EJB Transactions in local method-calls

问题

In the following setup, does method B run in a (new) transaction?

An EJB, having two methods, method A and method B

public class MyEJB implements SessionBean
    public void methodA() {
       doImportantStuff();
       methodB();
       doMoreImportantStuff();
    }

    public void methodB() {
       doDatabaseThing();
    }
}

The EJB is container managed, with methodB in requires_new transaction, and method A in required transaction. thus:

<container-transaction id="MethodTransaction_1178709616940">
  <method id="MethodElement_1178709616955">
    <ejb-name>MyName</ejb-name>
    <method-name>*</method-name>
  <trans-attribute>Required</trans-attribute>
  </method>
  <method id="MethodElement_1178709616971">
    <ejb-name>MyName</ejb-name>
    <method-name>methodB</method-name>
  </method>
  <trans-attribute>RequiresNew</trans-attribute>
</container-transaction>

Now let another EJB call methodA with an EJB method call. methodA now runs in an transaction. Will the subsequent call to methodB from methodA run in the same transaction, or does it run in a new transaction? (mind, it's the actual code here. There is no explicit ejb-call to method B)

回答1:

Your call to methodB() is an ordinary call of a method, not intercepted by the EJB container; at run-time the EJB container will inject a proxy and not an instance of your class, this is the way it intercepts calls and setup the environment before calling your method. If you use this you're calling a method directly and not through the proxy. Hence both methods will use the same transaction, regardless to what is defined in ejb-jar.xml for calls through EJB interfaces.

回答2:

inject SessionContext, and ask it for your proxy instance:

@Stateless
public class UserFacade implements UserFacadeLocal {
@Resource
private SessionContext context;

@Override
@TransactionAttribute(TransactionAttributeType.REQUIRED)
private void create(User user) {
        System.out.println("Users Count: "+count()); //invocation#1
        System.out.println("Users Count Through Context: "+context.getBusinessObject(UserFacadeLocal.class).count()); //invocation#2
    }

@Override
@TransactionAttribute(TransactionAttributeType.NEVER)
    public int count() {
        return ((Long) q.getSingleResult()).intValue();
    }
}

in 'invocation#1' this is a Local call, not passing through proxy, it will return the count

in 'invocation#2' this is a call through the proxy, and hence you annotate it not to support transaction -which is now opened by create(user) method-, this invocation will throw a transaction exception:

javax.ejb.EJBException: EJB cannot be invoked in global transaction

回答3:

They will use the same transaction.

If I remember well, the transaction is started by the container "before" the method is invoked and commited after it "finish".

Since "a" calls "b", "b" would use the same transaction.

I guess the best thing you can do is test it to verify it! :)

来源：https://stackoverflow.com/questions/427452/ejb-transactions-in-local-method-calls

标签

java-ee

transactions

ejb