// BookKeeperClient.commonInitialization
private synchronized void commonInitialization(
            DistributedLogConfiguration conf,
            String ledgersPath,
            EventLoopGroup eventLoopGroup,
            StatsLogger statsLogger, HashedWheelTimer requestTimer)
        throws IOException, InterruptedException {
// other code ...

Class<? extends DNSToSwitchMapping> dnsResolverCls;
        try {
             dnsResolverCls = conf.getEnsemblePlacementDnsResolverClass();
        } catch (ConfigurationException e) {
            LOG.error("Failed to load bk dns resolver : ", e);
            throw new IOException("Failed to load bk dns resolver : ", e);
        }
        final DNSToSwitchMapping dnsResolver =
                NetUtils.getDNSResolver(dnsResolverCls, conf.getBkDNSResolverOverrides());


// other code ...

}