How to implement clearing DNS Cache in java

The example in this article describes the method of cleaning DNS Cache in Java. Share it with everyone for your reference. The specific analysis is as follows:

1. Test environment

OS: Windows7 x64

JDK: 1.6.0_45

2. I found four ways to clear the DNS cache of jvm. You can choose according to your own situation.

1. Before calling InetAddress.getByName() for the first time, set java.security.Security.setProperty("networkaddress.cache.ttl", "0");
2. Modify the networkaddress.cache.ttl property under jre/lib/security/java.security
3. Set -Dsun.net.inetaddr.ttl=0 in the jvm startup parameters
4. Cleaning through reflection, such as the clearCache method in this article

3. Code
Copy the code as follows: 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. Before calling InetAddress.getByName() for the first time, set java.security.Security.setProperty("networkaddress.cache.ttl", "0");
* 2. Modify the networkaddress.cache.ttl property under jre/lib/security/java.security
* 3. Set -Dsun.net.inetaddr.ttl=0 in jvm startup parameters
* 4. Call clearCache method to clear
*
* @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();
//Set a breakpoint on the next line.
//It is invalid to put it here, because this value is determined when the class is loaded (it should be set before using InetAddress.getByName) and has been cached.
//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 {
//Start modifying cache data
Classclazz = 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");
}
}

I hope this article will be helpful to everyone’s Java programming.