AnnotationUtils.findAnnotation() should support arbitrary levels of meta-annotations [SPR-11448]

[spring-projects-issues]

Sam Brannen opened SPR-11448 and commented

Status Quo

AnnotationUtils.findAnnotation(Class, Class) claims to recursively search through all declared annotations; however, only one level of annotations is supported by the algorithm.

In other words, meta-annotations on meta-annotations will never be found.

Deliverables

1. Alter the search algorithm in AnnotationUtils.findAnnotation(Class, Class) so that arbitrary levels of meta-annotations (e.g., meta-annotations on meta-annotations) are supported.

---

Affects: 3.0 GA

Issue Links:

• Introduce bootstrap strategy in the TestContext framework [SPR-9955] #14588 Introduce bootstrap strategy in the TestContext framework ("is depended on by")
• Introduce aliases for 'value' annotation attributes [SPR-11393] #16020 Introduce aliases for 'value' annotation attributes
• MetaAnnotationUtils should support arbitrary levels of meta-annotations [SPR-11470] #16095 MetaAnnotationUtils should support arbitrary levels of meta-annotations
• TypeDescriptor should support arbitrary levels of meta-annotations [SPR-12793] #17390 TypeDescriptor should support arbitrary levels of meta-annotations

Referenced from: commits 42a3634

[spring-projects-issues]

Sam Brannen commented

Fixed as described in the comments for GitHub commit 42a3634:

Support nested meta-annotations in AnnotationUtils

Prior to this commit, AnnotationUtils.findAnnotation(Class, Class)
claimed to recursively search through annotations; however, only one
level of annotations was supported by the algorithm.

This commit alters the search algorithm so that nested meta-annotations
(i.e., meta-annotations on meta-annotations) are also supported.

[spring-projects-issues]

Juergen Hoeller commented

While this is clearly a mismatch between documentation and behavior, I'd consider it an improvement at this point. The previous behavior was functionally alright for many purposes, it seems, and what we're really doing is to consistently extend our reflection-based search to arbitrary meta-depths now. Our ASM-based annotation checks are a different matter in any case.

In that sense, let's consider this a major improvement, not a minor bug.

Juergen

[spring-projects-issues]

Sam Brannen commented

Juergen, thanks for the feedback!

Here's a bit of additional background information...

This functionality is actually required by #14588. The new @BootstrapWith annotation is used as a meta-annotation on @WebAppConfiguration. So when @WebAppConfiguration is itself used as a meta-annotation on a custom composed annotation, AnnotationUtils.findAnnotation() was not able to find @BootstrapWith before this change. In contrast, AnnotatedElementUtils.getAnnotationAttributes() is able to find @BootstrapWith; however, @BootstrapWith only has a value attribute. Thus using AnnotatedElementUtils is not a solution in such cases since it does not support value attributes.

[spring-projects-issues]

Sam Brannen commented

This issue is conceptually related to #16020 with regard to value attributes on meta-annotations.