public String getMd5Digest() {
        return md5Digest;
    }
Returns the optional, but recommended, MD5 hash of the content of this
part. If specified, this value will be sent to Amazon S3 to verify the
data integrity when the data reaches Amazon S3.

@return The optional, but recommended, MD5 hash of the content of this
        part. If specified, this value will be sent to Amazon S3 to
        verify the data integrity when the data reaches Amazon S3.
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/model/UploadPartRequest.java