Best binary XML format for JavaME

You might want to take a look at wbxml (Wireless Binary XML) it is optimized for size, and often used on mobile phones, but it is not optimized for parsing speed.

What kind of data are you planning to use? I would say, that if the server is also done in Java, easiest way for small footprint is to send/receive binary data in predefined format. Just write everything in known order into DataOutputStream.

But it would really depend, what what kind of data are you working on and can you define the format.

Actually you should evaluate, if this kind of optimization is even needed. Maybe you target devices are not so limited.

Hessian might be an alternative worth looking at. It is a small protocol, well-suited for Java ME applications.

"Hessian is a binary web service protocol that makes web services usable without requiring a large framework, and without learning a new set of protocols. Because it is a binary protocol, it is well-suited to sending binary data without any need to extend the protocol with attachments."

More links:

Here

Here too