title: A strange UnknownHostException
body: <p>In a web project .<Br/>
  I see the log:</p>
  
  <pre><code>hadoop.hbase.zookeeper.ZKConfig - java.net.UnknownHostException: example.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)
  </code></pre>
  
  <p>but when I <strong>ping example.com</strong>, it's ok, I also <strong>telnet example.com 2181</strong> successfully!
  I found the <a href="https://stackoverflow.com/questions/1608503/domain-name-resolution-not-working-in-java-applications-on-ubuntu64-9-04-machine">similar question</a>
  so I run the DomainResolutionTest in my Server  <strong>java DomainResolutionTest example.com</strong>
  <br>
  but it's ok !</p>
  
  <p>env:</p>
  
  <pre><code>java -version
  </code></pre>
  
  <p>java version "1.6.0_25" <br>
  Java(TM) SE Runtime Environment (build 1.6.0_25-b06)<br>
  Java HotSpot(TM) 64-Bit Server VM (build 20.0-b11, mixed mode)<br></p>
  
  <p><code>os:Red Hat Enterprise Linux Server release 5.7</code></p>
  
  <p><strong>I am curious why is Inet6AddressImpl,I think it  may be Inet4AddressImpl</strong></p>
  
  <p>How to solve it? 
  <br>What's the cause ?</p>