使用反射机制修改JVM的DNS缓存

项目组遇到服务器无法解析localhost的问题，可把JVM的DNS缓存反射出来添加DNS解析

public static void addJVMDNSCache() throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
        Class clazz = java.net.InetAddress.class;
        final Field cacheField = clazz.getDeclaredField("addressCache");
        cacheField.setAccessible(true);
        final Object o = cacheField.get(clazz);
        Class clazz2 = o.getClass();
        final Field cacheMapField = clazz2.getDeclaredField("cache");
        cacheMapField.setAccessible(true);
        final Map cacheMap = (Map) cacheMapField.get(o);
        String ips[] = {"127.0.0.1"};
        AccessController.doPrivileged(new PrivilegedAction() {
            public Object run() {
                try {
                    Object entry = newCacheEntry("localhost", ips, InetAddressCachePolicy.FOREVER);
                    synchronized (o) {
                        //cacheMap.clear();
                        cacheMap.put("localhost", entry);
                    }
                } catch (Throwable te) {
                    throw new RuntimeException(te);
                }
                return null;
            }
        });
    }

    static Object newCacheEntry(String host, String[] ips, long expiration)
            throws UnknownHostException, ClassNotFoundException, NoSuchMethodException,
            IllegalAccessException, InvocationTargetException, InstantiationException {
        String className = "java.net.InetAddress$CacheEntry";
        Class clazz = Class.forName(className);

        // InetAddress.CacheEntry has only a constructor:
        // - for jdk 6, constructor signature is CacheEntry(Object address, long expiration)
        // - for jdk 7+, constructor signature is CacheEntry(InetAddress[] addresses, long expiration)
        // code in jdk 6:
        //   http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b27/java/net/InetAddress.java#InetAddress.CacheEntry
        // code in jdk 7:
        //   http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7-b147/java/net/InetAddress.java#InetAddress.CacheEntry
        // code in jdk 8:
        //   http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/8-b132/java/net/InetAddress.java#InetAddress.CacheEntry
        Constructor constructor = clazz.getDeclaredConstructors()[0];
        constructor.setAccessible(true);
        return constructor.newInstance(toInetAddressArray(host, ips), expiration);
    }

    static InetAddress[] toInetAddressArray(String host, String[] ips) throws UnknownHostException {
        InetAddress[] addresses = new InetAddress[ips.length];
        for (int i = 0; i < addresses.length; i++) {
            addresses[i] = InetAddress.getByAddress(host, IpParserUtil.ip2ByteArray(ips[i]));
        }

        return addresses;
    }