Java DLL linkage error

Question

I am using libusb-- http://sourceforge.net/apps/trac/libusb-win32/wiki

However, I get:

Exception in thread "main" java.lang.UnsatisfiedLinkError: USBManager.usb_init()V

public class USBManager 
{   
    static{
        System.loadLibrary("libusb");   
    }

    native void usb_init();
    public USBManager()
    {       
        usb_init();     
    } 
}

Answer 1

You can't just use public native usb_init(); and then load a native library like that, the JNI is not implemented that way.

you use javah to create a .h file the can be used to create a library that implements the specific native functions in the class.

javac USBManager

Creates a class file, that you use with javah:

javah USBManager

This yields a file in that location called 'USBManager.h', which specifies the functions to implement in a .so/.dll that implement the relevant native function.

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class USBManager */

#ifndef _Included_USBManager
#define _Included_USBManager
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     USBManager
 * Method:    usb_init
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_USBManager_usb_1init
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

So you need to export a function called 'Java_USBManager_usb_1init', that takes the to parameters specified.

That function can be nothing more than:

JNIEXPORT void JNICALL Java_USBManager_usb_1init (JNIEnv *, jobject) {
    usb_init();
}

There is a pretty good simple example on a blog by a Sun developer, but there are lots of other examples out there.