Question

In my application based on EJB3.0 and JBoss5 I need to implement functionality which allows multiple instructions to be processed simultaneously. E.g. there is a stateful listening EJB, which in case of receiving data (asynchronously) triggers pooled stateless beans to do computations. Running execution in one SLSB do not stops starting execution in another SLSB (in case of receiving request by SFSB before first SLSB finish its work). It’s all similar to Spring ThreadPoolTaskExecutor – task is passed into the queue and when there is a thread available to handle it, it gets it from the queue (everything is done parallel).

Unfortunately I cannot use Spring or other version of EJB spec (but I can use some JBoss-specific features). How can I implement such a thing? I thought about using MDB’s which acts as a task executors, but I am not very sure if it would be done simultaneously (that’s my first question ;)) and if it’s a right way of use JMS (not for “messaging” strictly).

Thanks in advance for all hints.

Piotr

Answer 1

Use org.jboss.ejb3.common.proxy.plugins.async.AsyncUtils. This executes code on any SLSB (or even other beans that have an interface) asynchronous.

An example:

@Stateless
public class SomeBean implements SomeBeanLocal {

    public Future<Order> getByUserIDAsync(Long userID) {
        SomeBeanLocal asyncSomeBean = AsyncUtils.mixinAsync(this);
        asyncSomeBean.getByUserID(userID);
        return (Future<Order>) AsyncUtils.getFutureResult(asyncSomeBean);
    }

    // normal non-async methods or other async methods here ...
}

This will dispatch the call to the managed thread pool that every EJB container has and return immediately. The code will then run in the background.

JMS and Message driven beans have indeed been used for this in the past, but it’s not the best tool for the JOB. You run into a bunch of transactional problems like messages not being send until the transaction commits etc. It’s also harder to return a value. EJB3 timers were also used for this, as they too execute code asynchronously.

I know you mentioned you can’t switch to another EJB version at the moment, but I would like to mention anyway that in EJB 3.1 one can use the @Asynchronous annotation. That really is the best way of tackling this problem.