Buy a copy at Leanpub!
The recommended price is $6 and the minimum price is $3. This includes PDF, Kindle, and iPad/iPhone formats and free updates as I fix any errors and update the book with new material.
You may want to look at the github repository for the book example code before purchasing this book to make sure that the material covered in my book will be of interest to you.
I will probably update the book in a few weeks after getting feedback from early readers. I am also still working on Clojure and JRuby wrapper for the Java code examples and as I update the code I will frequently push changes to the github repository for the example code.