2010/01/28 creating JNI with Swig
I am currently playing around with JNI and Java due the colleagues question to make the connect features of jack-audio (http://jackaudio.org) accessible to java.
There is already a javalib (http://jjack.berlios.de) with some features, there seems still some needes ones missing.
So i started today to have a look into SWIG (http://swig.org).
“SWIG is a software development tool that connects programs written in C and C++ with a variety of high-level programming languages.”
After some hours of research i ended up with some facts:
To created yourself a Java binding to a given c/c++ Program or Library you need one or more Interface files (*.I) and swig file with all the necessary swig module descriptions.
There is an example on the swig homepage ( http://www.swig.org/Doc1.3/SWIGDocumentation.html#Introduction) to explain the workflow of SWIG.
There is a c file exmple.c:
/* File : example.c */
double My_variable = 3.0;
/* Compute factorial of n */
int fact(int n) {
if (n <= 1)
return 1;
else
return n*fact(n-1);
}
/* Compute n mod m */
int my_mod(int n, int m) {
return(n % m);
}
The mapping example.i files looks as the following:
/* File : example.i */
%module example
%{
/* Put headers and other declarations here */
extern double My_variable;
extern int fact(int);
extern int my_mod(int n, int m);
%}
extern double My_variable;
extern int fact(int);
extern int my_mod(int n, int m);
As you can see, the Interface file has a similar syntax with some additional meta information.
You can now create your JNI bindings:
swig -java example.i There are also flags for different other languages: -allegrocl - Generate ALLEGROCL wrappers -chicken - Generate CHICKEN wrappers -clisp - Generate CLISP wrappers -cffi - Generate CFFI wrappers -csharp - Generate C# wrappers -guile - Generate Guile wrappers -java - Generate Java wrappers -lua - Generate Lua wrappers -modula3 - Generate Modula 3 wrappers -mzscheme - Generate Mzscheme wrappers -ocaml - Generate Ocaml wrappers -octave - Generate Octave wrappers -perl - Generate Perl wrappers -php - Generate PHP wrappers -pike - Generate Pike wrappers -python - Generate Python wrappers -r - Generate R (aka GNU S) wrappers -ruby - Generate Ruby wrappers -sexp - Generate Lisp S-Expressions wrappers -tcl - Generate Tcl wrappers -uffi - Generate Common Lisp / UFFI wrappers -xml - Generate XML wrappers
As a result you get three new files:
- example.java
- exampleJNI.java
- example_wrap.c
The example_wrap.c can be used to compile the needed library file for your JNI access.
The two java Files are the basic JNI implementation:
class exampleJNI {
public final static native void My_variable_set(double jarg1);
public final static native double My_variable_get();
public final static native int fact(int jarg1);
public final static native int my_mod(int jarg1, int jarg2);
}
And a basic java example how to access these functions:
public class example {
public static void setMy_variable(double value) {
exampleJNI.My_variable_set(value);
}
public static double getMy_variable() {
return exampleJNI.My_variable_get();
}
public static int fact(int arg0) {
return exampleJNI.fact(arg0);
}
public static int my_mod(int n, int m) {
return exampleJNI.my_mod(n, m);
}
}
To get into working with SWIG i can advise the sources of the G4Java Project.
There is also a maven plugin to use SWIG from within your maven build: http://java.freehep.org/freehep-swig-plugin.
I am currently trying to create the necessary Interface files from the jack-audio sources to use them for a first run of SWIG. For python and tck you can use cmake to create these files.
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