Core Servlets and JavaServer Pages™

7.3. Persistent Servlet State and Auto-Reloading Pages

Here is an example that lets you ask for a list of some large, randomly chosen prime numbers. This computation may take some time for very large numbers (e.g., 150 digits), so the servlet immediately returns initial results but then keeps calculating, using a low-priority thread so that it won't degrade Web server performance. If the calculations are not complete, the servlet instructs the browser to ask for a new page in a few seconds by sending it a Refresh header.

In addition to illustrating the value of HTTP response headers, this example shows two other valuable servlet capabilities. First, it shows that the same servlet can handle multiple simultaneous connections, each with its own ...