/******************************************************************** * * HelloSession.java * * Represents three pages: A, B, and C -- the form has a button * to go to each of the three. * Creates a "session" object on the first client interaction. * Uses the session to keep track of sequence of visits over the * whole session. * ********************************************************************/ import java.io.*; import java.text.*; import java.util.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloSession extends HttpServlet { // One instance of the Tracker class is what is stored in the // session. The Tracker keeps track of the number of interactions // and an array of the sequence of pages visited. // Java note: you can declare nested utility classes like this private class Tracker { private int count; private Vector series; // Vector is a dynamic array that stores Objects // Vector responds to: size(), addElement(), and elementAt() public Tracker() { count = 0; series = new Vector(); } public void upCount() { count++; } public int getCount() { return(count); } public void add(Object object) { series.addElement(object); } public void printSeries(PrintWriter out) { for (int i=0; i"); out.println(""); String title = "Hello Session"; out.println("" + title + ""); out.println(""); out.println(""); out.println("

" + title + "

"); // See if there is a session already // If not, create the session and put a new tracker in it // If there is an existing session, get the tracker out of it Tracker tracker = null; HttpSession session = request.getSession(false); if (session == null) { out.println("Hello there! I haven't seen you before have I? Creating a session."); session = request.getSession(true); tracker = new Tracker(); session.putValue("tracker", tracker); } else { tracker = (Tracker) session.getValue("tracker"); } // At this point, a session and tracker object are established // Increment the number of visits and print the greeting tracker.upCount(); String time; if (tracker.getCount() == 1) time = " time "; else time = " times "; out.println("Dang if we haven't served you " + tracker.getCount() + time + "this session"); // Standard technique to look at which button was pressed to // return the right page (the page string is for the visit tracking) String page; if (request.getParameter("gotob") != null) { doB(out); page = "b"; } else if (request.getParameter("gotoc") != null) { doC(out); page = "c"; } else { doA(out); // the page of last resort page = "a"; } tracker.add(page); // Just to show off the session state we are keeping, // echo the series of visits for this whole session out.println("

Order of visits so far..."); tracker.printSeries(out); // Print the form with the A B C buttons last doForm(out); out.println(""); out.println(""); } // Separated out utilities for the HTML generation... public void doForm(PrintWriter out) { out.println("

"); } public void doA(PrintWriter out) { out.println("

The A page rules

"); out.println("

This dress exacerbates the genetic betrayal that is my legacy."); } public void doB(PrintWriter out) { out.println("

The B page rules

"); out.println("

Clattu barrada nickto."); } public void doC(PrintWriter out) { out.println("

The C page rules

"); out.println("

Picture this -- I'm hiding naked in a refrigerator."); } }