This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
It's not the server that is idempotent or not. It's the HTTP method that gets this quality. All methods other than POST are idempotent. Meaning, you can call them again and again without side effects. For POST, you need to write code to take care of this or else you'll find that your database contains loads of duplicate entries (caused by someone hitting submit again and again)! That is what is my understanding from HFSJ. Hope that helps. Amit