jruby -S gem install json-jruby

json.rb

## install json-jruby library
# jruby -S gem install json-jruby
## create json.rb file which contains code below
## generate json.class file
# jrubyc json.rb
## run 
# java -cp .:/path/to/jruby-complete-1.7.4.jar json
## should see some output


require "rubygems"
require "json"

# de-serializing:
source_string = '{"sample": "Hello, world!"}'
puts JSON(source_string).inspect
# => {"sample"=>"Hello, world!"}

# serializing:
source_object = ["Just another Ruby Array", {"null value" => nil}]
puts JSON(source_object)
# => ["Just another Ruby Array",{"null value":null}]