public Builder setProxy(final String hostName, final int port) {
            if (hostName == null || hostName.length() == 0) {
                throw(new IllegalArgumentException(
                        "Proxy host name cannot be null or empty"));
            }
            if (port <= 0) {
                throw(new IllegalArgumentException(
                        "Proxy port must be > 0"));
            }
            config.proxyHost = hostName;
            config.proxyPort = port;
            return this;
        }