The java.util.Set does not work as @RequestParam in Greenwich.SR1

[Ziemowit]

After upgrade:

• from spring-boot 2.0.8.RELEASE / spring-cloud Finchley.SR3
• to spring-boot 2.1.3.RELEASE / spring-cloud Greenwich.SR1

our @FeignClient has an issue with passing java.util.Set as @RequestParam

@RequestMapping("foo/{applicationId}/tools")
@FeignClient(name = "service-foo")
public interface ProxyShareTool {

  @GetMapping("/findDefaultIfVisibleByIds")
  Map<Long, TranslatedShareToolDTO> findVisible(@PathVariable("applicationId") String appId,
                                                @RequestParam("waveIds[]") Set<Long> waveIds,
                                                @RequestParam("lang") String lang);
}

After decode generated request we see following:

findDefaultIfVisibleByIds?waveIds[]={waveIds[]}&lang=en

So seems that instead of ids following text was inserted

{waveIds[]}

[sN0wpeak]

I have same problem in Greenwich.RELEASE. I use @RequestParam("ids[]") List<Integer> ids as params.
result is:

{"timestamp":"2019-03-18T14:30:35.821+0000","status":400,"error":"Bad Request","message":"Failed to convert value of type 'java.lang.String' to required type 'java.util.List'; nested exception is java.lang.NumberFormatException: For input string: \"{ids[]}\"","path":"/"}

I found it caused by not matched Expression in Expressions.
Shall we put the (Pattern.compile("(\\w[-\\w.]*[ ]*[\\[]*[\\]]*)(:(.+))?"), Expressions.SimpleExpression.class) or create a new Expression in the expressions?

[OlgaMaciaszek]

Hello, @Ziemowit @mm23504570 Thanks for reporting this. I have triaged it and it appears to be an actual bug, however, its root cause can be found in the OpenFeign library. I have created this issue and will be back here with any updates as soon as possible.

[Ziemowit]

Hooray!!! :)