Java EE Future NullPointer

Question

I'm new to java.util.concurrent package and i came to a problem with Future object.

This is a conversationScoped bean.

@Inject SomeBean stateFull;

Boolean comp = false, comp1 = false;

public void doSomething(){        

    stateFull.runProcess();   

    try {

        comp = stateFull.getFuture().get();    
        System.out.println("Future "+syncEJB.getFuture().get());
        updateView();

        comp1 = stateFull.getFuture1().get();   
        System.out.println("Future "+syncEJB.getFuture().get());
        updateView();

    } catch (InterruptedException ex) {
        Logger.getLogger(SynchronizationMB.class.getName()).log(Level.SEVERE, null, ex);
    } catch (ExecutionException ex) {
        Logger.getLogger(SynchronizationMB.class.getName()).log(Level.SEVERE, null, ex);
    }


}

SomeBean looks like this.

@Stateful
public class SomeBean{    

    @Inject AnotherBean stateLess;

    private volatile Future<Boolean> future, future1;

    @Asynchronous
    public void runProcess(){
        future = stateLess.compute(); 
        future1 = stateLess.compute(); 

    }
    public Future<Boolean> getFuture() {
        return future;
    }
    public Future<Boolean> getFuture1() {
        return future1;
    }
}

And AnotherBean:

@Stateless
public class AnotherBean{

@Asynchronous
public Future<Boolean> compute() {
    boolean result;


    System.out.println("--------------");
    System.out.println("completed sync");
    System.out.println("--------------");

    result = true;

    return new AsyncResult<Boolean>(result);
}
}

And now to my problem. I call doSomething() method and i think that according to documentation of Future.get() it should call runProcess() and than wait at
comp = stateFull.getFuture().get();
until future in SomeBean is completed from AnotherBean, but it just keep throwing NullPointerException. Anyone knows why it can be be happening?

-------------------EDIT-----------------------

NullPointer has been corrected. Now i have another problem. Let's say that i set more Future objects in Somebean by calling more methods in runProcess(). And then i want to update my page everytime the Future object get a result to see the progress. How do i do that? Right now i use

private void updateView(){
    RequestContext ctx = RequestContext.getCurrentInstance();
    ctx.update("mainFrm:info");
}

under every Boolean in doSomething() method, but it doesnt do what i want. All booleans just appear all at once.

Why aren't you simply defining: public Future<Boolean> runProcess(){ return stateLess.compute(); }, what's the purpose of this extra variable? — Tomasz Nurkiewicz
– Tomasz Nurkiewicz, Commented Aug 17, 2012 at 11:38
because i will be calling more of similar methods in runProcess() right now theres only one for testing purpose, same with that boolean in conversationScoped bean, there will be more — Pája Jirásek
– Pája Jirásek, Commented Aug 17, 2012 at 11:44
first find which value is null, looking at the stack trace: is at stateFull.runProcess() or at stateFull.getFuture().get()? — Alexei Kaigorodov
– Alexei Kaigorodov, Commented Aug 17, 2012 at 11:49
it is selected in code where nullpointer occures, at stateFull.getFuture().get() — Pája Jirásek
– Pája Jirásek, Commented Aug 17, 2012 at 11:56

ice · Accepted Answer · 2012-08-17 11:47:34Z

3

NPE happens because starting new thread is a heavy operation, and when you call stateFull.getFuture().get(); new thread is not started yet(so feature is null).

Here the right way of using @Async with Future.

answered Aug 17, 2012 at 11:47

ice

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4 Comments

Pája Jirásek Over a year ago

nice idea but looks like not source of problem. I tryed to set Thread object like this thisThread = Thread.currentThread(); in SomeBean of this Asynchronous call and than check in while cycle till its alive in conversationScoped bean but nullPointer remains

ice Over a year ago

future filed must be at least volatile - because it updated and obtained in different threads.

Pája Jirásek Over a year ago

ok so now it stopped throwing NPE but IllegalStateException started. Object does not represent an acutal Future

Pája Jirásek Over a year ago

great thanks you very much. The last exception was cause by me using get() with timeout attribute :)

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