how to calculate size of S3 bucket if size is more than GB using java

Question

I am not able to calculate S3 bucket size if it is more than 300GB. I have used below code to calculate no of objects and bucket size. it is working for bucket less than 300gb size. I need to upload till 4TB and want to verify the no. of objects and size.

long totalSize = 0;
        int totalItems = 0; 
        List<S3Object> s3Obj = new ArrayList<S3Object>();
        ListObjectsResult result = null;
        do {
            if (result == null)
                result = s3JerseyClient.listObjects(bucketName);
            else
                result = s3JerseyClient.listMoreObjects(result);
            s3Obj.addAll(result.getObjects());            
             for (S3Object objectSummary : result.getObjects()) {
                totalSize += objectSummary.getSize();
                totalItems++;
            }
        } while (result.isTruncated());

if no of objects more than 600k above code is sometimes giving OOM error or it is running more than an hour