Jan 24 2011

@OneToOne reversemapping and lazy loading

Frank

Using JPA or especially Hibernate for mapping database tables to POJOs is quite comfortable. An essential feature here is lazy loading of constraints between objects. Unfortunately this didn’t work out of the box for reversed @OntToOne relations.
For example you have two classes:

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public class A {
   @OneToOne(fetch=FetchType.LAZY)
   private B foo;
}
 
public class B {
    @OneToOne(mappedBy = "foo", fetch = FetchType.LAZY)
    private A bar;
 
    public A getBar() {
        return bar;
    }
}

If you now load B from the database Hibernate needs to look if A also exists, because Hibernate needs to know if “bar” is null or not. In this case the parameter “fetch” has no effect. There are two known possible solutions to solve this problem:

  1. Implement the “bar” relation as @OneToMany with a collection and implement getBar as you needed. But if you need this relation in complex queries you could have problems to define the correct HQL.
  2. You use Bytecode instrumentation to realize a real lazy loading behaviour. In this case you have to add the following annotation to the property “bar”: @LazyToOne(LazyToOneOption.NO_PROXY)

no comments   |  tags: , , , , , | posted in Hibernate, Java

Nov 1 2009

Using TransactionAttribute in submethods on same EJB3-Beans

Frank

The EJB3 Standard provides some annotations to handle general approaches, like transactions (@TransactionAttribute) and security (@RolesAllowed, etc.). To use these methods, you only have to add them to the concerning method.

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@Stateless
@Local(SampleStateless.class)
public class SampleStatelessBean implements SampleStateless {
    @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
    public void sampleMethod() {
        // do some stuff
    }
}

Sometimes you have to call methods of other business objects to handle the business logic. For example you have a batch update separated into many small update steps. Here you want to split the main transaction into several small transactions and the main part should have no transaction, because it only handles the reading of external data (The example code is not complete and should only demonstrate the usage of the annotations.).

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@Stateless
@Local(SampleStateless.class)
public class SampleStatelessBean implements SampleStateless {
    @TransactionAttribute(TransactionAttributeType.NEVER)
    public void import() {
       //read some data
       while (haveData) {
           importData(subData);
       }
    }
 
    @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
    private void importData(List data) {
        // do some stuff
    }
}

This above code is unfortunately NOT CORRECT. The reason is that the @TransactionAttribute-annotations will only be honored, if you call the method via a business interface. So the first solutions is to inject the bean itself and call the submethod via the injected bean.

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@Stateless
@Local(SampleStateless.class)
public class SampleStatelessBean implements SampleStateless {
    @EJB
    private SampleStateless bp;
 
    @TransactionAttribute(TransactionAttributeType.NEVER)
    public void import() {
       //read some data
       while (haveData) {
           bp.importData(subData);
       }
    }
 
    @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
    public void importData(List data) {
        // do some stuff
    }
}

Another solution, which is quite faster on JBoss in my tests, is to use the SessionContext to get a reference to the current business object.

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@Stateless
@Local(SampleStateless.class)
public class SampleStatelessBean implements SampleStateless {
    private SampleStateless bp;
 
    @Resource
    private SessionContext ctx;
 
    @PostConstruct
    public void init() {
        bp = ctx.getBusinessObject(SampleStateless.class);
    }
 
    @TransactionAttribute(TransactionAttributeType.NEVER)
    public void import() {
       //read some data
       while (haveData) {
           bp.importData(subData);
       }
    }
 
    @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
    public void importData(List data) {
        // do some stuff
    }
}

no comments   |  tags: , , , , | posted in Java, JBoss

Okt 13 2009

Classloading problems with injected @EJB-Beans

Frank

Yesterday I wrote how to define Quartz-Jobs in JBoss AS. Generally such jobs try to use business logic, which is injected via @EJB. Currently in Version 5.1.0.GA this is not possible if you use the classloader-isolation. You will get the following (or similar) exception:

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Caused by: java.lang.RuntimeException: Can not find interface declared by Proxy in our CL + BaseClassLoader@92c904{vfsfile:...}
at org.jboss.ejb3.proxy.impl.objectfactory.ProxyObjectFactory.redefineProxyInTcl(ProxyObjectFactory.java:343)
at org.jboss.ejb3.proxy.impl.objectfactory.session.SessionProxyObjectFactory.createProxy(SessionProxyObjectFactory.java:134)
at org.jboss.ejb3.proxy.impl.objectfactory.session.stateless.StatelessSessionProxyObjectFactory.getProxy(StatelessSessionProxyObjectFactory.java:79)
at org.jboss.ejb3.proxy.impl.objectfactory.ProxyObjectFactory.getObjectInstance(ProxyObjectFactory.java:158)
at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:304)
at org.jnp.interfaces.NamingContext.getObjectInstance(NamingContext.java:1479)
at org.jnp.interfaces.NamingContext.getObjectInstanceWrapFailure(NamingContext.java:1496)
... 39 more

The reason for this ist that the Quartz-Service has another classloader as your application and the started job contains to the classloader of the Quartz-Service. There is also a bug posted. Maybe this will be possible in the near future.
One solution is to call a MBean from the job and this MBean injects the business logic via @EJB. The advantage of this solution is that you also can control and monitor the cronjob itselfs and can run the logic on demand via JMX-Console.
An example job would look like:

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@MessageDriven(messageListenerInterface = StatefulJob.class, activationConfig = { @ActivationConfigProperty(propertyName = "cronTrigger", propertyValue = "0 0 0 ? * MON-SAT") })
@ResourceAdapter("quartz-ra.rar")
@Depends(ImportDataManagement.ID)
public class DailyUpdateJob implements StatefulJob {
    private static final Logger log = Logger
            .getLogger(DailyUpdateJob.class);
 
    public void execute(JobExecutionContext context)
            throws JobExecutionException {
        try {
            MBeanServer server = MBeanServerLocator.locate();
            ImportDataManagement bp = (ImportDataManagement) MBeanProxyExt
                    .create(ImportDataManagement.class,
                            ImportDataManagement.ID, server);
            bp.importDaily();
        } catch (Exception e) {
            log.error("run", e);
        }
    }
}

Helpful links:

no comments   |  tags: , , , , , | posted in JBoss