Can InetAddress represent host names that can't be resolved?

Question

I parse various data sources with network information in them.

I have been using java.net.InetAddress to represent and parse hosts. It works fine being initialized with IP.

I have to parse a new source now. It contains hostnames instead of IP's. InetAddress.getByName() throws UnknownHostException if a hostname argument can't be resolved to an IP. Host IP isn't absolutely neccessary for my goal. Dropping the data just because of DNS failure is unacceptable for me.

I'd like to have an IP address if it is obtainable or a hostname otherwise.

How do I prevent resolve of given hostnames? Is there another class that is more suited for my needs?

Answer 1

I guess that this is not possible, because the core function of InetAddress is to handle IP-Addresses:

This class represents an Internet Protocol (IP) address.

An IP address is either a 32-bit or 128-bit unsigned number used by IP, a lower-level protocol on which protocols like UDP and TCP are built. The IP address architecture is defined by RFC 790: Assigned Numbers, RFC 1918: Address Allocation for Private Internets, RFC 2365: Administratively Scoped IP Multicast, and RFC 2373: IP Version 6 Addressing Architecture. An instance of an InetAddress consists of an IP address and possibly its corresponding host name (depending on whether it is constructed with a host name or whether it has already done reverse host name resolution).

You have no possibility to construct an InetAddress object without an IP-address.

For you purpose you need to define a Hostname.class, which holds the hostname and maybe additional data. This class should/can handle all the domainname internationalization via IDN, if you are using Java 6. There are separate IDN libraries available if you are on Java 5.

A separate Hostname.class can also define guards or constructors, which assure only valid hostnames according to the relevant RFCs.

Answer 2

The method InetAddress.getByAddress(String host, byte[] addr) does not perform a query to the DNS and allows you to create an InetAddress having arbitrary hostname and IP address, possibly the IPv4 unspecified address (0.0.0.0).

Try creating the InetAddress with getByName, if it throws you can create it by using getByAddress. Note that you will need to check the IP addresses are valid before actually using them.

---

Example code:

  public static void main(String arg[])
    throws  UnknownHostException
  {
    InetAddress a;
    byte[] unspec = new byte[4];
    unspec[0]=0;
    unspec[1]=0;
    unspec[2]=0;
    unspec[3]=0;
    try
    {
      a = InetAddress.getByName(arg[0]);
    }
    catch(UnknownHostException e)
    {
      a = InetAddress.getByAddress(arg[0],unspec);
    }
    System.out.println(a);
  }

Answer 3

How about writing a new class? It would only need to be able to store a String and an InetAddress.