public final TransferManagerBuilder withS3Client(AmazonS3 s3Client) {
        setS3Client(s3Client);
        return this;
    }
Sets the low level client used to make the service calls to Amazon S3. If no
client is specified, a default client will be created using {@link DefaultAwsRegionProviderChain}
and {@link DefaultAWSCredentialsProviderChain}.

@param s3Client Client implementation to use
@return This object for method chaining.
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/transfer/TransferManagerBuilder.java