJB private Stateful2Local stateful2Local; @EJB private Stateful2Remote stateful2Remote; public void doStatefulLocal() { // System.out.println("in Stateful1Impl.doStatefulLocal()"); Movie m1 = entityManager.find(Movie.class, new Integer(1)); System.out.println(entityManager.contains(m1)); // statelessLocal.doStatelessLocal(m1); statelessRemote.doStatelessRemote(m1); // stateful2Local.doStatefulLocal(m1); stateful2Remote.doStatefulRemote(m1); } public void doStatefulRemote() { // System.out.println("in Stateful1Impl.doStatefulRemote()"); Movie m1 = entityManager.find(Movie.class, new Integer(1)); System.out.println(entityManager.contains(m1)); // statelessLocal.doStatelessLocal(m1); statelessRemote.doStatelessRemote(m1); // stateful2Local.doStatefulLocal(m1); stateful2Remote.doStatefulRemote(m1); } }
import javax.ejb.Local; @Local public interface Stateful2Local { void doStatefulLocal(Movie m); }
import javax.ejb.Remote; @Remote public interface Stateful2Remote { void doStatefulRemote(Movie m); }
import javax.ejb.Stateful; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import javax.persistence.PersistenceContextType; @Stateful public class Stateful2Impl implements Stateful2Local, Stateful2Remote { // @PersistenceContext(unitName = "ejb", type = PersistenceContextType.EXTENDED) private EntityManager entityManager; public void doStatefulLocal(Movie movie) { // System.out.println("in Stateful2Impl.doStatefulLocal()"); @SuppressWarnings("unused") Movie m3 = entityManager.find(Movie.class, new Integer(3)); // System.out.println(entityManager.contains(movie)); } public void doStatefulRemote(Movie movie) { // System.out.println("in Stateful2Impl.doStatefulRemote()"); @SuppressWarnings("unused") Movie m3 = entityManager.find(Movie.class, new Integer(3)); // System.out.println(entityManager.contains(movie)); } }
import java.util.Properties; import javax.naming.Context; import javax.naming.InitialContext; import javax.rmi.PortableRemoteObject; public class PersistenceTest { public static void main(String args[]) throws Exception { // Properties properties = new Properties(); properties.setProperty(Context.INITIAL_CONTEXT_FACTORY, "org.apache.openejb.client.LocalInitialContextFactory"); InitialContext ctx = new InitialContext(properties); // if(true) { Object ref1 = ctx.lookup("Stateful1ImplLocal"); Stateful1Local simpleStatefulLocal = (Stateful1Local)PortableRemoteObject.narrow(ref1, Stateful1Local.class); simpleStatefulLocal.doStatefulLocal(); Object ref2 = ctx.lookup("Stateful1ImplRemote"); Stateful1Remote simpleStatefulRemote = (Stateful1Remote)PortableRemoteObject.narrow(ref2, Stateful1Remote.class); simpleStatefulRemote.doStatefulRemote(); } } }
以上代码的输出是:
in Stateful1Impl.doStatefulLocal()
true
in StatelessImpl.doStatelessLocal()
true
in StatelessImpl.doStatelessRemote()
false
in Stateful2Impl.doStatefulLocal()
true
in Stateful2Impl.doStatefulRemote()
false
in Stateful1Impl.doStatefulRemote()
true
in StatelessImpl.doStatelessLocal()
true
in StatelessImpl.doStatelessRemote()
false
in Stateful2Impl.doStatefulLocal()
true
in Stateful2Impl.doStatefulRemote()
false
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