ServletContextListener example

Before going into the details of ServletContextListener we should understand what is ServletContext. ServletContext is a interface which helps us to communicate with the servlet container. There is only one ServletContext for the entire web application and the components of the web application can share it. The information in the ServletContext will be common to all the components. Remember that each servlet will have its own ServletConfig. The ServetContext is created by the container when the web application is deployed and after that only the context is available to each servlet in the web application.

ServletContextListener is a interface which contains two methods:

public void contextInitialized(ServletContextEvent event)
public void contextDestroyed(ServletContextEvent event)

When we implement any interface then we have to implement its all methods. This listener will help a application to start and shutdown the events.

How the ServletContextListener is useful:

1. ServletContextListener is notified when the context is initialized.

a). ServletContextListener gets the context init parameters from the ServletContext.

b). It stores the database connection as an attribute, so that the other components in the web application can access it.

2. It will be notified when the context is destroyed. It closes the database connection.

The code of the program is given below:

import javax.servlet.*;
import javax.servlet.http.*;

public class MyServletContextListener implements ServletContextListener{
public void contextInitialized(ServletContextEvent event)
{
ServletContext sc = event.getServletContext();
String whatType = sc.getInitParameter("typeSelected");
Furniture f = new Furniture(whatType);
sc.setAttribute("furniture", f);
}
public void contextDestroyed(ServletContextEvent event)
{

}
}

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class ListenerTester extends javax.servlet.http.HttpServlet
implements javax.servlet.Servlet {
public ListenerTester() {
super();
}

public void doGet(HttpServletRequest request, }
HttpServletResponse response) throws
ServletException, IOException {
// TODO Auto-generated method stub
response.setContentType("text/html");
PrintWriter pw = response.getWriter();
pw.println("context attributes set by the listener <br>");
Furniture f = (Furniture)getServletContext().getAttribute("furniture");
pw.println("The furniture you have selected is :" + f.getTypeSelected());
}

public void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}

The output of the program is given below:

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