DnsWithTimeout.java

package /* YOUR PROJECT PACKAGE */.utils;

import android.support.annotation.*;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

import okhttp3.Dns;
import rx.Observable;
import rx.schedulers.Schedulers;

/** implements DNS lookup/resolve client with timeout feature. */
public class DnsEx implements Dns {
    /** Empty instance used as indicator of TIMEOUT exception. */
    private static final List<InetAddress> TIMEOUT = Collections.emptyList();
    /** timeout in millis. */
    private final long mTimeoutDns;

    /** Hidden constructor. */
    private DnsEx(final long dnsTimeoutMillis) {
        mTimeoutDns = dnsTimeoutMillis;
    }

    /** Create a new instance with specific timeout. */
    @NonNull
    public static DnsEx timeout(final int time, @NonNull final TimeUnit units) {
        final long millis = units.toMillis(time);

        return new DnsEx(millis);
    }

    /** {@inheritDoc} */
    @Override
    public List<InetAddress> lookup(@NonNull final String address) throws UnknownHostException {
        final List<InetAddress> results = Observable.fromCallable(
                new Callable<List<InetAddress>>() {
                    @Override
                    public List<InetAddress> call() throws Exception {
                        return Dns.SYSTEM.lookup(address);
                    }
                })
                .subscribeOn(Schedulers.computation())
                .timeout(mTimeoutDns, TimeUnit.MILLISECONDS, Observable.just(TIMEOUT))
                .toBlocking()
                .firstOrDefault(TIMEOUT);

        if (TIMEOUT == results) {
            final String message = "Cannot resolve '" + address + "' in " + mTimeoutDns + " ms.";

            // wrap Timeout exception into UnknownHostException
            final UnknownHostException unknown = new UnknownHostException(address);
            unknown.initCause(new TimeoutException(message));

            throw unknown;
        }

        return results;
    }
}

usage:

        return new OkHttpClient.Builder()
                .connectTimeout(TIMEOUT_CONNECT, TimeUnit.SECONDS)
                .readTimeout(TIMEOUT_READ, TimeUnit.SECONDS)
                .writeTimeout(TIMEOUT_WRITE, TimeUnit.SECONDS)
                .dns(DnsEx.timeout(TIMEOUT_DNS, TimeUnit.SECONDS))
                .addInterceptor(logging)
                .build();