Send MultiValueMap as MultiPartFormData in Feign Client - spring-cloud-feign

Question

I am trying to convert the below kotlin code from RestTemplate to Feign client. The rest template code sends multiValueMap as request with content-type header multipart/form-data and consumes JSON object as response.
RestTemplate Code:
var headers = HttpHeaders()
headers.contentType = MediaType.MULTIPART_FORM_DATA
headers.add("custom-header", "value")
val body: MultiValueMap<String, Any> = LinkedMultiValueMap()
body.add("field1", "value1")
body.add("field2", "value2")
val requestEntity = HttpEntity(body, headers)
return restTemplate.postForEntity("https://enmf7tx8y37x.x.pipedream.net/", requestEntity, Object::class.java)
In this case the request is sent as below:
Headers:
Host: enmf7tx8y37x.x.pipedream.net
X-Amzn-Trace-Id: Root=1-6303ecb2-19a833a044ab3bf83f74f256
Content-Length: 342
Accept: application/xml, text/xml, application/json, application/*+xml, application/*+json
Content-Type: multipart/form-data;boundary=_MtEGFIF4XK_aOU8QsXstQuCliV1-llj
custom-header: value
X-B3-TraceId: a67561ec329f9a16
X-B3-SpanId: a6cc94e403bfe318
X-B3-ParentSpanId: a67561ec329f9a16
X-B3-Sampled: 1
User-Agent: Apache-HttpClient/4.5.13 (Java/17.0.3)
Accept-Encoding: gzip,deflate
Body:
--_MtEGFIF4XK_aOU8QsXstQuCliV1-llj
Content-Disposition: form-data; name="field1"
Content-Type: text/plain;charset=UTF-8
Content-Length: 6
value1
--_MtEGFIF4XK_aOU8QsXstQuCliV1-llj
Content-Disposition: form-data; name="field2"
Content-Type: text/plain;charset=UTF-8
Content-Length: 6
value2
--_MtEGFIF4XK_aOU8QsXstQuCliV1-llj--
I tried to do the same in Feign client:
code:
/*val headers = HttpHeaders()
headers.contentType = MediaType.MULTIPART_FORM_DATA
headers.add("custom-header", "value")*/
val body: MultiValueMap<String, Any> = LinkedMultiValueMap()
body.add("field1", "value1")
body.add("field2", "value2")
val result = testClient.test("value", body)
Feign Client:
#FeignClient(
value = "testClient",
url = "https://enmf7tx8y37x.x.pipedream.net/"
)
interface TestClient {
#PostMapping(
consumes = [MediaType.MULTIPART_FORM_DATA_VALUE],
produces = [MediaType.APPLICATION_JSON_VALUE]
)
fun test(
#RequestHeader(value = "custom-header") customHeader: String,
#RequestPart("request") request: MultiValueMap<String, Any>
): ResponseEntity<Object>
}
The header are fine but no value present in the body.
Header:
Host: enmf7tx8y37x.x.pipedream.net
X-Amzn-Trace-Id: Root=1-6303ef0f-78c869881a5b27d0707eab9e
Content-Length: 17
Accept: application/json
Authorization: Basic aHlwb2xhYjp0ZXN0c211cmY=
Content-Type: multipart/form-data; charset=UTF-8; boundary=182c75dd399
custom-header: value
X-B3-TraceId: 2989eb4f12e3d417
X-B3-SpanId: 23414bcdf365784c
X-B3-ParentSpanId: 2989eb4f12e3d417
X-B3-Sampled: 1
User-Agent: Java/17.0.3
Body:
--182c75dd399--
I had to add consumes value as multipart/form-data instead of json to get the right header values for Accept and Content-Type.
How can I populate the request using Feign client? If the #RequestPart is String then the value is sent in the body but any other data type like multiValueMap, byteArray, etc were not working

Answer 1

In feign client you cannot use MultiValueMap directly. You have to use MultipartFile datatype for bytearray and for the remaining metadata fields you need to mention each one as a separate argument in the method. Then FeignClient will generate the same request like the one you showed when using RestTemplate.
import org.springframework.cloud.openfeign.FeignClient
import org.springframework.web.bind.annotation.PostMapping
import org.springframework.http.MediaType
import org.springframework.http.ResponseEntity
import org.springframework.web.bind.annotation.RequestHeader
import org.springframework.web.bind.annotation.RequestPart
import org.springframework.web.multipart.MultipartFile
#FeignClient(
value = "testClient",
url = "https://enmf7tx8y37x.x.pipedream.net/"
)
interface TestClient {
#PostMapping(
consumes = [MediaType.MULTIPART_FORM_DATA_VALUE],
produces = [MediaType.APPLICATION_JSON_VALUE]
)
fun test(
#RequestHeader(value = "custom-header") customHeader: String,
#RequestPart(name = "file") file: MultipartFile,
#RequestPart(name = "field1") field1: String
): ResponseEntity<Object>
}
code sample for How to create MultiPartFile:
import org.springframework.mock.web.MockMultipartFile
//val multipartFile: MultipartFile = MockMultipartFile("filename", byteArray)
val multipartFile: MultipartFile = MockMultipartFile("filename", "filename", "content type like application/pdf", byteArray)