Talking with the hardware in Java

I am missing to know how to talking with the hardware in Java, such as sending/receiving a stream of data to/from a device.

I had a university project about service oriented architecture, where a mobile device (Java enabled mobile phone or PDA) needs to interacts with a PC.

There must be a way to achieve that, but I could not find any sample code / help on the Net.

Some has suggested using the windows APIs and JNI. First of all I do not how to do that and I am not convinced that it is the only way!

It is hard to understand this short-coming in Java API.

Thanks in advance to anyone who may post useful solution or suggestion. Even a link to a solution will be much appreciated.