java 设置指定域名的ip解析

Test.java

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Map;

public class Test {

	public static void main(String[] args) {
		try {
			Field field = InetAddress.class.getDeclaredField("addressCache");
			field.setAccessible(true);
			Object addressCache = field.get(null);

			// 获取Map
			Field cacheMapField = addressCache.getClass().getDeclaredField("cache");
			cacheMapField.setAccessible(true);
			Map cacheMap = (Map) cacheMapField.get(addressCache);

			// 获取CacheEntry(内部类) Map 的 Value
			Class<?> cls = Class.forName("java.net.InetAddress$CacheEntry");
			Constructor<?> constructor = cls.getDeclaredConstructor(InetAddress[].class, long.class);
			constructor.setAccessible(true);
			InetAddress[] ipAddr = new InetAddress[1];
			ipAddr[0] = getInetAddr("127.0.0.1");
			Object value = constructor.newInstance(ipAddr, -1);

			// 设置host(永不过期)
			synchronized (addressCache) {
				cacheMap.put("www.baidu.com", value);
			}

			// 测试
			InetAddress addresses = InetAddress.getByName("www.baidu.com");
			System.out.println(addresses.getHostAddress());
			Thread.sleep(40000);
			addresses = InetAddress.getByName("www.baidu.com");
			System.out.println(addresses.getHostAddress());
			
			// 还原可见性
			constructor.setAccessible(false);
			field.setAccessible(false);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	static InetAddress getInetAddr(String ip) throws UnknownHostException {
		String[] ipStr = ip.split("\\.");
		byte[] ipBuf = new byte[4];
		for (int i = 0; i < 4; i++) {
			ipBuf[i] = (byte) (Integer.parseInt(ipStr[i]) & 0xff);
		}
		return InetAddress.getByAddress(ipBuf);
	}
}