Provide a mechanism for composed annotations to signal that they want to override attributes [SPR-13448]

[spring-projects-issues]

Dave Syer opened SPR-13448 and commented

AnnotatedElementUtils is now available for processing merged (overridden) attributes from meta-annotated custom annotations, but Spring doesn't use it uniformly (because of performance concerns). The one that bit me was an ImportBeanDefinitionRegistrar where the annotation was a custom one and the AnnotationMetadata that is passed in does not contain the overridden/inherited values.

The reason, it turns out, is that StandardAnnotationMetadata, while it uses AnnotatedElementUtils, explicitly chooses not to get the overridden attributes by invoking getAllAnnotationAttributes() instead of getMergedAnnotationAttributes() (and this is all that is directly available to the ImportBeanDefinitionRegistrar).

Maybe there's a way to address the performance concerns and use the deeper AnnotatedElementUtils.getMergedAnnotationAttributes() utility method(s) only if the user signals that the annotation needs to be processed this way -- for example, by introducing an annotation such as @Mergeable (or an explicit @AliasFor on the attribute).

See also: #18020

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Affects: 4.2 GA

Issue Links:

• Use AnnotatedElementUtils instead of AnnotationUtils wherever feasible [SPR-13440] #18020 Use AnnotatedElementUtils instead of AnnotationUtils wherever feasible
• @AliasFor is needed on all attributes (even if they have the same name as the "parent") [SPR-13554] #18130 @AliasFor is needed on all attributes (even if they have the same name as the "parent")
• Support @ResponseStatus as a merged composed annotation [SPR-13441] #18021 Support @ResponseStatus as a merged composed annotation

0 votes, 6 watchers

[spring-projects-issues]

Dave Syer commented

There is a workaround for my current specific issue (because I control the ImportBeanDefinitionRegistrar), which is to use the more powerful method in AnnotatedElementUtils explicitly:

public class SomethingRegistrar implements ImportBeanDefinitionRegistrar {

	@Override
	public void registerBeanDefinitions(AnnotationMetadata metadata,
			BeanDefinitionRegistry registry) {
		AnnotationAttributes attrs = AnnotatedElementUtils.getMergedAnnotationAttributes(
				ClassUtils.resolveClassName(metadata.getClassName(), null),
				EnableSomething.class);
		for (Class<?> type : collectClasses(attrs.get("value"))) {
			BeanDefinition beanDefinition = new RootBeanDefinition(type);
			registry.registerBeanDefinition("something", beanDefinition);
		}
	}

N.B. the custom annotation has to use @AliasFor on all its inherited attributes for this to work.

[spring-projects-issues]

Sam Brannen commented

Dave Syer,

I'm glad you found a work-around for the time being.

FYI: please note that getAllAnnotationAttributes() and getMergedAnnotationAttributes() actually have quite different semantics. getAllAnnotationAttributes() aggregates attributes across all annotations present above the annotated element; whereas, getMergedAnnotationAttributes() only merges attributes from a single branch in the annotation hierarchy.

This subtlety may not have any impact on your particular use case, but...

The reason I mention this difference is that getAllAnnotationAttributes() will find multiple instances of the target annotation (if present), but getMergedAnnotationAttributes() will only find one instance of the target annotation, ignoring any other instances of the target annotation that may be present. Typically, only @Profile and @Conditional require the "aggregate" semantics.

Make sense?

N.B. the custom annotation has to use @AliasFor on all its inherited attributes for this to work.

What do you mean by "all" in this context?

Are you saying that convention-based attribute overrides do not work? If so, then that's a bug, and please report it.

Cheers,

Sam

[spring-projects-issues]

Bulk closing outdated, unresolved issues. Please, reopen if still relevant.