Spring Framework 4.2 introduced support for aliases between annotation
attributes that fall into the following two categories.
1) Alias pairs: two attributes in the same annotation that use
@AliasFor to declare that they are explicit aliases for each other.
2) Meta-annotation attribute overrides: an attribute in one annotation
uses @AliasFor to declare that it is an explicit override of an
attribute in a meta-annotation.
However, the existing functionality fails to support the case where two
attributes in the same annotation both use @AliasFor to declare that
they are both explicit overrides of the same attribute in the same
meta-annotation. In such scenarios, one would intuitively assume that
two such attributes would be treated as "implicit" aliases for each
other, analogous to the existing support for explicit alias pairs.
Furthermore, an annotation may potentially declare multiple aliases
that are effectively a set of implicit aliases for each other.
This commit introduces support for implicit aliases configured via
@AliasFor through an extensive overhaul of the support for alias
lookups, validation, etc. Specifically, this commit includes the
following.
- Introduced isAnnotationMetaPresent() in AnnotationUtils.
- Introduced private AliasDescriptor class in AnnotationUtils in order
to encapsulate the parsing, validation, and comparison of both
explicit and implicit aliases configured via @AliasFor.
- Switched from single values for alias names to lists of alias names.
- Renamed getAliasedAttributeName() to getAliasedAttributeNames() in
AnnotationUtils.
- Converted alias map to contain lists of aliases in AnnotationUtils.
- Refactored the following to support multiple implicit aliases:
getRequiredAttributeWithAlias() in AnnotationAttributes,
AbstractAliasAwareAnnotationAttributeExtractor,
MapAnnotationAttributeExtractor, MergedAnnotationAttributesProcessor
in AnnotatedElementUtils, and postProcessAnnotationAttributes() in
AnnotationUtils.
- Introduced numerous tests for implicit alias support, including
AbstractAliasAwareAnnotationAttributeExtractorTestCase,
DefaultAnnotationAttributeExtractorTests, and
MapAnnotationAttributeExtractorTests.
- Updated Javadoc in @AliasFor regarding implicit aliases and in
AnnotationUtils regarding "meta-present".
Issue: SPR-13345
d40a35ba5c