Allow a single element to override an array attribute in a meta-annotation [SPR-13972]

[spring-projects-issues]

Juergen Hoeller opened SPR-13972 and commented

Overview

In 4.2, aliased annotation attribute types must match exactly. However, it is rather common in Java for single element values to be specified for an array attribute: Reflecting this in custom annotation design, it would be nice for a custom annotation to be able to declare a single element only, aliasing a meta-annotation attribute which was originally declared as an array, e.g. in a custom @PropertySource variant with a single String value.

Deliverables

1. Allow for a single element overriding an array attribute in a meta-annotation by convention.
   • See findMergedAnnotationAttributesWithSingleElementOverridingAnArrayViaConvention() in AnnotatedElementUtilsTests.
2. Allow for a single element overriding an array attribute in a meta-annotation using @AliasFor.
   • See findMergedAnnotationAttributesWithSingleElementOverridingAnArrayViaAliasFor() in AnnotatedElementUtilsTests.
3. Ensure that the aforementioned overrides are supported in AnnotationAttributes (which is assumed to already be the case but should be verified).
   • See singleElementToSingleElementArrayConversionSupport() in AnnotationAttributesTests.
4. Ensure that the aforementioned overrides are supported in synthesized annotations.
   • See various getMergedAnnotation*WithSingleElementOverridingAnArrayVia*() and findMergedAnnotationWithSingleElementOverridingAnArrayVia*() methods in AnnotatedElementUtilsTests.

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Affects: 4.2.4

Issue Links:

• Introduce common composed annotations for @RequestMapping [SPR-13992] #18565 Introduce common composed annotations for @RequestMapping ("is depended on by")
• Allow the use of custom PropertySource annotations in @Configuration classes [SPR-8963] #13603 Allow the use of custom PropertySource annotations in @Configuration classes
• Introduce common composed annotations for @RequestMapping [SPR-13992] #18565 Introduce common composed annotations for @RequestMapping

[spring-projects-issues]

Sam Brannen commented

Juergen Hoeller, the committed change only works for reading such attributes via the AnnotationAttributes API -- actually, that (little known) feature has been in place for several years in AnnotationAttributes - however, this does not work for synthesized annotations.

When attempting to use this feature with synthesized annotations (e.g., a merged @RequestMapping), we see errors similar to the following (thrown from MapAnnotationAttributeExtractor.enrichAndValidateAttributes()):

java.lang.IllegalArgumentException: Attributes map {name=, value=/get, path=/get, params=[Ljava.lang.String;@6325a3ee, headers=[Ljava.lang.String;@1d16f93d, consumes=[Ljava.lang.String;@67b92f0a, produces=[Ljava.lang.String;@2b9627bc, method=[Lorg.springframework.web.bind.annotation.RequestMethod;@65e2dbf3} returned a value of type [java.lang.String] for attribute 'value', but a value of type [[Ljava.lang.String;] is required as defined by annotation type [org.springframework.web.bind.annotation.RequestMapping].

I have been planning on adding such support for synthesized annotations. So, do you want me to reopen/repurpose this issue or create a separate one to address this?

Cheers,

Sam

[spring-projects-issues]

Juergen Hoeller commented

Let's reopen this one for the wider purpose in the 4.3 timeframe. I only really sneaked it in since I ran into it when coding a recent unit test :-)

Juergen

[spring-projects-issues]

Sam Brannen commented

OK. I'm reopening this issue and assigning it to me in order to address annotations synthesized from maps.

[spring-projects-issues]

Sam Brannen commented

Current work can be viewed in the following branch:

https://github.com/sbrannen/spring-framework/commits/SPR-13972

[spring-projects-issues]

Sam Brannen commented

Pushed to master in the following commit:

eb654dc