Get host name in java

Question

I am using jdk 8 with weblogic server 12 R2c. My application is public facing and i need to get the host name of the client. If the client host name is in the list of allowed host names which can access the application, then some special features are shown to them. Now my question is how to get the host name. I tried the below code and I am getting the following errors:

Errors:

1. java.net.UnknownHostException: 234:343:343f:d1d34:a34:c%c3:45263:ab3c, 449.6.087.678: invalid IPv6 address

2. java.net.UnknownHostException: 14.5.254.458, 65.15.5.15: unknown error.

   at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method) at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:928) at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1323) at java.net.InetAddress.getAllByName0(InetAddress.java:1276) at java.net.InetAddress.getAllByName(InetAddress.java:1192)

All the above IP address are sample dummy address which taken from my server log.

String ipAdr = request.getHeader("X-FORWARDED-FOR");
  if (ipAdr == null) {
    ipAdr = request.getRemoteAddr();
  }
  InetAddress addr = null;
  String host = null;
  if (ipAddress != null) {
    addr = InetAddress.getByName(ipAdr);
    host = addr.getHostName();
  }

It so happens the request may come from proxies server, in that case how to get the domain name. Tee above is in the filter code which is invoked for every request.

Answer 1

Here is a snippet of code that I am using to get the hostname of the machine, please refer to this answer as to why you should not get hostname using IP address.

public class App {
    private final static String HOSTNAME_COMMAND = "hostname";

    private static  String getHostName() throws IOException {
        Process process = Runtime.getRuntime().exec(HOSTNAME_COMMAND);
        BufferedReader inputStreamReader = new BufferedReader(new InputStreamReader(process.getInputStream()));
        BufferedReader errorStreamReader = new BufferedReader(new InputStreamReader(process.getErrorStream()));
        if (errorStreamReader.readLine() != null) {
            throw new RuntimeException(String.format("Failed to get the hostname, exception message: %s",
                    errorStreamReader.readLine()));
        }
        return inputStreamReader.readLine();
    }
}