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The Challenges of Porting a Java ME Application to Multiple Devices

Coping with idiosyncrasies, the unexpected, and complexity

However, it's important to keep the code clean of directives that refer to device names. Instead, the directives should refer to semantic capabilities of the application. For example, Device Y requires a slightly different address format in the communications module than all other devices due to its using a different communications protocol. Instead of having code like:

#if DEVICE=="Y"
address = formatDifferentAddress(address);
#endif

sendMessage(address,portNumber,content);

the code should read:

#if COMM_PROTOCOL=="XYZ"
address = formatDifferentAddress(address);
#endif

sendMessage(address,portNumber,content);

The different behaviors should be extracted out as capabilities, and devices are attributed with these capabilities. For each device there will be a configuration file that contains details of the capabilities that the device requires, which, at build time, is translated into the correct preprocessor definitions. Table 1 illustrates an example device capability file. Observe that some of the capabilities are feature-based in that each device is expected to have a different value, like screen settings, and other capabilities are the result of bugs in the system. For example, a bug in the RMS writing module on a certain device could have resulted in special code that writes data at set intervals, which results in the RMS_WRITE_INTERVAL_MS capability.

Since ant is the most common way to build Java applications, it's recommended that this file be a properties file (see Table 2).

As with most tasks in the Java world, there's a tool that can help you manage device capabilities. J2MEPolish is an advanced open source build tool and GUI framework for Java ME applications and currently has a database of nearly 400 devices with a lot of predefined capabilities. Another recently released open source library, the J2ME Device DB project, boasts capabilities similar to J2MEPolish and is worth evaluating. There are also several commercial packages available that address these problems that can be found on the Web.

Flexible Builds
Having a Java ME application that's supported on a large number of devices means that you have to make a large number of builds when releasing versions for testing or QA. Manually building devices might be acceptable for a few devices, but when the number increases, you'll have to have a way of batch building applications for all devices or for a particular subset of devices. Again, J2MEPolish has a good ant-based build framework sufficient for most needs.

However, when each customer needs multiple languages, and possibly different feature sets, the build process will get more complicated. For each device there might be different language options combined with several different feature sets that have to be built. The difficulty of managing which configurations to build for which customer becomes increasingly relevant and a solid, flexible build is mandatory to carry the project through this complexity

Conclusion
Porting Java ME applications can be scary, but with a lot of preparation and research, Java ME applications can be successfully ported to multiple devices. Fears about being swamped by the unmanageable number of problems that are encountered in different devices can be silenced. The ME project, which could so easily have ended in failure, can now be tackled with the same confidence that one has undertaking a regular Java project.

References

  • J2MEUnit - http://j2meunit.sourceforge.net
  • JUnit - www.junit.org
  • J2MEPolish - www.j2mepolish.org
  • J2ME Device DB project - http://j2me-device-db.sourceforge.net
  • More Stories By Hayden Marchant

    Hayden Marchant is a Software Engineer in the Information Integration Solutions group at IBM. He has 10 years of experience in software engineering. Hayden has a 1st class honors BA in mathematics from Cambridge University, England, and is a Sun Certified Programmer.

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