java实现清理DNS Cache的方法
本文实例讲述了java实现清理DNSCache的方法。分享给大家供大家参考。具体分析如下：
一、测试环境
OS：Windows7x64
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
packagexiaofei;
importjava.lang.reflect.Field;
importjava.net.InetAddress;
importjava.net.UnknownHostException;
importjava.util.Map;
/**
*@authorxiaofei.wxf
*@date13-12-18
*/
publicclassDNSCacheTest{
/**
*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
*
*@paramargs
*@throwsUnknownHostException
*/
publicstaticvoidmain(String[]args)throwsUnknownHostException,NoSuchFieldException,IllegalAccessException{
java.security.Security.setProperty("networkaddress.cache.ttl","0");
InetAddressaddr1=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");
InetAddressaddr2=InetAddress.getByName("www.baidu.com");
System.out.println(addr2.getHostAddress());
InetAddressaddr3=InetAddress.getByName("www.google.com");
System.out.println(addr3.getHostAddress());
InetAddressaddr4=InetAddress.getByName("www.google.com");
System.out.println(addr4.getHostAddress());
//clearCache();
}
publicstaticvoidclearCache()throwsNoSuchFieldException,IllegalAccessException{
//修改缓存数据开始
Classclazz=java.net.InetAddress.class;
finalFieldcacheField=clazz.getDeclaredField("addressCache");
cacheField.setAccessible(true);
finalObjectobj=cacheField.get(clazz);
ClasscacheClazz=obj.getClass();
finalFieldcachePolicyField=cacheClazz.getDeclaredField("type");
finalFieldcacheMapField=cacheClazz.getDeclaredField("cache");
cachePolicyField.setAccessible(true);
cacheMapField.setAccessible(true);
finalMapcacheMap=(Map)cacheMapField.get(obj);
System.out.println(cacheMap);
cacheMap.remove("www.baidu.com");
}
}
希望本文所述对大家的Java程序设计有所帮助。