ApplicationListener no longer invoked for generic ApplicationEvent with 6.2.0

[denAbramoff]

Hello!

I have simple interface like this:

public interface ITest
{
}

and the simple event:

public class TestEvent<T extends ITest> extends ApplicationEvent
{
    public TestEvent(Object source)
    {
        super(source);
    }
}

and two listeners:

@Component
public class MethodListener
{
    @EventListener
    public void handleTestEvent(TestEvent<ITest> iTest)
    {
        System.out.println(this.getClass() + " DONE!");
    }
}

@Component
public class SimpleTestListener implements ApplicationListener<TestEvent<ITest>>
{
    @Override
    public void onApplicationEvent(TestEvent<ITest> event)
    {
        System.out.println(this.getClass() + " DONE!");
    }
}

and when i trying to send an event via the spring context like this:

public class MySpringApplication
{
    public static void main(String[] args)
    {
        ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        context.publishEvent(new TestEvent<>(""));
    }
}

i have different result in depends on the version Spring. When i use Spring 6.2 i can see in the log this:

class ... MethodListener DONE!

when i use Spring 6.1.15 i see both results:

class ...SimpleTestListener DONE!
class ...MethodListener DONE!

I guess it's a bug.

[sbrannen]

If you make the parameterized type for TestEvent concrete as follows, you get the expected result.

context.publishEvent(new TestEvent<ITest>("") {});

Note the use of {} which makes it a subclass of TestEvent bound to ITest instead of T.

So this might have been a bug fix instead of a bug/regression.

@jhoeller, thoughts?

[sbrannen]

The following all-in-one test class demonstrates this.

@SpringJUnitConfig
class GenericApplicationEventListenerTests {

	@Test
	void test(ApplicationContext context) {
		context.publishEvent(new TestEvent<ITest>("") {
		});
	}


	@Configuration
	@Import({MethodListener.class, SimpleTestListener.class})
	static class Config {
	}

	interface ITest {
	}

	static class TestEvent<T extends ITest> extends ApplicationEvent {

		TestEvent(Object source) {
			super(source);
		}
	}

	static class MethodListener {

		@EventListener
		public void handleTestEvent(TestEvent<ITest> iTest) {
			System.err.println(getClass().getSimpleName() + " DONE!");
		}
	}

	static class SimpleTestListener implements ApplicationListener<TestEvent<ITest>> {

		@Override
		public void onApplicationEvent(TestEvent<ITest> event) {
			System.err.println(getClass().getSimpleName() + " DONE!");
		}
	}

}

Output:

SimpleTestListener DONE!
MethodListener DONE!

[anaconda875]

Hi @sbrannen, I'm a Java developer who want to contribute to the framework. How can I get this issue/task assigned (to me)? Thanks

[denAbramoff]

@sbrannen thanks for your reaction! Yep, this version works:

context.publishEvent(new TestEvent<ITest>("") {});

But it's not convenient and there are a lot of places where old version works.

And there is also one weird case, if i add "? extends" my listenerer will work:

@Configuration
public class WildcardSimpleTestListener implements ApplicationListener<TestEvent<? extends ITest>>
{
    @Override
    public void onApplicationEvent(TestEvent<? extends ITest> event)
    {
        System.out.println(this.getClass() + " DONE!");
    }
}

It works on Spring 6.2!

class ...WildcardSimpleTestListener$$SpringCGLIB$$0 DONE!

[theigl]

Probably related to #33968.

[sbrannen]

Thanks for the feedback, @denAbramoff.

In light of the above, I believe this is a regression, and we'll look into it.

@jhoeller, I have tentatively assigned this to you due to your work on related issues.

Potentially Related Issues

• Invalid instance injected for generic type in case of partial type variable [SPR-16179] #20727
• Add support for resolving multiple bounds in type variables #22902
• Injection points with wildcards are not as lenient as before #32327
• Generic type resolution broken in 6.2.0 (possible regression of #24963) #33968

[sbrannen]

Hi @sbrannen, I'm a Java developer who want to contribute to the framework. How can I get this issue/task assigned (to me)? Thanks

Hi @anaconda875,

Thanks for the offer!

As you can see above, I've assigned to this @jhoeller, since he has done the most recent work in this area. However, if you feel confident in fixing this regression, please post your ideas here first before submitting a PR.

[anaconda875]

Hi @sbrannen ,
In Spring Core , ResolvableType.isAssignableFrom line 336-337:

WildcardBounds ourBounds = WildcardBounds.get(this);    //ourBounds IS NULL SINCE this PASSED TO WildcardBounds.get() IS A ResolvableType OF ITest
WildcardBounds typeBounds = WildcardBounds.get(other);  //typeBounds IS NOT NULL SINCE other PASSED TO WildcardBounds.get() IS ResolvableType OF <T extends ITest>

My proposal:

Inside red circle is newly added.
Plz take a look!! Thanks

[jhoeller]

This turned out to be rather involved, a consequence of the partial generics matching that we do as of 6.2 now where we also take the bounds of an unresolvable type variable into account. The solution that I went with is a rather minimal tweaking of the existing strict flag when we go into nested generics. I hope that this covers the reported case here. @denAbramoff please give an upcoming 6.2.1 snapshot an early try...

@anaconda875 I ended up with a different approach but thanks for the PR in any case!

[sbrannen]

I hope that this covers the reported case here.

I tested with context.publishEvent(new TestEvent<>("")); on main, and that now works as expected.

Thanks, Juergen!