Spring Cloud Feign Client @RequestParam with List parameter creates a wrong request

Question

I have a Spring Clound Feign Client mapping defined as following

@RequestMapping(method = RequestMethod.GET, value = "/search/findByIdIn")
Resources<MyClass> get(@RequestParam("ids") List<Long> ids);

when I call

feignClient.get(Arrays.asList(1L,2L,3L))

according to what I can see in the debugger, the feign-core library forms the following request:

/search/findByIdIn?ids=1&ids=2&ids=3

instead of expected

/search/findByIdIn?ids=1,2,3

which would be correct for the server Spring Data REST endpoint declared in the same way as my Feign client method.

Thus, because of this issue, the request always returns empty set.

I have seen similar question, but it looks like the Feign client was working as I expect back in 2015.

I am using:

spring-cloud-starter-feign version 1.2.4.RELEASE
feign-httpclient version 9.4.0
feign-core version 9.4.0

Is there a way to correct the behaviour and "marry" the Spring Cloud Feign Client with the Spring Data REST defined endpoints?

This may have an impact https://github.com/spring-cloud/spring-cloud-netflix/issues/1526. You might try Dalston.SNAPSHOT, which brings in spring-cloud-netflix 1.3.0.BUILD-SNAPSHOT. If not you should open an issue. — spencergibb, Jan 19 '17 at 16:24
@spencergibb That seems to the behaviour indeed: https://github.com/spring-cloud/spring-cloud-netflix/issues/1634 — Sergey Shcherbakov, Jan 22 '17 at 17:22
Please also see an example project: https://github.com/abinet/demo — Sergey Shcherbakov, Jan 22 '17 at 17:22

score 12 · Accepted Answer · answered Apr 11 '18 at 18:15

I had the same issue with multiple occurence of the parametre instead of the expected comma separated sequence of items. The solution was really simple:

In my feign client I used arrays

feignClient.get(new Long[]{1L,2L,3L})

instead of collection/list:

feignClient.get(Arrays.asList(1L,2L,3L))

score 5 · Answer 2 · answered Sep 16 '20 at 15:10

5

In Feign you can annotate your controller with the following

@CollectionFormat(feign.CollectionFormat.CSV) and it will process collections in

the CSV format findByIdIn?ids=1&ids=2&ids=3

answered Sep 16 '20 at 15:10

prola

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albertocavalcante · Answer 3 · 2021-07-27T00:30:12.250

Thanks @prola for your answer.

Just to add an explicit example, @CollectionFormat(feign.CollectionFormat.CSV) annotation targets a method; you can't apply globally to your Feign Client interface.

So each method will be similar to:

@RequestMapping(value = ["/objects"], method = [RequestMethod.GET])
@CollectionFormat(feign.CollectionFormat.CSV)
fun findById(
    @RequestParam(value = "object.id", required = true) id: String,
    @RequestParam(value = "object.fields", required = false) objectFields: List<String> = DEFAULT_FIELDS_LIST,
    @RequestParam(value = "format") format: String = FORMAT,
): ResponseEntity<ObjectsDTO>

The result will be

/objects?object.fields=size,weight,location

instead of

/objects?object.fields=size&object.fields=weight&object.fields=location

You can also refer to:

This @CollectionFormat(feign.CollectionFormat.CSV) saved my 2 days, thanks a lot — hbellahc, Apr 28 '22 at 12:16
Another option is to declare the CSV format is, for example : @RequestLine( value = "GET "/books?categories={categories}", collectionFormat = CollectionFormat.CSV) — asokan, Jul 06 '22 at 14:45

score 2 · Answer 4 · edited Jul 13 '21 at 21:48

I've just battled with this today, and the solution for me was surprisingly simple.

If you use brackets [] for denoting query array:

Resources<MyClass> get(@RequestParam("ids[]") List<Long> ids);

it will create a request that looks like this

/search/findByIdIn?ids[]=1&ids[]=2&ids[]=3

Most server side frameworks will interpret this as an array. If your server is also in spring then you can pick this up like this

@GetMapping("/search/findByIdIn")
public ResponseEntity findByIdIn(@RequestParam("ids[]") List<Long> ids) { ... }

Just keep in mind that the query has to be encoded, [] gets encoded to %5B%5D.

Spring Cloud Feign Client @RequestParam with List parameter creates a wrong request

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