Finding Large Prime Numbers

• The ability of servlets to maintain persistent state. In this case, the servlet starts a low-priority thread to calculate prime numbers, and returns a page showing initial results. Whenever the client asks for an update, it returns the new results. It also maintains a set of the 30 most recently calculated results, to return immediately if a client asks for something already computed.
• The ability of servlets to manipulate HTTP response headers. In this case, it sends Refresh headers if the prime calculations are not yet complete, along with a page showing the intermediate results.