Getting the computer name in Java [duplicate]

I was wondering if there is a way to get the computer name in Java? I have seen several answers that feature java.net.InetAddress. However I was wondering if there is a way that does not use the network?

(As a side question, is the computer name only a network thing anyway, so therefore has to be done this way??)

The computer "name" is resolved from the IP address by the underlying DNS (Domain Name System) library of the OS. There's no universal concept of a computer name across OSes, but DNS is generally available. If the computer name hasn't been configured so DNS can resolve it, it isn't available.

import java.net.InetAddress;
import java.net.UnknownHostException;

String hostname = "Unknown";

try
{
    InetAddress addr;
    addr = InetAddress.getLocalHost();
    hostname = addr.getHostName();
}
catch (UnknownHostException ex)
{
    System.out.println("Hostname can not be resolved");
}

I agree with peterh's answer, so for those of you who like to copy and paste instead of 60 more seconds of Googling:

private String getComputerName()
{
    Map<String, String> env = System.getenv();
    if (env.containsKey("COMPUTERNAME"))
        return env.get("COMPUTERNAME");
    else if (env.containsKey("HOSTNAME"))
        return env.get("HOSTNAME");
    else
        return "Unknown Computer";
}

I have tested this in Windows 7 and it works. If peterh was right the else if should take care of Mac and Linux. Maybe someone can test this? You could also implement Brian Roach's answer inside the else if you wanted extra robustness.

I'm not so thrilled about the InetAddress.getLocalHost().getHostName() solution that you can find so many places on the Internet and indeed also here. That method will get you the hostname as seen from a network perspective. I can see two problems with this:

1. What if the host has multiple network interfaces ? The host may be known on the network by multiple names. The one returned by said method is indeterminate afaik.

2. What if the host is not connected to any network and has no network interfaces ?

All OS'es that I know of have the concept of naming a node/host irrespective of network. Sad that Java cannot return this in an easy way. This would be the environment variable COMPUTERNAME on all versions of Windows and the environment variable HOSTNAME on Unix/Linux/MacOS (or alternatively the output from host command hostname if the HOSTNAME environment variable is not available as is the case in old shells like Bourne and Korn).

I would write a method that would retrieve (depending on OS) those OS vars and only as a last resort use the InetAddress.getLocalHost().getHostName() method. But that's just me.

UPDATE (Unices)

As others have pointed out the HOSTNAME environment variable is typically not available to a Java application on Unix/Linux as it is not exported by default. Hence not a reliable method unless you are in control of the clients. This really sucks. Why isn't there a standard property with this information?

Alas, as far as I can see the only reliable way on Unix/Linux would be to make a JNI call to gethostname() or to use Runtime.exec() to capture the output from the hostname command. I don't particularly like any of these ideas but if anyone has a better idea I'm all ears. (update: I recently came across gethostname4j which seems to be the answer to my prayers).

Long read

I've created a long explanation in another answer on another post. In particular you may want to read it because it attempts to establish some terminology, gives concrete examples of when the InetAddress.getLocalHost().getHostName() solution will fail, and points to the only safe solution that I know of currently, namely gethostname4j.

It's sad that Java doesn't provide a method for obtaining the computername. Vote for JDK-8169296 if you are able to.