gistfile1.rbx

require 'java'
require 'poi-3.1-FINAL-20080629.jar'

class RubyOutputStream < java.io.OutputStream
  def initialize(io)
    super()
    @io = io
  end

  def write(b)
    if b.is_a?(Fixnum)
      if b < 0
        b = b + 256
      end
      @io.print(b.chr)
    else
      (0...b.length).each do |index|
        write(b[index])
      end
    end
  end

  def close
    @io.close
  end
end

io = File.open("test.xls", "w")
rio = RubyOutputStream.new(io)

wb = org.apache.poi.hssf.usermodel.HSSFWorkbook.new
wb.createSheet("First")
wb.write(rio)

rio.close