InetAddress.getByName fails behind proxy

问题

I'm trying to resolve a host name to its' corresponding IP.

My environment is a mac in a corporate network behind a proxy server, which is configured with a .pac file via the system preferences (automatic proxy configuration). So far everything is working fine and I can access resources inside and outside my corporate network.

Resolving hosts within my network works perfectly fine: InetAddress.getByName("host.local");

But when I use external host names, I get a UnknownHostException: InetAddress.getByName("google.com");

produces

Exception in thread "main" java.net.UnknownHostException: google.com
    at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
    at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:850)
    at java.net.InetAddress.getAddressFromNameService(InetAddress.java:1201)
    at java.net.InetAddress.getAllByName0(InetAddress.java:1154)
    at java.net.InetAddress.getAllByName(InetAddress.java:1084)
    at java.net.InetAddress.getAllByName(InetAddress.java:1020)
    at java.net.InetAddress.getByName(InetAddress.java:970)
    at Test.main(Test.java:67)

(I'm a little bit surprised about Inet6AddressImpl here)

As far as I understand is InetAddress.getByName using the native mechanisms to resolve host names. So I don't think that the error is caused by a missing proxy configuration within the java jvm.

But what else can it be, if everything else is working fine?

Some (maybe) useful additional information:

I'm using a MacBook, ifconfig shows the interfaces lo0, gif0, stf0, en0, fw0, en1 -> connected to the network, with ipv4 address.
nslookup google.com on the console returns ** server can't find google.com: NXDOMAIN
The same code on a windows machine within the network produced the same Exception

Any ideas about the cause of this error? Or are there other ways to resolve host names in java?

回答1:

Your corporate DNS server prevents you from resolving any Interent domain ( they probably do not want people browsing non-corporate context ).

This is supported by the fact that your nslookup query fails.

If you don't have a vote on your corporate policy, and your development machine has to stay on your company premises, there is nothing that you can do.

回答2:

As mentioned in this post, you can set custom DNS via a Sun-JVM only setting. I had this same resolution issue, but was able to ask the proxy explicitly for the lookup by settting it as the DNS server also. YMMV

System.setProperty("sun.net.spi.nameservice.nameservers", "<my-proxy-ip>");
System.setProperty("sun.net.spi.nameservice.provider.1", "dns,sun");

回答3:

I know that this question has been updated, but because it is the top listed result in Google, I wanted to add this useful piece of information which might trip people up.

When using this method, remember the following.

http://www.google.com -- DOES NOT WORK
google.com -- WORKS!

来源：https://stackoverflow.com/questions/6911590/inetaddress-getbyname-fails-behind-proxy

标签

java

proxy

hostname

resolve