Java Servlet Programming

The Servlet API

Now that you have a basic understanding of HTTP, we can move on and talk about the Servlet API that you’ll be using to create HTTP servlets, or any kind of servlets, for that matter. Servlets use classes and interfaces from two packages: javax.servlet and javax.servlet.http . The javax.servlet package contains classes to support generic, protocol-independent servlets. These classes are extended by the classes in the javax.servlet.http package to add HTTP-specific functionality. The top-level package name is javax instead of the familiar java, to indicate that the Servlet API is a standard extension.

Every servlet must implement the javax.servlet.Servlet interface. Most servlets implement it by extending one of two special classes: javax. servlet.GenericServlet or javax.servlet.http.HttpServlet . A protocol-independent servlet should subclass GenericServlet, while an HTTP servlet should subclass HttpServlet, which is itself a subclass of GenericServlet with added HTTP-specific functionality.

Unlike a regular Java program, and just like an applet, a servlet does not have a main() method. Instead, certain methods of a servlet are invoked by the server in the process of handling requests. Each time the server dispatches a request to a servlet, it invokes the servlet’s service() method.

A generic servlet should override its service() method to handle requests as appropriate for the servlet. The service() method accepts two parameters: a request object and ...