java如何清理DNS Cache

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原文地址：http://blog.csdn.net/teaey/article/details/17421927 专注请注明作者！

一、测试环境

OS：Windows7 x64

JDK：1.6.0_45

二、本人找到四种方式清理jvm的DNS缓存，大家可以根据自己的情况选用。

1. 在首次调用InetAddress.getByName()前，设置java.security.Security.setProperty("networkaddress.cache.ttl", "0");
2. 修改jre/lib/security/java.security 下的 networkaddress.cache.ttl 属性
3. jvm启动参数中设置-Dsun.net.inetaddr.ttl=0
4. 通过反射清理，如本文的clearCache方法

三、代码

package xiaofei;import java.lang.reflect.Field;import java.net.InetAddress;import java.net.UnknownHostException;import java.util.Map;/*** @author xiaofei.wxf* @date 13-12-18*/public class DNSCacheTest {    /**     * 1. 在首次调用InetAddress.getByName()前，设置java.security.Security.setProperty("networkaddress.cache.ttl", "0");     * 2. 修改jre/lib/security/java.security 下的 networkaddress.cache.ttl 属性     * 3. jvm启动参数中设置-Dsun.net.inetaddr.ttl=0     * 4. 调用clearCache方法清除     *     * @param args     * @throws UnknownHostException     */    public static void main(String[] args) throws UnknownHostException, NoSuchFieldException, IllegalAccessException {        java.security.Security.setProperty("networkaddress.cache.ttl", "0");        InetAddress addr1 = InetAddress.getByName("www.baidu.com");        System.out.println(addr1.getHostAddress());        //clearCache();        //在下一行设置断点.        //放在此处无效，因为类加载的时候就确定了这个值（应该在使用InetAddress.getByName之前设置）已经缓存了cache        //java.security.Security.setProperty("networkaddress.cache.ttl", "0");        InetAddress addr2 = InetAddress.getByName("www.baidu.com");        System.out.println(addr2.getHostAddress());        InetAddress addr3 = InetAddress.getByName("www.google.com");        System.out.println(addr3.getHostAddress());        InetAddress addr4 = InetAddress.getByName("www.google.com");        System.out.println(addr4.getHostAddress());        //clearCache();    }    public static void clearCache() throws NoSuchFieldException, IllegalAccessException {        //修改缓存数据开始        Class clazz = java.net.InetAddress.class;        final Field cacheField = clazz.getDeclaredField("addressCache");        cacheField.setAccessible(true);        final Object obj = cacheField.get(clazz);        Class cacheClazz = obj.getClass();        final Field cachePolicyField = cacheClazz.getDeclaredField("type");        final Field cacheMapField = cacheClazz.getDeclaredField("cache");        cachePolicyField.setAccessible(true);        cacheMapField.setAccessible(true);        final Map cacheMap = (Map)cacheMapField.get(obj);        System.out.println(cacheMap);        cacheMap.remove("www.baidu.com");    }}

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