Using inetaddress to find host names

Question

I am currently writing a java program in which I need to capture the ip address of the client machine in which the browser is running. I know I can do this, but how can I find the host name associated with this ip address. If I run the code below, I receive the host name on some machines, but others I get the ip address returned.
I only want to allow people to use my site that have a valid host name. Any suggestions?
Code:
import java.net.*;
public class iplookup {
public static void main(String[] args) {
     try {
          System.setProperty("sun.net.spi.nameservice.provider.1", "dns,sun");
          String test1 = args [0];
          InetAddress local = InetAddress.getByName(args[0]);
          System.out.println("Host Address = " + local.getHostAddress());
          System.out.println("Host Name = " + local.getHostName());
          System.out.println("Host Canonical Name = " + local.getCanonicalHostName());
          System.out.println("args = " + test1);
          String test2 = local.getHostAddress().toString();
          if (test1 == test2) {
               System.out.println("bad address");
     catch(Exception e) {
          System.out.println("bad address");
          e.printStackTrace();
}

Answer 1

Thanks for the help! I am trying to use the conditional statement to
check if the ipaddress has an associated host name. I am finding that if the ip address does not have a hostname, the method getHostName returns the ipaddress. I am using this logic to filter out ipaddress that do not have a host name associated with it. I understand that I will receive an exception if an ipaddress is not a valid ipaddress. But I also want to make sure that the ip has an associated hostname.
Is my assumption correct?