require 'rubygems'
require 'fileutils'
require 'zip/zip'
require 'zip/zipfilesystem'
require 'rubygems/command_manager'

# ...
      def gem_bundler(args)
        Gem.platforms = [Gem::Platform::RUBY,
            Gem::Platform.new('universal-java')]
        Gem.configuration = Gem::ConfigFile.new(args.unshift('bundle'))
        puts "=> Bundling gems"
        begin
          Gem::CommandManager.instance.run(Gem.configuration.args)
        rescue Gem::SystemExitException => e
          exit e.exit_code unless e.exit_code == 0
        end
        if !args.include?('--update') and File.exists?(app.gems_jar) and
            File.stat(app.gems_jar).mtime > File.stat(app.gemfile).mtime
          return
        end
        gem_files = Dir["#{app.gems_dir}/**/**"]
        FileUtils.rm app.gems_jar, :force => true # blow away the old jar
        puts "=> Installing gems"
        Zip::ZipFile.open(app.gems_jar, 'w') do |jar|
          gem_files.reject {|f| f == app.gems_jar}.each do |file|
            jar.add(file.sub("#{app.gems_dir}/",''), file)
          end
        end
      end

# ...