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9.3 A Servlet Showing Per Client Access Counts

207

Core Approach

Plan ahead: pass URLs that refer to your own site through 

response.encodeURL

 or 

response.encodeRedirectURL

, 

regardless of whether your servlet is using session tracking.

9.3 A Servlet Showing Per Client 

Access Counts

Listing 9.1 presents a simple servlet that shows basic information about the

client's session. When the client connects, the servlet uses 

request.getSes 

sion(true)

 to either retrieve the existing session or, if there was no session,

to create a new one. The servlet then looks for an attribute of type 

Integer

called 

accessCount

. If it cannot find such an attribute, it uses 0 as the num 

ber of previous accesses. This value is then incremented and associated with

the session by 

putValue

. Finally, the servlet prints a small HTML table

showing information about the session. Figures 9 1 and 9 2 show the servlet

on the initial visit and after the page was reloaded several times. 

Listing 9.1 ShowSession.java 

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

import java.net.*;

import java.util.*;

/** Simple example of session tracking. See the shopping

 *  cart example for a more detailed one.

 */

public class ShowSession extends HttpServlet {

  public void doGet(HttpServletRequest request,

                    HttpServletResponse response)

      throws ServletException, IOException {

    response.setContentType("text/html");

    PrintWriter out = response.getWriter();

    String title = "Session Tracking Example";

    HttpSession session = request.getSession(true);

    String heading;

    // Use getAttribute instead of getValue in version 2.2.

    Integer accessCount =

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