Downloading file using Spring Webclient, file is empty

Question

I'm supposed to download a ZIP file from 3rd party API. However, when I'm using Spring Webclient I end up with an empty file. Any ideas what I'm doing wrong? What is the proper way to store the content of Flux<DataBuffer> to a file?

Here's my code:

WebClient client = WebClient.builder()
            .clientConnector(new ReactorClientHttpConnector(httpClient1))
            .baseUrl(String.format(FILE_DOWNLOAD_PATH))
            .build();


    WebClient.RequestBodyUriSpec method = client.method(HttpMethod.GET);
    method.header("Authorization", "Bearer " + accessToken);
    final Flux<DataBuffer> dataBufferFlux = method.retrieve().bodyToFlux(DataBuffer.class);

    final Path path = FileSystems.getDefault().getPath("example" + new Random(200).nextInt() + ".zip");

    WritableByteChannel channel = Files.newByteChannel(path, StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE);
    Mono<Path> then = DataBufferUtils.write(dataBufferFlux, channel)
            .map(DataBufferUtils::release)
            .then(Mono.just(path));

UPDATE: The above code is being called directly from main, and then the application shuts down. Could this be an issue?

If that don't throw an exception, the problem is the REST Api you are calling — Adrian Lagartera, Jul 14 '20 at 15:08
@AL it doesn't throw an exception, it just creates an empty .zip file. I'm able to download the file from this API using POSTMAN, so the API itself works just fine — Endrew, Jul 14 '20 at 15:25
As for your update - remember that nothing happens until you subscribe. Usually with spring the framework will subscribe for you, but obviously that doesn't apply if you're not using a framework controlled method. Try calling `block()` on your `then` variable. — Michael Berry, Jul 14 '20 at 17:15
Hey @Endrew .It's been quite a while since you posted this question. Any updates from your side? Did you try out the answer I provided ? — Abhinaba Chakraborty, Jul 22 '20 at 16:33

Abhinaba Chakraborty · Answer 1 · 2020-07-15T14:00:18.183

As @MichaelBerry mentioned, you are missing the block call.

It is clearly mentioned in the method documentation that:

Note that the writing process does not start until the returned Flux is subscribed to.

Below code worked for me:

public class MySpringBootApp {

  public static void main(String[] args) throws IOException {

    Path path = Paths.get("src/main/resources/sample.zip");
    WebClient client = WebClient.builder()
        .baseUrl("https://www.learningcontainer.com/wp-content/uploads/2020/05/sample-zip-file.zip")
        .build();
    Flux<DataBuffer> dataBufferFlux = client.get().retrieve().bodyToFlux(DataBuffer.class);
    DataBufferUtils.write(dataBufferFlux, path, StandardOpenOption.CREATE).block(); //Creates new file or overwrites exisiting file

  }


}

Downloading file using Spring Webclient, file is empty

1 Answers1