Use ListMultipartUploads with an AWS SDK or CLI

The following command lists all of the active multipart uploads for a bucket named my-bucket:

aws s3api list-multipart-uploads --bucket my-bucket

Output:

{
    "Uploads": [
        {
            "Initiator": {
                "DisplayName": "username",
                "ID": "arn:aws:iam::0123456789012:user/username"
            },
            "Initiated": "2015-06-02T18:01:30.000Z",
            "UploadId": "dfRtDYU0WWCCcH43C3WFbkRONycyCpTJJvxu2i5GYkZljF.Yxwh6XG7WfS2vC4to6HiV6Yjlx.cph0gtNBtJ8P3URCSbB7rjxI5iEwVDmgaXZOGgkk5nVTW16HOQ5l0R",
            "StorageClass": "STANDARD",
            "Key": "multipart/01",
            "Owner": {
                "DisplayName": "aws-account-name",
                "ID": "100719349fc3b6dcd7c820a124bf7aecd408092c3d7b51b38494939801fc248b"
            }
        }
    ],
    "CommonPrefixes": []
}

In progress multipart uploads incur storage costs in Amazon S3. Complete or abort an active multipart upload to remove its parts from your account.

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.ListMultipartUploadsRequest;
import software.amazon.awssdk.services.s3.model.ListMultipartUploadsResponse;
import software.amazon.awssdk.services.s3.model.MultipartUpload;
import software.amazon.awssdk.services.s3.model.S3Exception;
import java.util.List;

/**
 * Before running this Java V2 code example, set up your development
 * environment, including your credentials.
 *
 * For more information, see the following documentation topic:
 *
 * https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
 */

public class ListMultipartUploads {
    public static void main(String[] args) {
        final String usage = """

                Usage:
                    <bucketName>\s

                Where:
                    bucketName - The name of the Amazon S3 bucket where an in-progress multipart upload is occurring.
                """;

        if (args.length != 1) {
            System.out.println(usage);
            System.exit(1);
        }

        String bucketName = args[0];
        Region region = Region.US_EAST_1;
        S3Client s3 = S3Client.builder()
                .region(region)
                .build();
        listUploads(s3, bucketName);
        s3.close();
    }

    /**
     * Lists the multipart uploads currently in progress in the specified Amazon S3 bucket.
     *
     * @param s3 the S3Client object used to interact with Amazon S3
     * @param bucketName the name of the Amazon S3 bucket to list the multipart uploads for
     */
    public static void listUploads(S3Client s3, String bucketName) {
        try {
            ListMultipartUploadsRequest listMultipartUploadsRequest = ListMultipartUploadsRequest.builder()
                    .bucket(bucketName)
                    .build();

            ListMultipartUploadsResponse response = s3.listMultipartUploads(listMultipartUploadsRequest);
            List<MultipartUpload> uploads = response.uploads();
            for (MultipartUpload upload : uploads) {
                System.out.println("Upload in progress: Key = \"" + upload.key() + "\", id = " + upload.uploadId());
            }

        } catch (S3Exception e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }
}