Spring Cloud Open Feign: Decoder for ByteArrayResource - arrays

Question

I have a Spring Boot Rest End Point defined in an interface to download an image
#GetMapping(value = "/{name}")
ResponseEntity<ByteArrayResource> getFileByName(#PathVariable("name") String name);
And I use Feign Builder to invoke this end point.
Feign.builder()
.client(new ApacheHttpClient())
.contract(new SpringMvcContract())
.decoder(new JacksonDecoder())
.encoder(new JacksonEncoder())
.target(clazz, url)
On invoking, I get below error
com.fasterxml.jackson.core.JsonParseException: Unexpected character ('�' (code 65533 / 0xfffd)): expected a valid value (number, String, array, object, 'true', 'false' or 'null')
at [Source: (BufferedReader); line: 1, column: 2]
When I try to invoke the end point directly from Insomnia, it works fine. But fails through Feign Builder. The response content type is image/jpeg
Is there any specific decoder in feign to handle ByteArrayResource? I tried ResponseEntityDecoder, StreamDecoder and JacksonDecoder. None of it works.
On debugging, I see that Jackson ObjectMapper readValue fails. I tried changing the return type from ByteArraySource to byte[], didn't work either.
Any help?

Answer 1

I wrote my own little decoder and the problem was resolved. Below is the decoder
private Decoder byteArrayResourceDecoder() {
Decoder decoder = (response, type) -> {
if (type instanceof Class && ByteArrayResource.class.isAssignableFrom((Class) type)) {
return StreamUtils.copyToByteArray(response.body().asInputStream());
}
return new JacksonDecoder().decode(response, type);
};
return new ResponseEntityDecoder(decoder);
}
Hope this template helps others who has similar issues. Would have expected Feign to have decoder that supports all return types.

Answer 2

Thanks Maz - your solution helped me.
I modified your solution for my needs to read Spring StreamingResponseBody
1.) Create the decoder wrapper that either returns JacksonDecoder (Default) or reads the responsebody into a byte array.
Decoder decoder = (response, type) -> {
Map<String, Collection<String>> headers = response.headers();
Collection<String> contentType = null;
for (String x : headers.keySet()){
if ("content-type".equals(x.toLowerCase())){
contentType = headers.get(x);
}
}
if (contentType == null || contentType.stream().filter(x -> x.contains("application/json")).findFirst().isPresent()) {
return new JacksonDecoder(getMapper()).decode(response, type);
}
InputStream initialStream = response.body().asInputStream();
byte[] buffer = new byte[512];
byte[] result = null;
try(ByteArrayOutputStream out = new ByteArrayOutputStream()) {
try {
int length = 0;
while ((length = initialStream.read(buffer)) != -1) {
out.write(buffer, 0, length);
}
} finally {
out.flush();
}
result = out.toByteArray();
} finally {
initialStream.close();
}
return result;
};
2.) Use the custom decoder with the Feign.Builder
Feign.Builder builder = Feign.builder()
// --
.decoder(decoder)
// --
openfeignfeignspringstreamingresponsebody