Spring @RequestParam and controller interface

Question

I'm confused with the behavior of @RequestParam(value="someValue"). In the docs it is said that

When using controller interfaces (e.g. for AOP proxying), make sure to consistently put all your mapping annotations - such as @RequestMapping and @SessionAttributes - on the controller interface rather than on the implementation class.

If I place @RequestParam on my controller interface its value is totally ignored (and therefore mapped value is null if parameter name is different from the received parameter name), but defaultValue and required work ok.

If I place @RequestParam on my controller implementation, everything works fine.

I read this answer, but I cannot understand why some parameters work while others don't and why docs are wrong.

Code example:

interface:

@RequestMapping(method = RequestMethod.GET)
List<MyObject> get(
     //works if parameter in request has name "userName", which is not correct
     @RequestParam(value = "username", required = false) String userName,
     @RequestParam(value = "searchValue", required = false) String searchValue,
     @RequestParam(value = "someId", required = false) Integer someId);

implementation:

@Override
public List<MyObject> get(
        String userName,
        String searchValue,
        Integer someId) {
    return myService.get(userName, searchValue, someId);
}

Answer 1

This finally should be resolved: https://jira.spring.io/browse/SPR-11055?focusedCommentId=160889&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-160889

Juergen Hoeller added a comment - Yesterday

I'm happy to report that this is finally resolved in master now, in time for the 5.1 RC1 release!