Downloading file using Spring Webclient, file is empty

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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?

spring-webclient spring-webflux spring java
1 Answers

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

  }


}
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