This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
Your servlet ServletUser doesnt implement doGet method, and hence when you enter the URL to servlet in browser addressbar and hit enter, you get this error.
Implement doGet in your servlet and the error will go away.