Explicit attribute overrides configured via @AliasFor not supported for components picked up via component scanning

[brucelwl]

I have a longer set of annotation attributes, so I use @AliasFor to set up a short annotation. If the new annotation is set on the boot class, the value of the annotation attributes can be obtained, but the value of the annotation attributes can not be obtained on the non-boot class
Maybe if you look at my demo, you can get a clearer understanding of what I mean.
https://github.com/brucelwl/demo

[sbrannen]

Thanks for raising the issue.

In your example, it turns out that @AliasFor is not honored for attribute override support in a meta-annotation when AnnotationMetadataReadingVisitor is the concrete implementation type for the AnnotationMetadata importingClassMetadata argument supplied to your registerBeanDefinitions() implementation.

In contrast, when the concrete implementation type is StandardAnnotationMetadata, your code works as expected.

So that at least explains what it is going on.

I don't yet have a workaround or solution to your problem, but we will continue to investigate.

[sbrannen]

@brucelwl, one way to circumvent the issue is to force the loading of @Configuration classes discovered via component scanning.

If you're OK with eagerly forcing the loading of such classes, the following should work for you in GitConfigBeanDefinitionRegistrar.

Basically, the goal in the following code is to:

1. retrieve the fully qualified class name of the @Configuration class from the supplied metadata
2. eagerly load the @Configuration class using reflection via ClassUtils
3. use AnnotatedElementUtils for full support of @AliasFor, including support for attribute overrides in meta-annotations.

Class<?> clazz = null;
try {
	String className = importingClassMetadata.getClassName();
	clazz = ClassUtils.forName(className, null);
}
catch (ClassNotFoundException ex) {
	throw new RuntimeException(ex);
}
EnableGitVersionControlConfig anno =
	AnnotatedElementUtils.findMergedAnnotation(clazz, EnableGitVersionControlConfig.class);

logger.info("*** serverAddress={}", anno.serverAddress());
logger.info("*** targetBranch={}", anno.targetBranch());

When I execute your tests with the above change, I see the expected log output.

Please let me know if this workaround works for you!

Thanks,

Sam

[brucelwl]

@sbrannen Thank you very much for your reply. Your solution can solve my problem. I have another similar solution.

public class GitConfigBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {

    private static final Logger logger = LoggerFactory.getLogger(GitConfigBeanDefinitionRegistrar.class);

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        String className = importingClassMetadata.getClassName();
        Class<?> aClass = null;
        try {
            aClass = ClassUtils.forName(className, null);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        StandardAnnotationMetadata metadata = new StandardAnnotationMetadata(aClass, true);
        AnnotationAttributes annotationAttributes = AnnotationAttributes.fromMap(
                metadata.getAnnotationAttributes(EnableGitVersionControlConfig.class.getName()));
        logger.info("serverAddress={}", annotationAttributes.getString("serverAddress"));
        logger.info("targetBranch={}", annotationAttributes.getString("targetBranch"));
    }
}

[sbrannen]

@brucelwl, thank you for the confirmation! I am glad to know that works for you.

FWIW, the behavior you described is a known deficiency.

Fortunately, @philwebb resolved this issue for the upcoming Spring Framework 5.2 release. This was achieved by the introduction of a new SimpleAnnotationMetadata class that is used behind the scenes for components picked up via component scanning. SimpleAnnotationMetadata uses the new MergedAnnotations API which provides full support for @AliasFor within annotation hierarchies, even for metadata sourced from ASM.

I have therefore changed the title of this issue to reflect the known deficiency, and I've assigned this issue to 5.2 so that others know that this has been addressed.

Thanks again, @philwebb, for SimpleAnnotationMetadata and (unwittingly?) fixing this issue!