Use CreateMultipartUpload with an AWS SDK

Create a multipart upload in a directory bucket.

import com.example.s3.util.S3DirectoryBucketUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.CreateMultipartUploadRequest;
import software.amazon.awssdk.services.s3.model.CreateMultipartUploadResponse;
import software.amazon.awssdk.services.s3.model.S3Exception;

import static com.example.s3.util.S3DirectoryBucketUtils.createDirectoryBucket;
import static com.example.s3.util.S3DirectoryBucketUtils.createS3Client;
import static com.example.s3.util.S3DirectoryBucketUtils.deleteDirectoryBucket;

    /**
     * This method creates a multipart upload request that generates a unique upload
     * ID used to track
     * all the upload parts.
     *
     * @param s3Client   The S3 client used to interact with S3
     * @param bucketName The name of the directory bucket
     * @param objectKey  The key (name) of the object to be uploaded
     * @return The upload ID used to track the multipart upload
     */
    public static String createDirectoryBucketMultipartUpload(S3Client s3Client, String bucketName, String objectKey) {
        logger.info("Creating multipart upload for object: {} in bucket: {}", objectKey, bucketName);

        try {
            // Create a CreateMultipartUploadRequest
            CreateMultipartUploadRequest createMultipartUploadRequest = CreateMultipartUploadRequest.builder()
                    .bucket(bucketName)
                    .key(objectKey)
                    .build();

            // Initiate the multipart upload
            CreateMultipartUploadResponse response = s3Client.createMultipartUpload(createMultipartUploadRequest);
            String uploadId = response.uploadId();
            logger.info("Multipart upload initiated. Upload ID: {}", uploadId);
            return uploadId;

        } catch (S3Exception e) {
            logger.error("Failed to create multipart upload: {} - Error code: {}", e.awsErrorDetails().errorMessage(),
                    e.awsErrorDetails().errorCode(), e);
            throw e;
        }
    }