Using the Java 7 WatchService API with JRuby 1.7.9

watcher.rb

require 'java'

class Watcher
  java_import java.nio.file.FileSystems
  java_import java.nio.file.StandardWatchEventKinds

  IGNORE_PATHS = [
    /\/vendor/,
    /\/public/,
    /\/tmp/,
    /\.git/,
    /\.bundle/,
    /\.sass-cache/,
    /\/log/
  ]

  def initialize(path)
    @fs = FileSystems.get_default
    @watcher = @fs.new_watch_service
    register_path(path)
    start
  end

  def start
    puts "Start"
    begin
      key = @watcher.take()
      loop do
        key.poll_events.each do |ev|
          case ev.kind()
          when StandardWatchEventKinds::ENTRY_CREATE
            puts "Created: #{ev.context}"
          when StandardWatchEventKinds::ENTRY_DELETE
            puts "Deleted: #{ev.context}"
          when StandardWatchEventKinds::ENTRY_MODIFY
            puts "Modified #{ev.context}"
          end
        end
      end
    rescue => e
      puts "Error: #{e}"
    end
  end

  private

  def ignore_path?(path)
    IGNORE_PATHS.any? { |x| path =~ x }
  end

  def register_path(path, recursive = true)
    return if ignore_path?(path)

    puts "Register: #{path}"

    dir = @fs.get_path(path)
    dir.register(@watcher, StandardWatchEventKinds::ENTRY_CREATE,
                           StandardWatchEventKinds::ENTRY_DELETE,
                           StandardWatchEventKinds::ENTRY_MODIFY)


    return unless recursive

    Dir[File.join(path,'*','/')].each do |sub|
      register_path(sub)
    end
  end
end

w = Watcher.new('/Users/jmcnevin/Source/fp2')
w.start