21.4 Java4550: session tracking using hidden fields

Table of contents

• Preface
  • Viewing tip
    • Figures
    • Listings
• General background information
• Discussion and sample code
  • The servlet program
    • Interesting code fragments
    • Tedious and error prone
  • 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 hidden fields, 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 servlet user interface at startup.
• Figure 2 . Browser display for Tom, Dick, and Harry.
• Figure 3 . Hidden fields in the servlet output.

Listings

• Listing 1 . Beginning of the servlet class.
• Listing 2 . Get and save the hidden values from the browser page.
• Listing 3 . Get and save user input data.
• Listing 4 . Begin constructing the HTML output data.
• Listing 5 . Begin the HTML code for an HTML form.
• Listing 6 . An input field and a submit button.
• Listing 7 . Beginning of the list of names.
• Listing 8 . Display the historical data and also save it on the browser.
• Listing 9 . Display most recent value and also store it on the browser.
• Listing 10 . Create basic web page structure.
• Listing 11 . A JSP scriptlet.
• Listing 12 . The body of the for loop.
• Listing 13 . Another scriptlet.
• Listing 14 . Another JSP expression tag.
• Listing 15 . Terminating scriptlet and HTML code.
• Listing 16 . The servlet program named Java4550a.java.
• Listing 17 . The JSP program named Java4550a.jsp.

General background information

A stateless protocol

The HTTP protocol is a relatively simple request/response protocol that does not retain historical information from one client request to the next. In otherwords, each request is a new start insofar as the HTTP server is concerned. (HTTP is sometimes referred to as a "stateless" protocol.) However, historical information can be very important. The maintenance ofhistorical information is often referred to as "session tracking."

Session tracking

Session tracking is very important for many web applications including web commerce and web games. Therefore, this and the next several modules will show you some of the ways thatyou can accomplish session tracking using servlets and JSP.

Web commerce

Perhaps the most common example of the need for session tracking is with a web commerce application involving a shopping cart. The customer (client) downloads various pages from a vendor catalog, selecting items, and placing themin a shopping cart. At some point, the customer decides either to purchase the items or abandon the shopping trip.

If the customer decides to purchase the items in the cart, the web application must have a record of all the items in the cart. Furthermore, thatrecord must be associated with that particular customer so that the sale can be consummated.