def java_opts
    if $win
      enable_server = $config['jvm.server'] == 'true'
    else
      enable_server = $config['jvm.server'] == 'true' || `java -d32 -version 2>&1` =~ /Cannot run Java in 32 bit mode/ || $? != 0
      arch = enable_server ? '-d64' : '-d32'
    end
    vm_opts   = enable_server ? ['-server', '-Xmx2G', '-XX:MaxPermSize=256M'] : ['-client', '-Xms128M', '-Xmx256M', '-XX:MaxPermSize=128M']
    user_opts = "#{ENV['JAVA_OPTS']} #{$config['jvm.opts']}".split.compact
    [arch, vm_opts, user_opts, @java_opts,'-cp', classpath, %{-Djava.library.path="#{libpath}"}]
  end