public final HttpClientBuilder setProxySelector(final ProxySelector proxySelector) {
        this.proxySelector = proxySelector;
        return this;
    }
Sets the {@link ProxySelector} that will be used to select the proxies
to be used for establishing HTTP connections. If a non-null proxy selector is set,
it will take precedence over the proxy settings configured in the client.

@param proxySelector the {@link ProxySelector} to be used, or null to use
                     the default system proxy selector.
@return this instance.
httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/HttpClientBuilder.java