David V David V - 15 days ago 9
Java Question

Return a stream with Spring MVC's ResponseEntity

I have a Spring MVC method which returns a

ResponseEntity
. Depending on the specific data retrieved, it sometimes needs to return a stream of data to the user. Other times it will return something other than a stream, and sometimes a redirect. I most definitely want this to be a stream and not a byte array since it can be large.

Currently, I return the stream using the following snippet of code:

HttpHeaders httpHeaders = createHttpHeaders();
IOUtils.copy(inputStream, httpServletResponse.getOutputStream());

return new ResponseEntity(httpHeaders, HttpStatus.OK);


Unfortunately, this does not allow the Spring
HttpHeaders
data to actually populate the HTTP Headers in the response. This makes sense since my code writes to the
OutputStream
before Spring receives the
ResponseEntity
.

It would be very nice to somehow return a
ResponseEntity
with an
InputStream
an let Spring handle it. It also would parallel the other paths of my function where I can successfully return a
ResponseEntity
. Is there anyway I can accomplish this with Spring?




Also, I did try returning the
InputStream
in the
ResponseEntity
just to see if Spring would accept it.

return new ResponseEntity(inputStream, httpHeaders, HttpStatus.OK);


But it throws this exception:

org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation





I can get my function to work by setting everything on the
HttpServletResponse
directly, but I would like to do this only with Spring.

Answer

Spring's InputStreamResource works well. You need to set the Content-Length manually, or it appears that Spring attempts to read the stream to obtain the Content-Length.

InputStreamResource inputStreamResource = new InputStreamResource(inputStream);
httpHeaders.setContentLength(contentLengthOfStream);
return new ResponseEntity(inputStreamResource, httpHeaders, HttpStatus.OK);

I never found any web pages suggesting using this class. I only guessed it because I noticed there were a few suggestions for using ByteArrayResource.