How do I retrieve Resource object using restTemplate in Spring Boot?

So, basically the title.

I got 2 microservices. One generates and sends a zip file and the other one receives it, then does some magic, converts it to an array[] of bytes and then sends it somewhere else. But it’s just in theory – I coldn’t make it work.

I need to download a Resource (https://docs.spring.io/spring-framework/docs/3.2.x/spring-framework-reference/html/resources.html) that contains InputStream that my generated zip archive is wrapped into. Writing it inside OutputStream of a HttpServletResponse doesn’t work for me since I can’t use it – later on I need to manipulate the file and this approach is for browser download only (?)

So I did this in the first microservice:

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        BufferedOutputStream bos = new BufferedOutputStream(baos);
        ZipOutputStream zos = new ZipOutputStream(bos);
        try {
            zos = service.generateZip(blablabla, zos);

            baos.close();
            bos.close();
            zos.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

        ByteArrayResource resource = new ByteArrayResource(baos.toByteArray());    

        ResponseEntity<Resource> response = ResponseEntity.ok()
                    .contentType(MediaType.parseMediaType("application/zip;charset=UTF-8"))
                    .contentLength(resource.contentLength())
                    .header(HttpHeaders.CONTENT_DISPOSITION,
                            ContentDisposition.parse(format("attachment; filename="doc_%s.zip"", id)).toString())
                    .body(resource);

And this in second:

    public byte[] getZip(DocRequest request) throws IOException {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.parseMediaType("application/zip;charset=UTF-8"));
        headers.setAccept(Collections.singletonList(MediaType.parseMediaType("application/zip;charset=UTF-8")));
        // headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        // headers.setAccept(Collections.singletonList(MediaType.APPLICATION_OCTET_STREAM));

        Resource response = restTemplate.exchange(
                        apiUrl + "/doc/get-zip/" + request.getId(),
                        HttpMethod.GET,
                        new HttpEntity<>(null, headers),
                        Resource.class)
                .getBody();

        return (response != null) ? IOUtils.toByteArray(response.getInputStream()) : null;
    }

also added ResourceHttpMessageConverter to a restTemplate to configs of both microservices:

        MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
        converter.setSupportedMediaTypes(Collections.singletonList(MediaType.ALL));
        converter.setObjectMapper(objectMapper);

        ResourceHttpMessageConverter resourceConverter = new ResourceHttpMessageConverter();
        resourceConverter.setSupportedMediaTypes(Collections.singletonList(MediaType.ALL));

        return builder.interceptors(...)
                .messageConverters(resourceConverter, converter)
                .configure(restTemplate);

Without them I get an error which looks like this:

{"method":"POST","exceptionName":"RestClientException","detail":"Error while extracting response for type [interface org.springframework.core.io.Resource] and content type [application/octet-stream]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Invalid UTF-8 middle byte 0x59; nested exception is com.fasterxml.jackson.core.JsonParseException: Invalid UTF-8 middle byte 0x59n at [Source: (ByteArrayInputStream); line: 1, column: 13]"}

{"method":"POST","exceptionName":"RestClientException","detail":"Error while extracting response for type [interface org.springframework.core.io.Resource] and content type [application/zip;charset=UTF-8]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Invalid UTF-8 start byte 0x91; nested exception is com.fasterxml.jackson.core.JsonParseException: Invalid UTF-8 start byte 0x91n at [Source: (ByteArrayInputStream); line: 1, column: 12]"}

depending on contentType (application/octet-stream and application/zip (application/zip;charset=UTF-8) respectively).

After I added ResourceHttpMessageConverter it now gives me

{"method":"POST","exceptionName":"RestClientException","detail":"Error while extracting response for type [interface org.springframework.core.io.Resource] and content type [application/octet-stream]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Unrecognized token 'PKu0003..': was expecting ('true', 'false' or 'null'); nested exception is com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'PKu0003...': was expecting ('true', 'false' or 'null')n at [Source: (ByteArrayInputStream); line: 1, column: 28]"}

Maybe I am using something wrong? Any advice would be appreciated. Thank you in advance

Answer

Ended up encoding byte array to base64 string then sent it as

return ResponseEntity.ok().body(Base64Utils.encodeToString(baos.toByteArray()));

Then in my receiving microservice I added the following to my restTemplate config:

// idk if it's need to put StringHttpMessageConverter first in the list, but I did it just in case
List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();
messageConverters.add(new StringHttpMessageConverter());
messageConverters.add(new MappingJackson2HttpMessageConverter());
restTemplate.setMessageConverters(messageConverters);

And it worked!

Don’t know if it’s right, but maybe someone will find it helpful

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Answer