Today, Budi walks us through a refresher and brief overview of server JSP programming. Today's portion covers Servlet technologies, including servlets and Tomcat. This excerpt comes from chapter one of JavaServer Faces Programming, by Budi Kurniawan (McGraw-Hill/Osborne, ISBN 0-07-222983-7, 2004).
The init method is called the first time the servlet is invoked. It is called exactly once to indicate to the servlet that the servlet is being placed into service. You override this method to write initialization code that needs to be executed only once, such as initializing values, loading database drivers, and so on.
The following is the methodís signature:
public void init(ServletConfig config) throws ServletException
The service Method
The service method is called by the servlet container each time the servlet is invoked. For each incoming HTTP request, the servlet container creates a request object (that implements javax.servlet.ServletRequest or javax.servlet.http.HttpServletRequest) and a response object (that implements javax.servlet.ServletResponse or javax.servlet.http.HttpServletResponse) and passes both objects to the servletís service method. The request object encapsulates information parsed from the HTTP request that the servlet can use, such as the request URI, request headers and cookies, and request parameters. The servlet uses the response object to send responses to the Web client.
The service method has the following signature:
public void service(ServletRequest request, ServletResponse response)throws ServletException, java.io.IOException
TIP: If youíre interested in knowing how a servlet container creates request and response objects, or how it works in general, read How Tomcat Works, available from www.brainysoftware.com.
The destroy Method
The servlet container calls the destroy method before removing a servlet instance from service. This normally happens when the servlet container is shut down or the servlet container needs some free memory. You use this method to clean up any resources (such as memory, file handles, and threads) that are being held and make sure that any persistent state is synchronized with the servletís current state in memory. The following is the destroy methodís signature:
public void destroy()
Remember: This is part one of the first chapter of JavaServer Faces Programming, by Budi Kurniawan (McGraw-Hill/Osborne, ISBN 0-07-222983). Stay tuned for part 2 of "Overviews of Java Web Technologies," where we learn about JSP, JavaBeans, and Model 2. Buy this book!