AWS SDK for Java v2

static void upload(S3Client s3, String bucket, String key, byte[] body) {
    s3.putObject(
            PutObjectRequest.builder()
                    .bucket(bucket)
                    .key(key)
                    .contentType("text/plain")
                    .build(),
            RequestBody.fromBytes(body));
}

static byte[] download(S3Client s3, String bucket, String key) {
    return s3.getObjectAsBytes(
                    GetObjectRequest.builder().bucket(bucket).key(key).build())
            .asByteArray();
}

static List<String> listPrefix(S3Client s3, String bucket, String prefix) {
    List<String> keys = new ArrayList<>();
    s3.listObjectsV2Paginator(
                    ListObjectsV2Request.builder().bucket(bucket).prefix(prefix).build())
            .contents()
            .forEach((S3Object object) -> keys.add(object.key()));
    return keys;
}

static URL presign(String bucket, String key) {
    try (S3Presigner presigner = S3Presigner.builder()
            .endpointOverride(URI.create(System.getenv("AWS_ENDPOINT_URL")))
            .region(Region.of(System.getenv("AWS_REGION")))
            .credentialsProvider(StaticCredentialsProvider.create(
                    AwsBasicCredentials.create(
                            System.getenv("AWS_ACCESS_KEY_ID"),
                            System.getenv("AWS_SECRET_ACCESS_KEY"))))
            // The presigner needs path style told to it separately from the client.
            .serviceConfiguration(software.amazon.awssdk.services.s3.S3Configuration.builder()
                    .pathStyleAccessEnabled(true)
                    .build())
            .build()) {

        return presigner.presignGetObject(GetObjectPresignRequest.builder()
                        .signatureDuration(Duration.ofHours(1)) // 7 days is the maximum
                        .getObjectRequest(GetObjectRequest.builder()
                                .bucket(bucket)
                                .key(key)
                                .build())
                        .build())
                .url();
    }
}

static void delete(S3Client s3, String bucket, String key) {
    s3.deleteObject(DeleteObjectRequest.builder().bucket(bucket).key(key).build());
}