Java Smart Ticket Demo Application Scrutinized

For the Java component model J2EE, Sun has published guidelines which show how to use their technology effectively to create enterprise applications. These guidelines are illustrated in the two example enterprise application blueprints Pet Store and Smart Ticket. Since our group is working on a wireless project, we investigated the Smart Ticket demo application. This paper describes our experiences until we had the application running on real Java cell phones and shows weaknesses and bugs in the demo application. 1 Wireless Enterprise Applications The Smart Ticket is a sample application which illustrates the guidelines to build J2EE applications. The sample application allows users to buy movie tickets through a mobile device such as a cell phone. Users can select a movie, choose a movie theater, a show-time, select one or more seats and then purchase the tickets. Figure 1 shows a seating plan where three seats in the first row have been selected. The demo application is available from Sun on the Web [1, 2]. Fig. 1. Seating Plan In our group, we are working on a similar project. The idea is to purchase tickets for parking lots via cell phones. Our server can either be accessed through a Java cell phone (as in the Smart Ticket sample application) or through a SMS 2 Dominik Gruntz and René Müller or USSD gateway. The reservation may also be forwarded to the parking ticket machine which prints a ticket [3]. As we wanted to apply the J2EE infrastructure appropriately, we carefully studied the Smart Ticket blueprint application (version 1.1.1) and installed it on several application servers. It was very instructive to see how the J2EE design patterns are applied in practice. While studying the code of the Smart Ticket application we also found (and fixed) some bugs which was very instructive too. The goal of this paper is to share our experiences and to point out potential pitfalls programmers may face with enterprise applications. However we want to emphasize that we consider the blueprint initiative (and the Smart Ticket application) as very valuable, although the critical remarks may outweigh the positive ones in this paper. We hope, that our comments help to improve the application and that the readers can also benefit from the problems discussed. We also installed the midlet part of the Smart Ticket application on real Java cell phones (Siemens SL45i, Nokia 3410, and Motorola Accompli 008). The application did not run on those three cell phones right away. Regardless of these experiences, we worked around the problems these cell phones still have. The application is now running reasonably on the Siemens SL45i and on the Accompli 008, but memory restrictions of the cell phones are still the most limiting factor. The paper is organized as follows. In chapter 2 we describe the architecture of the Smart Ticket application, and in chapters 3 and 4 we describe the server part in more detail and discuss the encountered problems. Chapter 5 describes the problems we met when we installed the client part on real cell phones and the workarounds we used. The last chapter contains our concluding remarks. 2 Architecture of the Smart Ticket Demo Application The Smart Ticket application is designed as a multi-tier architecture (see Figure 2) and follows the MVC pattern. The business logic is implemented in EJBs on top of the database. The EJBs are accessed from a servlet which accepts requests from MIDP clients over HTTP. The MIDP client is responsible for the data presentation. The client tier consists of a MIDP/CLDC application providing the user interface. The data is presented in forms, lists or on canvas objects and the application state is controlled with a state machine. Personal preferences (like user name, password) and all messages of a particular locale setting (internationalization support) are stored in record stores on the cell phone. The web tier handles the HTTP POST requests from the midlet. A simple message format is used to specify the commands. The web tier is also responsible for the session management. Sessions are controlled with a session listener. 1 Btw, we can completely agree with a quote by Lars Bak (Sun microsystems). At his presentation at JavaOne 2002 he emphasized that ”we work on things that you can throw against the wall.” Java Smart Ticket Demo Application Scrutinized 3