Launcher.java

import java.io.*;
import java.util.Map;

class StreamGobbler extends Thread {
    InputStream is;
    String type;

    StreamGobbler(InputStream is, String type) {
        this.is = is;
        this.type = type;
    }

    public void run() {
        try {
            InputStreamReader isr = new InputStreamReader( is );
            BufferedReader br = new BufferedReader( isr );
            String line = null;
            while ( !Thread.currentThread().isInterrupted() && ( line = br.readLine() ) != null ) {
                System.out.println( type + ">" + line );
            }
        }
        catch ( IOException ioe ) {
            ioe.printStackTrace();
        }
        System.out.println( "output thread ending" );

    }
}

public class ProcessLauncher {
    public static void main(String args[]) throws Exception {
        try {
            ProcessBuilder pb = new ProcessBuilder( "ruby", "spawner.rb" );
            pb.redirectErrorStream( true );
            Process proc = pb.start();

            StreamGobbler outputGobbler = new StreamGobbler(proc.getInputStream(), "OUTPUT");
            outputGobbler.start();

            int exitVal = proc.waitFor();
            System.out.println( "process returned:" + exitVal );

            outputGobbler.join();

            proc.destroy();
            System.out.println( "done" );
        }
        catch ( Throwable t ) {
            t.printStackTrace();
        }
    }
}

loop.rb

$stdout.sync = true
$stderr.sync = true

i = 0
while i < 10000
  $stdout.puts "Iteration #{i}"
  sleep 1
  i = i + 1
end


$stdout.puts "Bye from #{Process.pid}"

spawner.rb

require "tempfile"
require 'rbconfig'

class SpawnTest

  def self.spawn_process

    if os == :windows
      p1 = spawn('ruby', 'loop.rb', [:out, :err] => ['process.log', "w"],  :new_pgroup => true)
    else
      p1 = spawn('ruby', 'loop.rb', [:out, :err] => ['process.log', "w"],  :pgroup => true)
    end

    # Detach from the processes so they will keep running
    puts p1
    Process.detach(p1)
  end

  def self.os
    @os ||= (
    host_os = RbConfig::CONFIG['host_os']
    case host_os
      when /mswin|msys|mingw|cygwin|bccwin|wince|emc/
        :windows
      when /darwin|mac os/
        :macosx
      when /linux/
        :linux
      when /solaris|bsd/
        :unix
      else
        raise Error::WebDriverError, "unknown os: #{host_os.inspect}"
    end
    )
  end
end

if __FILE__ == $0
  SpawnTest.spawn_process
end