Java EE EJB作为可运行执行器

Question

Is this code copmliant to Java EE spec and can be used?

@Stateless
public class SomeBean {

    @Inject
    protected TransactedRunner txRunner;


    public void someFunc() {

        txRuner.run(new Runnable(){
            Connection c = ds.getConnection();
            //do jdbc stuff or jpa stuff
            //close everything etc.
        });
    }
}

@Stateless
public class TransactedRunner {

    @TransactionAttribute(REQUIRES_NEW)
    public void run(Runnable r) {
        r.run();
    }
}

In this case a new transaction should be started and every thing that will be done in runnable will be transacted. Is that right? Or there is some trick in which I should suffer from EE?

Answer 1

There is an annotation in JavaEE6 called @Asynchronous which is specifically for this purpose. Here is the official tutorial: http://docs.oracle.com/javaee/6/tutorial/doc/gkkqg.html

@Stateless
public class SomeBean {

    @Inject
    private SomeBean self;

    public void someFunc() {
        self.doSomething();
    }

    @TransactionAttribute(REQUIRES_NEW)
    @Asynchronous
    private void doSomething() {
        Connection c = ds.getConnection();
        //do jdbc stuff or jpa stuff
        //close everything etc.
    }
}

Also it's not allowed to create or manage Threads within a EJB Container. Check out: http://www.oracle.com/technetwork/java/restrictions-142267.html#threads

Why is thread creation and management disallowed?

The EJB specification assigns to the EJB container the responsibility for managing threads. Allowing enterprise bean instances to create and manage threads would interfere with the container's ability to control its components' lifecycle. Thread management is not a business function, it is an implementation detail, and is typically complicated and platform-specific. Letting the container manage threads relieves the enterprise bean developer of dealing with threading issues. Multithreaded applications are still possible, but control of multithreading is located in the container, not in the enterprise bean.

Answer 2

Method "run" will be executed in transaction, that's true. But it has nothing in common with threading or using executor. In your example, the calling thread will execute your "run" method. Runnable interface itself won't create a separate thread for you.

If you need this call to be executed by separate thread, you can use asynchronous calls, or, starting from EE7, a ManagedExecutorService is available:

http://docs.oracle.com/javaee/7/api/javax/enterprise/concurrent/ManagedExecutorService.html

Answer 3

This should work as intended. But be aware, that multiple calls of txRunner.run during one service call might lead to inconsistent data if anything happens between or during those calls, like connection-timeout, transaction-timeout, or the node dies or something. And the calling transaction (if there is any) might not see the changes done during the call until it itself has been committed.