This week's book giveaway is in the Performance forum. We're giving away four copies of The Java Performance Companion and have Charlie Hunt, Monica Beckwith, Poonam Parhar, & Bengt Rutisson on-line! See this thread for details.
A servlet pretends to be a web page, only it can be a whole new web page every time you hit it. If you fill out a form on a web page, that data can be sent to a servlet that generate new data for you. Like at MapQuest.com.