Sessions in Servlets

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The following examples show the newer session tracking API in use within Servlets.

The first time a user runs the "Barman" servlet, it sets up a session for him and prompts for his name. On subsequent visits, it addresses him by name straight away, and also keeps a tally of how many times he's visited.

The "Landlord" servlet does the same as the Barman, but in addition it maintains a static vector of sessions so that it can (and does ;-) ) report on everyone in the bar and how much they've had to drink.

Note - "Barman" keeps the users apart, which is typically what you would do with a shopping cart ... "Landlord" provides a management information service too ....

::::::::::::::
Barman.java
::::::::::::::
import java.io.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

/**
* Simple Session Tracking
*/

public class Barman extends HttpServlet {

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

HttpSession session = request.getSession(true);
Integer count = (Integer)session.getAttribute("mycounter");
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<body bgcolor=\"white\">");

if (count == null) {
  count = new Integer(0);
  out.print("<h1>Welcome. Please enter your name</h1>");
  out.print("<form action=/nan/servlet/Barman>");
  out.print("<input name=whoyouare>");
  out.print("</form>");
} else {
  String wanted = request.getParameter("whoyouare");
  if (wanted != null) {
   session.setAttribute("who",wanted);
  } else {
   wanted = (String)session.getAttribute("who");
  }
  count = new Integer(count.intValue() + 1);
  out.print("<h1>Welcome back "+wanted+"</h1>");
  out.println("This is your visit no. "+count+"<BR>");
}
session.setAttribute("mycounter",count);
        out.println("</body>");
        out.println("</html>");
    }
}

::::::::::::::
Landlord.java
::::::::::::::
import java.io.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

/**
* Simple Session Tracking
* Also reports on all users
*/

public class Landlord extends HttpServlet {

public static Vector People;

public void init(ServletConfig cc) throws ServletException {
super.init(cc);
People = new Vector();
}

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

HttpSession session = request.getSession(true);
Integer count = (Integer)session.getAttribute("mycounter");
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<body bgcolor=\"white\">");

if (count == null) {
  count = new Integer(0);
  out.print("<h1>Welcome. Please enter your name</h1>");
  out.print("<form action=/nan/servlet/Landlord>");
  out.print("<input name=whoyouare>");
  out.print("</form>");
  People.addElement(session);
} else {
  String wanted = request.getParameter("whoyouare");
  if (wanted != null) {
   session.setAttribute("who",wanted);
  } else {
   wanted = (String)session.getAttribute("who");
  }
  count = new Integer(count.intValue() + 1);
  out.print("<h1>Welcome back "+wanted+"</h1>");
  out.println("This is your visit no. "+count+"<BR>");
  out.println("<BR><H2>Those here present ...</h2>");

  for (int i=0; i<People.size();i++) {
   HttpSession present = (HttpSession)(People.elementAt(i));
   String ere = (String)present.getAttribute("who");
   out.print(ere+ " is here and has drunk ");
   int ii = ((Integer)present.getAttribute("mycounter")).intValue();
   out.print("" + ii + " previously<BR>");
   }
}
session.setAttribute("mycounter",count);
        out.println("</body>");
        out.println("</html>");
    }
}

See also Servlets in more detail

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