Is JNI able to be multi-processing? and How can I receive Unicode from C-DLL?

Created May 4, 2012

Alexander Krapf

William,

JNI can be used in multithreaded applications. When you are calling into a C-DLL, there is always the possibility of the DLL not being able to work in a mult-threaded environment. Mutable global variables used in processing are usually a warning signal.

Specifically addressing your problem though:

Compare the Unicode character size used in your Oracle library to the definition of jchar in your platform-specific JNI include file. Make sure they are the same size.
How does Oracle return Unicode? As UTF-8 or as an array of Unicode characters? It needs to be the latter for NewString to work.
You can always try calling one of the String class' constructors that takes an encoding as an argument. That should work with whatever Oracle returns.
Check that you're not caching local or object or class references between invocations. That's forbidden in JNI and can result in exceptions.

You might also want to give our JunC++ion product a try. It's not free, but it removes many JNI headaches. Check it out at http://www.codemesh.com. Disclaimer: I am a principal at Codemesh.

Good luck,

Alex