Java: no timeout on DNS resolution

Breaking news! I just discovered (well. actually yesterday) that it’s not possible to set a timeout on DNS resolution in Java, which relies on the underlying OS. This is NOT good when you have any shape or form of SLA or QOS, you basically potentially throwing it out of the window!

I suggest you do something about it, this is the code I pushed on msnos (see here code and test), basically it uses a Threadpool and a Future to make the magic happen:

import org.apache.http.conn.DnsResolver;
public class DnsResolverWithTimeout implements DnsResolver {

    public InetAddress[] resolve(final String host) throws UnknownHostException {

        Future<InetAddress[]> result = executor.submit(new Callable<InetAddress[]>() {
            public InetAddress[] call() throws Exception {
                return systemResolver.resolve(host);

        try {
            return result.get(timeoutInMillis, TimeUnit.MILLISECONDS);
        } catch (InterruptedException e) {
            log.warn("Unexpected interrupton while resolving host "+host, e);
        } catch (ExecutionException e) {
            log.warn("Unexpected execution exception", e.getCause());
        } catch (TimeoutException e) {
            log.warn("Timeout of {} millis elapsed resolving host {}", timeoutInMillis, host);

        throw new UnknownHostException(host + ": DNS timeout");

Of course you can make sure your OS is behaving, but you may not have such luxury 🙂


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