java 设置DNS缓存时间（成功时间和失败时间）代码

import java.lang.reflect.Field;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;
 
public class MyClass {
	public static void main(String[] args) throws Exception {
		Date d = new Date();
	    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
	    InetAddress.getByName("www.baidu.com");
	    try {
	        InetAddress.getByName("www.baiduxxx.com");
	    } catch (UnknownHostException e) {
	 
	    }
	 
	    System.out.println("current time:" + sdf.format(d));
	    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();//catchEntry
	    Field cf = cacheKlass.getDeclaredField("cache");
	    cf.setAccessible(true);//LinkedHashMap
	    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("addresses");
	        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);
	    }
	}
}