Guidelines for when to use JNI

Question

I didn't find an answer to this in any FAQ or the 2 JNI books I have, so apologies in advance if this is a common question whose answer has already been posted -
Do any guidelines exist for when, and to what extent, JNI should be used?
I'm currently working on my second project where the question of whether or not to use it has come up. Both projects were distributed and contained both C++ and Java code in different areas. The issue came up when the need arose to implement a new shared library that had to be used by both C++ and Java code. Logging and configuration services are examples of the new functionality.
The choice is whether to implement the new libraries primarily in C++ and supply a Java interface, via JNI, for Java code which needs to use it, or to implement the new libraries in both C++ and Java to support both types of clients.
On the previous project, a team member had extensive JNI experience and recommended the dual language implementation approach instead of JNI. This worked out ok except we did have to have to ensure the new library developer was skilled in both C++ and Java, and he had to be sure to update both when changes to 1 were necessary - a maintenance problem. The experienced JNI developer made this recommendation due to issues he had encountered previously - most notably issues related to errors in the native code which brought down the JVM.
On the current project, we're opting for base C++ implementations with JNI wrappers. That's making me somewhat nervous since the alternative seems safer.
What do other developers think?

Answer 1

Have you checked out www.javaworld.com. They usually have very good and in-depth articles. IMHO, it all depends on the sort of use your library is intended for. If its used extensively by native code, use C++ with a Java wrapper. It its the other way around, implement it in Java and use a JNI interface for native code. I would really consider this carefully before implementing stuff in C++ that is used from Java. First of all, Java is after all much simpler than C++, its a more elgant OO-language and you have the platform neutrality. On the other hand, C++ has its sides. I dont use JNI unless its absolutely neccessary, in situations like using legacy code.
These are just a few of my thoughts, hope it gives you some hints.