Is there a change to return a png file like response.png instead of response.bin

Question

The aim of my code is to retrieve an image from a third-party service.

I struggled a little for endpoint of download to work and only partially succeeded. When I call the endpoint via postman the answer is a .bin file, but what I need is to have a .png file. The greatest success is being able to get a .png file being able to customize the name as well. But personalization of the is not strictly necessary.

The project is built with the initializer and has the following dependencies:

• spring-boot-starter-web;
• lombok
• spring-boot-starter-webflux
• reactor-spring

Below is the source code of my endpoint:

@GetMapping("/retrieve-image")
public Mono<byte[]> retrieveImage(ImageRequest request) throws ExecutionException, InterruptedException, IOException {
    MultiValueMap<String, String> queryParams = new LinkedMultiValueMap<>();
    queryParams.add("attribute", request.getAttribute()); // fake for query string setting.
    Mono<byte[]> image = webClient
            .get()
            .uri(uriBuilder -> uriBuilder
                    .path(Endpoint.THIRD_PARTY_SERVICE_URI)
                    .queryParams(queryParams)
                    .build())
            .accept(MediaType.valueOf(String.valueOf(MediaType.IMAGE_PNG)))
            .exchange()
            .flatMap(clientResponse -> clientResponse.bodyToMono(byte[].class)
                    .doOnSuccess(body -> {
                        if (clientResponse.statusCode().isError()) {
                            log.error("HttpStatusCode = {}", clientResponse.statusCode());
                            log.error("HttpHeaders = {}", clientResponse.headers().asHttpHeaders());
                            log.error("ResponseBody = {}", body);
                        }
                    }));
    return image;
}

Answer 1

You can also add the mime type of the file to the produces section of the @GetMapping annotation, it should look something like this:

@GetMapping(path = "/retrieve-image",
        produces = "image/png")

Additionally, instead of returning a Mono<byte[]>, you can wrap your response in a ResponseEntity<Resource>. This gives you the possibility to add Headers and tell the browser the name of your file. For example:

HttpHeaders header = new HttpHeaders();
header.add(HttpHeaders.CONTENT_DISPOSITION,
        "attachment; filename=image.png");
header.add("Access-Control-Expose-Headers", "Content-Disposition");

return ResponseEntity.ok().
        .headers(header)
        .contentLength(Files.size(path))
        .body(<<YOUR_FILE_HERE>>);

One last thought: If you add both spring-boot-starter-web and spring-boot-starter-webflux to your dependencies, the app will work, but it doesn't use Netty from Webflux, instead the usual Tomcat. So you don't benefit from the reactive features.