re-implementing "native" gem APIs (sample)

serial_port_jruby.rb

# Emulates the SerialPort class that uses a native C extension.
class SerialPort < IO

  load "java/jna.jar"
  load "java/purejavacomm-0.0.21.jar"
  java_import 'purejavacomm.CommPortIdentifier'

  def initialize(port)
    # do what SerialPort C does on Windows (for compat): 0 -> 'COM1'
    port = "COM#{port + 1}" if port.is_a?(Integer) && windows?
    port_id = CommPortIdentifier.getPortIdentifier(port.to_s)
    @serial_port = port_id.open 'MyApp', 1500 # timeout milliseconds
  end

  def write(buffer)
    @serial_port.getOutputStream.write buffer.to_java_bytes
  end

  def close; @serial_port.close end

  # ... etc.

end if defined? JRUBY_VERSION

require 'serialport.so' unless defined? JRUBY_VERSION