Java DNS缓存查看器
Java DNS缓存查看器
提问于 2009-12-03 04:03:15
有没有办法查看/转储java.net应用程序接口使用的DNS缓存？
回答 3
Stack Overflow用户
回答已采纳
发布于 2009-12-09 13:06:30
下面是一个打印正负DNS地址缓存的脚本。
import java.lang.reflect.Field;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;
public class DNSCache {
public static void main(String[] args) throws Exception {
InetAddress.getByName("stackoverflow.com");
InetAddress.getByName("www.google.com");
InetAddress.getByName("www.yahoo.com");
InetAddress.getByName("www.example.com");
try {
InetAddress.getByName("nowhere.example.com");
} catch (UnknownHostException e) {
}
String addressCache = "addressCache";
System.out.println(addressCache);
printDNSCache(addressCache);
String negativeCache = "negativeCache";
System.out.println(negativeCache);
printDNSCache(negativeCache);
}
private static void printDNSCache(String cacheName) throws Exception {
Class<InetAddress> klass = InetAddress.class;
Field acf = klass.getDeclaredField(cacheName);
acf.setAccessible(true);
Object addressCache = acf.get(null);
Class cacheKlass = addressCache.getClass();
Field cf = cacheKlass.getDeclaredField("cache");
cf.setAccessible(true);
Map<String, Object> cache = (Map<String, Object>) cf.get(addressCache);
for (Map.Entry<String, Object> hi : cache.entrySet()) {
Object cacheEntry = hi.getValue();
Class cacheEntryKlass = cacheEntry.getClass();
Field expf = cacheEntryKlass.getDeclaredField("expiration");
expf.setAccessible(true);
long expires = (Long) expf.get(cacheEntry);
Field af = cacheEntryKlass.getDeclaredField("address");
af.setAccessible(true);
InetAddress[] addresses = (InetAddress[]) af.get(cacheEntry);
List<String> ads = new ArrayList<String>(addresses.length);
for (InetAddress address : addresses) {
ads.add(address.getHostAddress());
}
System.out.println(hi.getKey() + " "+new Date(expires) +" " +ads);
}
}
}Stack Overflow用户
发布于 2017-07-18 02:27:02
上面的答案在Java 8中不再有效。下面是一个小小的调整：
import java.lang.reflect.Field;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;
public class DNSCache {
public static void main(String[] args) throws Exception {
InetAddress.getByName("stackoverflow.com");
InetAddress.getByName("www.google.com");
InetAddress.getByName("www.yahoo.com");
InetAddress.getByName("www.example.com");
try {
InetAddress.getByName("nowhere.example.com");
} catch (UnknownHostException e) {
}
String addressCache = "addressCache";
System.out.println(addressCache);
printDNSCache(addressCache);
String negativeCache = "negativeCache";
System.out.println(negativeCache);
printDNSCache(negativeCache);
}
private static void printDNSCache(String cacheName) throws Exception {
Class<InetAddress> klass = InetAddress.class;
Field acf = klass.getDeclaredField(cacheName);
acf.setAccessible(true);
Object addressCache = acf.get(null);
Class cacheKlass = addressCache.getClass();
Field cf = cacheKlass.getDeclaredField("cache");
cf.setAccessible(true);
Map<String, Object> cache = (Map<String, Object>) cf.get(addressCache);
for (Map.Entry<String, Object> hi : cache.entrySet()) {
Object cacheEntry = hi.getValue();
Class cacheEntryKlass = cacheEntry.getClass();
Field expf = cacheEntryKlass.getDeclaredField("expiration");
expf.setAccessible(true);
long expires = (Long) expf.get(cacheEntry);
Field af = cacheEntryKlass.getDeclaredField("addresses");
af.setAccessible(true);
InetAddress[] addresses = (InetAddress[]) af.get(cacheEntry);
List<String> ads = new ArrayList<String>(addresses.length);
for (InetAddress address : addresses) {
ads.add(address.getHostAddress());
}
System.out.println(hi.getKey() + " expires in "
+ Instant.now().until(Instant.ofEpochMilli(expires), ChronoUnit.SECONDS) + " seconds " + ads);
}
}
}Stack Overflow用户
发布于 2020-10-21 17:27:57
上面的答案不适用于Java 11。在Java 11中，可以使用' cache‘实例变量检索正和负缓存条目。以下是新的改编：
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.lang.reflect.Field;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
public class DnsCacheFetcher {
static long startTimeinNano = System.nanoTime();
public static void main(String[] args) throws Exception {
System.out.println("SecurityManager: " + System.getSecurityManager());
InetAddress.getByName("stackoverflow.com");
InetAddress.getByName("www.google.com");
InetAddress.getByName("www.yahoo.com");
InetAddress.getByName("www.ankit.com");
try {
InetAddress.getByName("nowhere.example.com");
} catch (UnknownHostException e) {
System.out.println("Unknown host: " + e);
}
String addressCache = "cache";
System.out.println(">>>>" + addressCache);
printDNSCache(addressCache);
/*
* String negativeCache = "negativeCache"; System.out.println(">>>>" +
* negativeCache); printDNSCache(negativeCache);
*/
}
private static void printDNSCache(String cacheName) throws Exception {
Class<InetAddress> klass = InetAddress.class;
Field[] fields = klass.getDeclaredFields();
/*
* for (Field field : fields) { System.out.println(field.getName()); }
*/
Field acf = klass.getDeclaredField(cacheName);
acf.setAccessible(true);
Object addressCache = acf.get(null);
Class cacheKlass = addressCache.getClass();
Map<String, Object> cache = (Map<String, Object>) acf.get(addressCache);
for (Map.Entry<String, Object> hi : cache.entrySet()) {
/* System.out.println("Fetching cache for: " + hi.getKey()); */
Object cacheEntry = hi.getValue();
Class cacheEntryKlass = cacheEntry.getClass();
Field expf = cacheEntryKlass.getDeclaredField("expiryTime");
expf.setAccessible(true);
long expires = (Long) expf.get(cacheEntry);
Field af = cacheEntryKlass.getDeclaredField("inetAddresses");
af.setAccessible(true);
InetAddress[] addresses = (InetAddress[]) af.get(cacheEntry);
List<String> ads = null;
if (addresses != null) {
ads = new ArrayList<String>(addresses.length);
for (InetAddress address : addresses) {
ads.add(address.getHostAddress());
}
}
/*
* System.out.println(hi.getKey() + " expires in " +
* (Instant.now().until(Instant.ofEpochMilli(expires), ChronoUnit.SECONDS)) +
* " seconds. inetAddresses: " + ads);
*/
/*
* System.nanoTime() + 1000_000_000L * cachePolicy : this how java 11 set
* expiryTime
*/
System.out.println(hi.getKey() + " expires in approx " + (expires - startTimeinNano) / 1000_000_000L
+ " seconds. inetAddresses: " + ads);
}
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原文链接：
https://stackoverflow.com/questions/1835421
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