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Enterprise J2ME: End-to-end best practices

Conquer the challenges of mobile application development

By Michael Yuan, JavaWorld.com, 03/22/04

J2ME allows desktop or enterprise Java developers to migrate their existing skills to build smart mobile applications for enterprises and consumers. Those skills include basic concepts of the Java language, APIs, and common design patterns. However, blind "skill transfer" from the desktop, server, or thin-client world could do more harm than good. For example, although most AWT-based J2SE applications run on PersonalJava and J2ME Personal Profile without modification, porting them directly to mobile devices often results in unacceptable performance and very poor usability. To build successful smart mobile applications, developers must understand the special characteristics of mobile devices and networks.

As Java developers and architects, what should we know about the mobile development? How do we retrain ourselves for the new tasks? In this chapter, we analyze challenges in mobile application development and discuss best practices to overcome them.

Limited device hardware

The most visible difference between the mobile and PC platforms is the difference in computing hardware. Today's PCs have much faster CPUs and far more memory and storage spaces than any mobile computing device. Desktop and server developers can afford the luxury to write applications with bloated features (e.g., Microsoft Office); they also have access to rich productivity features provided by large, all-in-one frameworks (such as the J2SE platform itself). However, on mobile devices, it is a completely different story. With CPUs as slow as 20 MHz and RAM as little as 100 KB, we must carefully evaluate the features we need, thoroughly optimize our code, and live with limited framework support. In this section, we discuss how to cope with those challenges.

Lightweight libraries

The most common mistake beginners make is the "golden hammer" anti-pattern: choosing the wrong technology for the task. In the Java world, software tools are often available as reusable objects in standard or third-party libraries. To choose the best libraries that support required application features at the minimum hardware cost is essential.

J2ME Foundation and Personal Profiles (as well as PersonalJava) are compatible with J2SE at the bytecode level and inherit a large subset of the J2SE core API. In theory, we can port J2SE libraries (e.g., XML processing, cryptography, messaging, and UI) directly to mobile devices. However, to do so would defeat the purpose of J2ME and result in slow and bloated applications that can be deployed only to the most expensive devices. In most cases, we should choose from lightweight library alternatives that are specifically designed for the mobile platform. Multiple vendors often compete in the same market. Each vendor offers a slightly different lightweight product with an emphasis on different features.

CLDC (Connected Limited Device Configuration) and MIDP (Mobile Information Device Profile) standard libraries are designed from the ground up as lightweight components. However, the need to select the right tools also applies to MIDP projects when it comes to third-party libraries. For a specific library, vendors often offer a version with J2SE-compatible APIs for larger MIDP devices (e.g., Symbian OS devices) and another extremely lightweight version that uses proprietary APIs. The latter often has a smaller memory footprint and better performance, but requires extra developer training and results in less portable applications. Examples of MIDP lightweight libraries include the PointBase MIDP relational database APIs and iBus//Mobile JMS client APIs.

 

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