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public class GrayScaleConvertWorkflowImpl implements GrayScaleConvertWorkflow {

    private S3ActivitiesClient s3ActivitiesClient = new S3ActivitiesClientImpl();
    private ImageActivitiesClient imageActivitiesClient = new ImageActivitiesClientImpl();
    private SNSActivitiesClient snsActivitiesClient = new SNSActivitiesClientImpl();

    @Override
    public void execute(File imageFile) {
        // 1.S3にアップロード
        Promise<S3Result> s3Result = s3ActivitiesClient.upload(imageFile);

        // 2.S3からダウンロード
        Promise<File> downloadTo = downloadFromS3(s3Result);

        // 3.画像コンバート
        Promise<ImageOperationResult> imageOpResult = convertToGrayScale(downloadTo);

        // 4.SNSで通知
        notifyOperationComplete(s3Result, imageOpResult);
    }

    @Asynchronous
    private Promise<File> downloadFromS3(Promise<S3Result> s3Result) {
        return s3ActivitiesClient.download(s3Result);
    }

    @Asynchronous
    private Promise<ImageOperationResult> convertToGrayScale(Promise<File> downloadTo) {
        return imageActivitiesClient.convertToGrayScale(downloadTo);
    }

    @Asynchronous
    private void notifyOperationComplete(Promise<S3Result> s3Result, Promise<ImageOperationResult> imageOpResult) {
        snsActivitiesClient.notifyOperationComplete(s3Result, imageOpResult);
    }
}