I have an endpoint that accepts Set as RequestParam.

@ResponseStatus(OK)
@GetMapping(value = "/people")
public PeopleResponse getPeople(@RequestParam(name = "idType2") Set<String> idsType1) {
    return service.getPeople(idsType1);
}

and this works fine with both types of collection requestparam assignments resulting in 3 elements inside the set. 

localhost:8080/foo/bar/people?idsType1=QWE,RTY,UIO
localhost:8080/foo/bar/people?idsType1=QWE&idsType1=RTY,&idsType1=UIO

However if I move the set into a wrapping class

@Value
@RequiredArgsConstructor
public class IdsType1 {
    Set<String> idsType1;     
}


@ResponseStatus(OK)
@GetMapping(value = "/people")
public PeopleResponse getPeople(
        @Valid IdsType1 idsType1) {
(...)

The comma separated collection ends up being one element containing "QWE,RTY,UIO".

The reason why I wrap my set is because I actually have more parameters and I need to do a complex validation using custom validator. The code above is however the simplest code that unearths the problem that I'm having.

Spring 2.1.1-RELEASE Java 8 openjdk

Comment From: bclozel

I guess the Spring version is really the Spring Boot version; in both cases this version is out of support so please upgrade to a supported version.

In this case, I think you should reach out to StackOverflow to get help as this is really a question for your application and not a bug. You can look into type conversion in Spring MVC, as you probably need to teach Spring how to bind to your specific type.

Thanks!

Comment From: Wolowin

Ok sorry if this issue was misplaced.

In case anyone reaches this thread with similar issue the solution for me was to upgrade SpringBoot to 2.5.0+.