Spring @AliasFor with property for nested annotation

Question

Is it possible to have @AliasFor annotation pass the argument to nested annotation? Something like passing value of name() to nested @Queue annotation inside @RabbitListener? I basically wanted to specify multiple queues with same binding parameters to same exchange, and only vary queue name.

Artem Bilan · Accepted Answer · 2021-11-17 16:30:39Z

1

I don't think you can do that for nested annotations. You probably need to think about having a custom @Queue annotation extension and then used it inside your @SomeListener. But the problem is that @Queue annotation cannot be extended. It has that @Target({}), so it is not possible at the moment.

If you really wish to have such a customization, consider to fix Spring AMQP on the matter via @Target(ANNOTATION_TYPE) and add some tests to demonstrate the feature and contribute it back to the framework.

Unfortunately I don't see the other way to support your request, unless you would go the to declare Queue beans and use just their names in that your custom annotation:

@Retention(RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
@RabbitListener
public @interface MyListener {
    
    @AliasFor(annotation = RabbitListener.class, attribute = "queues")
    String[] queues() default {};
    
}

answered Nov 17, 2021 at 16:30

Artem Bilan

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3 Comments

Gary Russell Over a year ago

One thought I had is we could expose a hook in the bean post processor to allow the user to manipulate the MergedAnnotations before we synthesize the new annotation - e.g. copy the value of a top level attribute into the nested attribute - something like return MergedAnnotations.of(SomeListener.class, updateAttributes(merged.asMap())). I will experiment.

Bojan Vukasovic Over a year ago

Thanks. Just wanted to see if there is a way to do it that way. I guess I can always just define all the beans separately and wire them...

Gary Russell Over a year ago

Prototype here: github.com/garyrussell/spring-amqp/commit/… let me know if providing a hook to allow you to modify the annotation would satisfy your requirements.

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