JavaServer Pages, 3rd Edition

Servlet Lifecycle

The web container manages all aspects of the servlet’s lifecycle. It creates an instance of the servlet class when needed, passes requests to the instance for processing, and eventually removes the instance. For an HttpServlet, the container calls the following methods at the appropriate times in the servlet lifecycle:

public void init( ) throws ServletExecption

Called once, before the first request is delivered. This method can be used to initialize the servlet’s state, for instance by reading initialization parameters defined in the web application deployment descriptor and saving the values in instance variables to be used during request processing.

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException

Called repeatedly to let the servlet process a GET request. The request parameter provides detailed information about the request, and the servlet uses the response parameter to generate the response.

public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException

Called repeatedly to let the servlet process a POST request.

public void destroy( )

Called once, before the servlet is taken out of service. This method can be used to save to permanent storage data accumulated during the servlet’s lifetime and to remove references to objects held by the servlet.

Besides the doGet( ) and doPost( ) methods, there are methods corresponding to the other HTTP methods: ...