Event firing/matching and parameterized types

[ljnelson]

(For background, I've read You think you know everything about CDI events… Think again! | Next Presso , so I'm at least mostly familiar with many edge cases in CDI events.)

I have an AbstractFoo<? extends T> as a payload that I want to fire.

T is defined as T extends MetaData.

For various unimportant reasons I have to fire my payload programmatically, so I do this:

final Event<Object> cdiEventMachinery = beanManager.getEvent();

assert cdiEventMachinery != null;

final TypeLiteral<AbstractFoo<? extends T>> eventTypeLiteral = new TypeLiteral<AbstractFoo<? extends T>>() {

    private static final long serialVersionUID = 1L;

  };

final Event<AbstractFoo<? extends T>> broadcaster = cdiEventMachinery.select(eventTypeLiteral, someQualifiers);

assert broadcaster != null;

Obviously here broadcaster is now set up to fire my payload.  My intention is that these events should be delivered to observers looking for AbstractFoo-or-its-subclasses instances parameterized by any type that extends MetaData.

Now, when I do broadcaster.fire(payload), I've noticed that observer methods like this one:

private final void onFoo(@ObservesAsync @MatchingQualifier final Foo<? extends MetaDataSubclass> event) {}

…do not get called.  (The ? extends MetaDataSubclass seems to be the culprit; if the observed parameter is simply, say, Object then obviously the method is notified.)

Specifically, assuming that:

• a MatchingQualifier literal is present in someQualifiers, and
• MetaDataSubclass is a class that extends MetaData, and
• Foo is a class that extends AbstractFoo

…why doesn't that observer method get called?

To be clear, I'm sure this isn't a bug but is something missing in my understanding.  I'd like to find out what I'm missing.

Best,

Laird

[ljnelson]

Here's a test case using more simple constructs:

  private final void collectionExtendsNumber(@Observes final Collection<? extends Number> payload) {

    System.out.println("*** collection extends Number");

  }

  private final void collectionExtendsInteger(@Observes final Collection<? extends Integer> payload) {

    System.out.println("*** collection extends Integer");

  }

  private final void collectionInteger(@Observes final Collection<Integer> payload) {

    System.out.println("*** collection Integer");

  }

  private final void collectionNumber(@Observes final Collection<Number> payload) {

    System.out.println("*** collection Number");

  }

  @Test

  public void testContainerStartup() {

    final SeContainerInitializer initializer = SeContainerInitializer.newInstance();

    assertNotNull(initializer);

    initializer.disableDiscovery();

    initializer.addBeanClasses(this.getClass());

    try (final SeContainer container = initializer.initialize()) {

      assertNotNull(container);

      final BeanManager beanManager = container.getBeanManager();

      assertNotNull(beanManager);

      final TypeLiteral<Collection<? extends Number>> literal = new TypeLiteral<Collection<? extends Number>>() {

          private static final long serialVersionUID = 1L;

        };

      final Event<Collection<? extends Number>> broadcaster = beanManager.getEvent().select(literal);

      assertNotNull(broadcaster);

      final Collection<? extends Number> payload = Collections.singleton(Integer.valueOf(1));

      broadcaster.fire(payload);

    }

  }

In this case, only the first observer method prints anything.

The main thing that I'm struggling with is that at the point where I would like to fire my payload, all I know is that it is, effectively, Collection<? extends Number>, even though it might "actually" be Set<Integer> (as in the example above).

So my TypeLiteral has to be TypeLiteral<Collection<? extends Number>>, unless I'm missing something.

And if it has to be TypeLiteral<Collection<? extends Number>>, then I don't know how to fire the payload in such a way that an observer of, say, Collection<? extends Integer> or Collection<Integer> would be notified.

[manovotn]

Hi Laird,

I've added an answer to your SO crosspost, so in order not to dulicate info, here is the link.

I am still puzzled by the last case and if I will try to get more information about that.