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?

Note that you may specify headers with curl, see here : https://stackoverflow.com/questions/7172784/how-to-post-json-data-with-curl-from-terminal-commandline-to-test-spring-rest — Arnaud, Oct 31 '18 at 11:19
Well but I don't want having to set any headers to request the file for download! They should just be ignored. Also curl is just an example here. It could as well be `wget`, any php or java client, whatsoever. — membersound, Oct 31 '18 at 11:22
Stream the result yourself, including the headers, instead of letting Spring do it. — M. Deinum, Oct 31 '18 at 12:09
Can you add the full stacktrcae? Because I want to see where the exception originates from. — M. Deinum, Oct 31 '18 at 12:43
Sorry, removed my comment. It was caused by still having the `produces` field set. Have a look at my answer, which works as you suggested! — membersound, Oct 31 '18 at 12:48

score 0 · Answer 1 · answered Oct 31 '18 at 12:18

Try custom ContentNegotiationStrategy with AntPathMatcher something like:

@Override
public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
    //  configurer.defaultContentType(MediaType.APPLICATION_JSON,MediaType.APPLICATION_OCTET_STREAM);


    configurer.defaultContentTypeStrategy(
            new ContentNegotiationStrategy() {
                private UrlPathHelper urlPathHelper = new UrlPathHelper();
                AntPathMatcher antPathMatcher = new AntPathMatcher();
                @Override
                public List<MediaType> resolveMediaTypes(NativeWebRequest webRequest) throws HttpMediaTypeNotAcceptableException {
                    HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
                    if (request == null) {
                        return null;
                    }
                    String path = this.urlPathHelper.getLookupPathForRequest(request);
                    if (antPathMatcher.match("/docs/*", path)) {
                        return Collections.singletonList(MediaType.APPLICATION_OCTET_STREAM);
                    } else {
                        return Collections.singletonList(MediaType.APPLICATION_JSON);
                    }

                }
            });

}

score 0 · Accepted Answer · answered Oct 31 '18 at 12:50

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.

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

2 Answers2