ArcUser Online

ArcIMS Java Client Supplies Mapping to Phones
Continued...

The middleware is implemented as a Java 2, Enterprise Edition (J2EE) servlet running on a Java servlet-enabled Web server. The client uses J2ME's Mobile Information Device Profile (MIDP), and the server uses one of J2EE's application programming interfaces (APIs). Because both client and server are written in Java, a single implementation of MultiProtocol was created that provides code for handling messages and protocol for both client and server. This makes development of additional services easier and faster—a very important feature of MultiProtocol. Because the client cannot send anything the server does not understand and vice versa, it also effectively reduces possible error states.

A J2ME Map Client for ArcIMS

Mobile Map Explorer (MEx) is a simple map browser for small Java-enabled devices, such as cell phones, that have an Internet connection. Although it has limited functionality caused primarily by the application size limit of 64 KB (typically), this J2ME map client includes all important functionality of a common map browser. The user can choose any map server, move around the displayed map, zoom in and out, identify objects on the map, and show map tips for important map features. MEx can search for a location using the names of two intersecting streets. The displayed map can also be stored as a bookmark so the user can easily return and continue browsing. If the device has a color display with high resolution, the J2ME map client represents a very good alternative to common ArcIMS map browsers based on HTML.

MIDP 2.0 and the Location API for J2ME-Coming Soon

Although current technologies allow the creation of a viable mobile map browser application, development in the area of wireless devices is rapidly advancing. Currently there are two new technologies worth mentioning—Mobile Information Device Profile (MIDP) 2.0 and the Location API for J2ME.

MIDP 2.0 is a new profile for mobile devices that has already been implemented in several new devices (e.g., Nokia 6600, Motorola A760). [A profile is a J2ME API for programming electronic devices. For more information on J2ME, see the accompanying article, "What Is J2ME?"] This profile includes new functionality such as user interface enhancements, the ability to receive incoming network messages, and support for encrypted communication via HTTPS. Visit java.sun.com/products/midp/ for more information on MIDP 2.0.

The Location API for J2ME was developed as an optional package for J2ME. Development on this API was led by Nokia. A few of the many companies participating in this specification include Motorola, Cisco, Sun, IBM, Esri, Symbian, and Vodafone. The Location API should enable implementing devices to get information about the current location of the device. It does not specify which method is used to determine the location. For example, the implementation can use satellite-based methods such as GPS, cellular network-based methods, and short-range positioning methods such as Bluetooth Local Positioning. The implementation may also combine the methods in various ways to get optimal results. More information about this specification is available at jcp.org/en/jsr/detail?id=179. The authors believe both technologies will be incorporated into most wireless devices and will make them more attractive as clients of spatially enabled information systems.

Summary

The broad availability of J2ME-enabled wireless devices and the fact that people usually carry wireless devices with them at all times makes the J2ME platform a good candidate for implementing spatially enabled client software.

The spatially enabled J2ME client described can easily be used on most mobile phones and personal digital assistants (PDAs) available today and provides a nice addition to standard ArcIMS clients such as ArcExplorer or HTML-based map browsers.

About the Authors

Both Martin Brehovsky and Tomas Brandalik are employed by Sun Microsystems in Prague, Czech Republic, where they are working on an integrated development environment for Java and J2ME. Prior to joining Sun, Brehovsky was an assistant lecturer at the Department of Mathematics, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic, where he focused on GIS and distributed information systems. Tomas Brandalik worked as an application programmer for ARCDATA Praha, Esri's distributor in the Czech Republic.