问题
I have an number of Java applications installed on an Ubuntu64 9.04 PC, and none of them can resolve domain names (there are multiple JRE's too - some of them are IBM products). If I put the domain name in the hosts file with it's associated IP address, then the Java apps work for those domains only. Every other non Java program - like ping, firefox, etc - work just fine with domain resolution. I've tried to disable DNS caching in the java.security file - for all of my JREs - but that didn't work either. I would appreciate some help in figuring this one out. Thanks!
UPDATE: I am sure there isn't a proxy server in my home or office. - I appreciate you guys helping me here. I REALLY want to use Linux instead of windows now that I'm doing Java development again.
jgreenwood@jeg-ubuntu64:~$ cat /etc/resolv.conf
# Generated by NetworkManager
domain hsd1.in.comcast.net.
search hsd1.in.comcast.net.
nameserver 192.168.0.1
jgreenwood@jeg-ubuntu64:~$ env | grep -i proxy
jgreenwood@jeg-ubuntu64:~$ dig google.com
; <<>> DiG 9.5.1-P2 <<>> google.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56845
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;google.com. IN A
;; ANSWER SECTION:
google.com. 58 IN A 74.125.53.100
google.com. 58 IN A 74.125.45.100
google.com. 58 IN A 74.125.67.100
;; Query time: 35 msec
;; SERVER: 192.168.0.1#53(192.168.0.1)
;; WHEN: Thu Oct 22 13:37:26 2009
;; MSG SIZE rcvd: 76
UPDATE: I wrote this java program in RAD:
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.io.PrintWriter;
import java.io.StringWriter;
public class DomainResolutionTest {
public static void main(String[] args) {
if (args.length == 0) args = new String[] { "www.google.com" };
try {
InetAddress ip = InetAddress.getByName(args[0]);
System.out.println(ip.toString());
}catch (UnknownHostException uhx) {
System.out.println("ERROR: " + uhx.getMessage() + "\n" + getStackTrace(uhx));
Throwable cause = uhx.getCause();
if (cause != null) System.out.println("CAUSE: " + cause.getMessage());
}
}
public static String getStackTrace(Throwable t)
{
StringWriter sw = new StringWriter();
PrintWriter pw = new PrintWriter(sw, true);
t.printStackTrace(pw);
pw.flush();
sw.flush();
return sw.toString();
}
}
The output is:
ERROR: www.google.com
java.net.UnknownHostException: www.google.com
at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:862)
at java.net.InetAddress.getAddressFromNameService(InetAddress.java:1213)
at java.net.InetAddress.getAllByName0(InetAddress.java:1166)
at java.net.InetAddress.getAllByName(InetAddress.java:1096)
at java.net.InetAddress.getAllByName(InetAddress.java:1032)
at java.net.InetAddress.getByName(InetAddress.java:982)
at DomainResolutionTest.main(DomainResolutionTest.java:12)
From the command line: (same result)
jgreenwood@jeg-ubuntu64:~$ javac DomainResolutionTest.java
jgreenwood@jeg-ubuntu64:~$ java DomainResolutionTest
ERROR: www.google.com
java.net.UnknownHostException: www.google.com
at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:849)
at java.net.InetAddress.getAddressFromNameService(InetAddress.java:1200)
at java.net.InetAddress.getAllByName0(InetAddress.java:1153)
at java.net.InetAddress.getAllByName(InetAddress.java:1083)
at java.net.InetAddress.getAllByName(InetAddress.java:1019)
at java.net.InetAddress.getByName(InetAddress.java:969)
at DomainResolutionTest.main(DomainResolutionTest.java:12)
jgreenwood@jeg-ubuntu64:~$ java -version
java version "1.6.0_16"
Java(TM) SE Runtime Environment (build 1.6.0_16-b01)
Java HotSpot(TM) Server VM (build 14.2-b01, mixed mode)
jgreenwood@jeg-ubuntu64:~$
回答1:
Once again, thanks to the guidance of the people here, I've found an answer. The Java program above works when I do the following:
java -Djava.net.preferIPv4Stack=true DomainResolutionTest
Details:
jgreenwood@jeg-ubuntu64:~$ java -Djava.net.preferIPv4Stack=true DomainResolutionTest
www.google.com/209.85.225.106
jgreenwood@jeg-ubuntu64:~$ java DomainResolutionTest ERROR: www.google.com
java.net.UnknownHostException: www.google.com
at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:849)
at java.net.InetAddress.getAddressFromNameService(InetAddress.java:1200)
at java.net.InetAddress.getAllByName0(InetAddress.java:1153)
at java.net.InetAddress.getAllByName(InetAddress.java:1083)
at java.net.InetAddress.getAllByName(InetAddress.java:1019)
at java.net.InetAddress.getByName(InetAddress.java:969)
at DomainResolutionTest.main(DomainResolutionTest.java:12)
It turns out that there is a bug in the IPv6 stack. There are a couple of posts that led me to this conclusion:
http://uclue.com/?xq=2127
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=477211
https://answers.launchpad.net/ubuntu/+question/23024
I sure hope I don't have to add the IPv4 crap in every time I run a Java app. The final solution may be in the second link - a missing package. We shall see.
Debian Bug report logs - #477211 ia32-sun-java6-bin: Needs to depend on lib32nss-mdns ... Cannot resolve domain names. Resolve fine on the rest of the system, have not tested with other JDK's. Installed from package and set with update-java-alternatives.
DNS works for everything else on my system. Running on Debian 2.6.23-AMD64. Have tried both Lenny packages and Sid packages. Works as expected with sun-java6-bin, fails with ia32-sun-java6-bin. Arg. ... If you hit java with strace you'll see that it is trying to use libnss_mdns4_minimal.so.2, which is available in the package lib32nss-mdns. You should add a dependency on that to fix the bug.
Same thing happens for sun-java6-bin - libnss-mdns is used here.
The package is indeed missing on my machine:
jgreenwood@jeg-ubuntu64:~$ dpkg -L lib32nss-mdns
Package `lib32nss-mdns' is not installed.
Use dpkg --info (= dpkg-deb --info) to examine archive files,
and dpkg --contents (= dpkg-deb --contents) to list their contents.
Either way, I hope this post helps someone else, because this was a major PITA to figure out.
回答2:
This solution (-Djava.net.preferIPv4Stack=true) also works when there is long runing lookupAllHostAddr.
来源：https://stackoverflow.com/questions/1608503/domain-name-resolution-not-working-in-java-applications-on-ubuntu64-9-04-machine