Also known as FrontController, FrontServlet is a DesignPattern where all requests for a particular WebApplication are directed to the same servlet before being handled, sometimes by other servlets, jsp action handlers or whatever.

Sometimes implemented as having all the webapp servlets inherit from a FrontController servlet.

The idea is to have a single point where you can modify the behavior of the entire webapp. For example, security related checks are much more robust if put there instead of being put in every jsp page.

See JavaServlet.