Prior to the introduction of the MergedAnnotation API in Spring Framework
5.2, our SynthesizedAnnotationInvocationHandler utilized a cache for
annotation attribute values; whereas, the new
SynthesizedMergedAnnotationInvocationHandler has no such caching in
place.
Issues such as gh-24961 indicate a regression in performance caused by
the lack of such an attribute value cache. For example, the required
attribute in @RequestParam is looked up using the internal meta-model
in the MergedAnnotation API twice per request for each @RequestParam in
a given controller handler method.
This commit reintroduces the attribute value cache to avoid the
unnecessary performance overhead associated with multiple lookups of
the same attribute in a synthesized annotation. This applies not only
to direct attribute method invocations but also to invocations of
equals() and hashCode() on a synthesized annotation.
Note, however, that this commit does NOT address multiple lookups of
annotation attribute values for invocations of toString(). That behavior
currently remains unchanged in the implementation of
org.springframework.core.annotation.TypeMappedAnnotation.toString().
Closes gh-24970
72b1abd226