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Track wireless sessions with J2ME/MIDP

Learn three ways to maintain client state information in mobile commerce applications

By Michael Juntao Yuan and Ju Long, JavaWorld.com, 04/26/02

Client state information proves vital for e-commerce applications that employ user authentication and transactions. In those applications, the server must individually respond to each user according to her previous actions. For example, when a user places an item into a shopping cart, the server must remember and associate that item with that particular user. When the same user selects Checkout later, the server must respond with a list of the merchandise she previously selected.

However, the most widely used Internet e-commerce protocol, HTTP, is stateless. Each HTTP connection is independent and knows nothing about other connections. Standard HTTP connections do not remember client state information. Most developers solve this problem by requiring the client to embed some unique session identification information (usually a session ID string) in each HTTP connection. E-commerce Web servers can then organize individual HTTP connections into sessions according to the session identification. It usually works like so:

1. When a new session's first connection is made, the server generates a new session ID and sends it back to the client
2. The client stores that session ID and attaches it to every subsequent HTTP connection so the server knows all connections belong to the same session

That technique requires cooperation between the client and server software. The client and server must exchange session identification information with a previously agreed upon format. The industry has developed two de facto standards for exchanging such session information.

One approach transmits small pieces of text, called cookies, through HTTP connection headers. The other approach attaches a session ID string to the end of each request URL, a technique also known as URL rewriting.

Most Web browsers and desktop HTTP applications support both session-tracking methods. However, the HTTP session support in wireless Java platforms is far from smooth. In the main Java platform designed for cell phones and low-powered PDAs—the Mobile Information Device Profile (MIDP), a Java 2 Platform, Micro Edition (J2ME)-based technology—the HttpConnection object supports neither cookie nor URL rewriting out of the box. Considering the importance of session tracking in e-commerce applications, if we want J2ME/MIDP to be a serious mobile commerce platform, we must equip it with session-aware HTTP connections.

In this article, we discuss how to implement session tracking in MIDP applications with both cookies and URL rewriting. We will also discuss a new way to track sessions by enveloping session information in XML documents. The XML method is unique to wireless applications. (Note: We assume you have basic knowledge of MIDP programming. If you need a refresher, please refer to Resources.)

As we mentioned earlier, session tracking requires a joint effort from both the client and the server. In this article, we give examples in the context of Java application servers, but you can easily apply the same techniques to other servers.

 

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