Service5.java

@Stateless
public class Service5 {

    @Resource ManagedExecutorService mes;
    @Resource EJBContext ctx;
    @PersistenceContext(name="asdf") EntityManager em;
	
    @Asynchronous
    public void foo(CompletableFuture<String> cf, final PrintWriter pw) {

        //pw.write("<br>inside the service we can rollback, i.e. we have access to the transaction");
        //ctx.setRollbackOnly();

        //in EJB we can use EM
        KeyValuePair kvp = new KeyValuePair("asdf");
        em.persist(kvp);

        Future<String> f = mes.submit(new Callable<String>() {
            @Override
            public String call() throws Exception {
                try{
                    ctx.setRollbackOnly();
                    pw.write("<br/>inside executor service, we can rollback the transaction");
                }catch(Exception e){
                    pw.write("<br/>inside executor service, we CANNOT rollback the transaction: " + e.getMessage());
                }

                try{
                    //in task inside executor service we CANNOT use EM
                    KeyValuePair kvp = new KeyValuePair("asdf");
                    em.persist(kvp);
                    pw.write("...inside executor service, we can use the EM");
                }catch(TransactionRequiredException e){
                    pw.write("...inside executor service, we CANNOT use the EM: " + e.getMessage());
                }
...