java code for Servlet : session filter

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

public class SessionFilter implements Filter {

private FilterConfig config;

/** Creates new SessionFilter */
public SessionFilter() {
}

public void init(FilterConfig filterConfig) throws ServletException {

System.out.println("Instance created of " + getClass().getName());
this.config = filterConfig;
}

public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws java.io.IOException, ServletException {

HttpSession session = ((HttpServletRequest) request).getSession();
ServletContext context = config.getServletContext();
/*
* use the ServletContext.log method to log filter messages
*/
context.log("doFilter called in: " + config.getFilterName() + " on "
+ (new java.util.Date()));

// log the session ID
context.log("session ID: " + session.getId());

// Find out whether the logged-in session attribute is set
String logged = (String) session.getAttribute("logged-in");
if (logged == null)
session.setAttribute("logged-in", "no");

//log a message about the log-in status
context.log("log-in status: "
+ (String) session.getAttribute("logged-in"));
context.log("");
chain.doFilter(request, response);
}

public void destroy() {
/*
* called before the Filter instance is removed from service by the web
* container
*/
}
}