How do I get the Hostname in Java?

[cpjust]

I'm trying to find the best way of getting the system's Hostname in Java.
I haven't found a function specifically for it, which is strange, I would have expected that would be common enough to be in there somewhere.

I tried this not so portable way to get it on UNIX:

System.out.println( "HOSTNAME = " + System.getenv( "HOSTNAME" ) );

But for some reason it prints "HOSTNAME = null".

I also tried this way which sort of works, except on my Linux desktop where it returns the vmnet8 adapter name instead of the real hostname:

	static String GetMachineName() throws SocketException
	{
		String name = null;
		Enumeration<NetworkInterface> enet = NetworkInterface.getNetworkInterfaces();

		while ( enet.hasMoreElements() && (name == null) )
		{
			NetworkInterface net = enet.nextElement();

			if ( net.isLoopback() )
				continue;

			Enumeration<InetAddress> eaddr = net.getInetAddresses();

			while ( eaddr.hasMoreElements() )
			{
				InetAddress inet = eaddr.nextElement();

				if ( inet.getCanonicalHostName().equalsIgnoreCase( inet.getHostAddress() ) == false )
				{
					name = inet.getCanonicalHostName();
					break;
				}
			}
		}

		return name;
	}

Any ideas of how to reliably get the hostname in Java?

[cpjust]

Here's another not so portable way that seems to work, but I'm not a big fan of non-portable solutions:

Runtime run = Runtime.getRuntime();
Process proc = run.exec( "hostname" );
BufferedInputStream in = new BufferedInputStream( proc.getInputStream() );
byte [] b = new byte[256];
System.out.println( new String( b ) );

BTW, does the 'hostname' program exist on every UNIX system or is it sometimes not installed on some systems?

[Dino]

Running hostname on my Mac:

dinos-computer:MyApplets dino hostname
dinos-computer.local
dinos-computer:MyApplets dino $

[sorrofix]

This seems to run fine on my Mac.

class PrintHostname
{
  public static void main(String args[]) throws java.net.UnknownHostException
  {
    java.net.InetAddress addr = java.net.InetAddress.getLocalHost();
    String hostname = addr.getHostName();
    System.out.println("Hostname of system = " + hostname);
  }
}

results:

kitty:~ $ javac PrintHostname.java
kitty:~ $ java PrintHostname
Hostname of system = kitty
kitty:~ $

>BTW, does the 'hostname' program exist on every UNIX system
To my knowledge, yes.

[cpjust]

Yes, that seems to run fine on my system too, but does that mean it will work on all systems?
I'm worried that it might not always return the correct name on machines with multiple Network Interfaces...

I'm wondering what Java means by "LocalHost"? To me that sounds like the loopback address, but it can't be, since it's returning the real hostname rather than "localhost".

[stevesmithx]

Yes, that seems to run fine on my system too, but does that mean it will work on all systems?
I'm worried that it might not always return the correct name on machines with multiple Network Interfaces...

I'm wondering what Java means by "LocalHost"? To me that sounds like the loopback address, but it can't be, since it's returning the real hostname rather than "localhost".

I think localhost means the loopback address 127.0.0.1 which gets resolved to the hostname which when invoked by getHostName() method.

[CornedBee]

How do you define the "real" hostname? What about my machine that is in two networks with two different names, both being equal? What's its "real" hostname?

Your endeavor is doomed.

[sorrofix]

Wait, are we talking about the same thing here? From my understanding, by 'hostname' cpjust was referring to the name of the machine, not the DNS name that other machines use to refer to the machine. The Single Unix Specification only allows one hostname (or rather, POSIX) and I'm pretty sure all the Unix-derivatives are the same.

For example:
http://opengroup.org/onlinepubs/0079...thostname.html

The Unix utility 'hostname' when run without any arguments actually calls gethostname().

As for the code snippet I posted, I can't vouch for the correctness of that. I based it off some other code I found online and really don't know if that's the 'correct' way to do it.

[CornedBee]

So either execute hostname and capture the output (if POSIX defines it, it's as portable as you're going to get) or JNI-wrap gethostname(). Or find a POSIX system interface Java library - Googling for "java posix" yields a lot of stuff.
http://basepath.com/aup/jtux/

[cpjust]

You know, I may be pursuing an untamed ornithoid without cause (Star Trek humor), so maybe I'll just use this:

java.net.InetAddress.getLocalHost().getHostName();

and if I actually run into any problems with that code, then I'll worry about using some other method.