这是一个打印正负DNS地址缓存的脚本。
import java.lang.reflect.Field;import java.net.InetAddress;import java.net.UnknownHostException;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<InetAddress> 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<String, Object> cache = (Map<String, Object>) cf.get(addressCache); for (Map.Entry<String, Object> 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("address"); af.setAccessible(true); InetAddress[] addresses = (InetAddress[]) af.get(cacheEntry); List<String> ads = new ArrayList<String>(addresses.length); for (InetAddress address : addresses) { ads.add(address.getHostAddress()); } System.out.println(hi.getKey() + " "+new Date(expires) +" " +ads); } }}
