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;
}

AFAIK, the `spring-web` is not recommended to use with `spring-webflux` in the same app. https://stackoverflow.com/questions/53883037/can-i-use-springmvc-and-webflux-together — Vladimir Shefer, Oct 01 '20 at 11:44
https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/web-reactive.html#webflux . a cite from the documentation: If you have a Spring MVC application with calls to remote services, try the reactive WebClient. You can return reactive types (Reactor, RxJava, or other) directly from Spring MVC controller methods. @VladimirShefer — Stoic Lion, Oct 01 '20 at 12:08
What do you mean by "pear tree" and what is "call the pear by mail"? — meberhard, Oct 02 '20 at 13:38

score 1 · Accepted Answer · answered Oct 02 '20 at 14:32

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.

thanks for the fix. in my endpoint I use Mono<>, with pojo or byte[]. Can you write the whole endpoint in your example? what are the benefits of your solution? .. I'm writing a web server with rest controller, but I need WebClient to do call to third-party service; RestTemplate is very old and unfit... how would you rearrange dependencies? What are the benefits? thanks. — Stoic Lion, Oct 06 '20 at 10:32

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

1 Answers1