Supports annotating parameter annotations like @PathVariable on interface method [SPR-16110]

[spring-projects-issues]

Yanming Zhou opened SPR-16110 and commented

public interface EchoService {
	@RequestMapping(value = "/echo/{name}", method = RequestMethod.POST)
	public String echo(@PathVariable String name);
}

@RestController
public class EchoServiceImpl implements EchoService {
	public String echo(String name) {
		return name;
	}
}

My motivation:
I need annotating @PathVariable and other parameter annotations in interface to create client proxy.

My proposal:
Improve org.springframework.core.MethodParameter to find annotation like AnnotatedElementUtils.findMergedAnnotation() which used by method level annotation like @RequestMapping. If it has side effects, improve RequestResponseBodyMethodProcessor and AbstractNamedValueMethodArgumentResolver directly.

My workaround:
Duplicate Parameter annotations on concrete controller method.

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Issue Links:

• Enable REST controller method parameter annotations on an interface [SPR-11055] #15682 Enable REST controller method parameter annotations on an interface ("duplicates")
• @RequestBody annotation in interface is ignored [SPR-15714] #20270 @RequestBody annotation in interface is ignored