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Is there any good tool to generate java (+JNI support if needed) from a header file so that a C or C++ library can be used as-is. Kind of a reverse of javah. The real functionality would be in the C/C++, the Java would be only a shim on top for certain users.
I'm no expert on JNI but as far as I can see Javah forces you to do this back to front. It forces you to have JNI-isms penetrating unecessarily into the C code unless you write a conversion layer yourself. And writing a conversion layer by hand is basically a waste of time, since all the information is there in the header file to begin with.
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javah generates C header and source files that are needed to implement native methods. The generated header and source files are used by C programs to reference an object's instance variables from native source code. The . h file contains a struct definition whose layout parallels the layout of the corresponding class.
In C language, header files contain the set of predefined standard library functions. You request to use a header file in your program by including it with the C preprocessing directive “#include”. All the header file have a '. h' an extension. By including a header file, we can use its contents in our program.
You can tell javah to place the header files in a different directory with the -d option. The name of the header file is the Java class name with a . h appended to the end of it. For example, the command shown above will generate a file named HelloWorld.
If you are including a C header file that isn't provided by the system, you may need to wrap the #include line in an extern "C" { /*... */ } construct. This tells the C++ compiler that the functions declared in the header file are C functions.
For C, you can use JNA. You do have to declare function signatures redundantly in Java, but do not have to write any glue code. JNA is very easy to use.
For C or C++, you can use SWIG. SWIG is a little more complex to use, but automatically generates Java wrappers for C++ classes. I'm enjoying it.
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JNAerator does exactly that : it reads C/C++/ObjectiveC headers and outputs Java bindings that rely on BridJ (C/C++), JNA (C only) or Rococoa (ObjectiveC, uses JNA).
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