Java DNS cache viewer

Question

Is there a way to view/dump DNS cached used by java.net api?

Answer 1

Above answer does not work in Java 8 anymore. Here a slight adaption:

import java.lang.reflect.Field;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;

public class DNSCache {
    public static void main(String[] args) throws Exception {
        InetAddress.getByName("stackoverflow.com");
        InetAddress.getByName("www.google.com");
        InetAddress.getByName("www.yahoo.com");
        InetAddress.getByName("www.example.com");
        try {
            InetAddress.getByName("nowhere.example.com");
        } catch (UnknownHostException e) {

        }

        String addressCache = "addressCache";
        System.out.println(addressCache);
        printDNSCache(addressCache);
        String negativeCache = "negativeCache";
        System.out.println(negativeCache);
        printDNSCache(negativeCache);
    }

    private static void printDNSCache(String cacheName) throws Exception {
        Class klass = InetAddress.class;
        Field acf = klass.getDeclaredField(cacheName);
        acf.setAccessible(true);
        Object addressCache = acf.get(null);
        Class cacheKlass = addressCache.getClass();
        Field cf = cacheKlass.getDeclaredField("cache");
        cf.setAccessible(true);
        Map cache = (Map) cf.get(addressCache);
        for (Map.Entry hi : cache.entrySet()) {
            Object cacheEntry = hi.getValue();
            Class cacheEntryKlass = cacheEntry.getClass();
            Field expf = cacheEntryKlass.getDeclaredField("expiration");
            expf.setAccessible(true);
            long expires = (Long) expf.get(cacheEntry);

            Field af = cacheEntryKlass.getDeclaredField("addresses");
            af.setAccessible(true);
            InetAddress[] addresses = (InetAddress[]) af.get(cacheEntry);
            List ads = new ArrayList(addresses.length);
            for (InetAddress address : addresses) {
                ads.add(address.getHostAddress());
            }

            System.out.println(hi.getKey() + " expires in "
                    + Instant.now().until(Instant.ofEpochMilli(expires), ChronoUnit.SECONDS) + " seconds " + ads);
        }
    }
}