21.6 Java4560: session tracking using url rewriting

Table of contents

• Preface
  • Viewing tip
    • Figures
    • Listings
• General background information
• Discussion and sample code
  • The servlet program
    • Interesting code fragments
  • The JSP program
    • Interesting code fragments
• Run the programs
• Miscellaneous
• Complete program listings

Preface

This module is one in a collection of modules designed for teaching INEW 2338 Advanced Java (Web) at Austin Community College in Austin, TX. The purpose of this module is to explainsession tracking using URL rewriting, and to compare a servlet with a JSP to accomplish the same objective.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figures and Listings while you are reading about them.

Figures

• Figure 1 . The URL for hidden fields.
• Figure 2 . Servlet output screen.
• Figure 3 . HTML code created by servlet.

Listings

• Listing 1 . Beginning of the doGet method.
• Listing 2 . Get and save URL parameters named item.
• Listing 3 . Construct the new parameter string.
• Listing 4 . Concatenate current date and time to new parameter string.
• Listing 5 . Begin creation of the HTML page.
• Listing 6 . Construct the hyperlink.
• Listing 7 . Introductory text.
• Listing 8 . Display date and time history.
• Listing 9 . Display the current date and time.
• Listing 10 . Import necessary packages.
• Listing 11 . Get data from the old parameter string.
• Listing 12 . Construct a new parameter string.
• Listing 13 . Concatenate current date and time to the parameter string.
• Listing 14 . Create the hyperlink.
• Listing 15 . Display the list of dates.
• Listing 16 . The servlet named Java4560a.java
• Listing 17 . The JSP program named Java4560b.jsp.

General background information

A stateless protocol

You learned in earlier modules that the HTTP protocol is a relatively simple request/response protocol that does not retain historical information from oneclient request to the next. You also learned that historical information can be very important, and the maintenance of historical information is often referredto as "session tracking."

Session tracking

Because session tracking is very important for many web applications, an earlier module along with this and the next several modules will show you some of the ways that you can accomplish session tracking using servlets and JSP.

Session tracking using URL rewriting

There are several different ways to accomplish session tracking with a servlet. The earlier module explained session tracking using hidden fields. This module will illustrate how to accomplish session tracking using URL rewriting.

Limited persistence

You learned in the earlier module that the session tracking scheme using hidden fields is generally limited to one session consisting of multiple requests. You alsolearned that the scheme is probably not useful for large scale web commerce. However, it might be useful for an online game where the user makes a move andthen clicks a submit button. The computer needs to remember the entire history of the game, but needn't necessarily remember the history if theuser leaves the website by closing the browser page.