How to ignore any http content headers on Spring @RestController?

Question

I have some webservice endpoints that should offer json data by default. Therefore configuring as follows:

@Configuration
public class ContentNegotiationConfiguration implements WebMvcConfigurer {
    @Override
    public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
        configurer.defaultContentType(MediaType.APPLICATION_JSON);
    }
}

Problem: now I want to create an endpoint that offers a file download (thus is not json).

@RestController
public class FileServlet {
   @GetMapping(value = "/docs/{filename}", consumes = MediaType.ALL_VALUE, produces = APPLICATION_OCTET_STREAM_VALUE)
   public Object download(@Pathvariable filename) {
          File file = fileservice.resolve(filename);
          return new FileSystemResource(file);
   }
}

Accessing this endpoint from the browser works fine. I can download the files.

But: when using native clients that are not setting any http headers like content-type, accept-header etc, the access fails with:

WARN o.s.w.s.m.m.a.ExceptionHandlerExceptionResolver: Resolved 
[org.springframework.web.HttpMediaTypeNotAcceptableException:
Could not find acceptable representation]

All of them result in the exception:

curl localhost:8080/docs/testfile.txt
curl -O localhost:8080/docs/testfile.txt
wget localhost:8080/docs/testfile.txt

This is probably because I set the default content type to json above in ContentNegotiationConfiguration. I cannot change that due to all the other endpoints that should be json by default.

Question: how can I explicit ignore that default json setting on that single endpoint, and always just offer the download stream?

Answer 1

With the hint from @M. Deinum, I got it working as follows:

 @GetMapping(value = "/docs/{filename}")
 public void download(@Pathvariable filename) {
    FileSystemResource file = new FileSystemResource(fileservice.resolve(filename));
    rsp.setHeader("Content-Disposition", "attachment; filename=" + file.getFilename());

    ResourceHttpMessageConverter handler = new ResourceHttpMessageConverter();
    handler.write(file, MediaType.APPLICATION_OCTET_STREAM, new ServletServerHttpResponse(rsp));
 }

That way writing directly to the stream bypassing the content negotiation, while still relying on the Spring class ResourceHttpMessageConverter for not having to implement the response writer myself.