Java / JNI / MSVC java.lang.UnsatisfiedLinkError到我的DLL函数

Question

I'm writing a video encoder wrapper of libvpx for work, but in Java, when I try and call these functions, I get java.lang.UnsatisfiedLinkError.

Here is my Java code:

package default;

class YE_Vpx {
    native int create_stream( String path, int w, int h, int fps );
    native void finalize_stream( int streamid );
    native void append_stream( int streamid, int[] pixels );
    native void finalize_streams( );

    static {
        System.loadLibrary("libvpx_ye"); // This loads the DLL just fine (windows 7), otherwise it would tell me it wasn't in the java.library.path
    }
}

Here is my C Header (generated by javah):

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

#ifndef _Included_YE_Vpx
#define _Included_YE_Vpx
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     YE_Vpx
 * Method:    create_stream
 * Signature: (Ljava/lang/String;III)I
 */
JNIEXPORT jint JNICALL Java_YE_1Vpx_create_1stream
  (JNIEnv *, jobject, jstring, jint, jint, jint);

/*
 * Class:     YE_Vpx
 * Method:    finalize_stream
 * Signature: (I)V
 */
JNIEXPORT void JNICALL Java_YE_1Vpx_finalize_1stream
  (JNIEnv *, jobject, jint);

/*
 * Class:     YE_Vpx
 * Method:    append_stream
 * Signature: (I[I)V
 */
JNIEXPORT void JNICALL Java_YE_1Vpx_append_1stream
  (JNIEnv *, jobject, jint, jintArray);

/*
 * Class:     YE_Vpx
 * Method:    finalize_streams
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_YE_1Vpx_finalize_1streams
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

And here is my C code (which references other files that I don't think I can present here):

#include <jni.h>
#include <jni_md.h>
#include <sys/types.h>

#include "ye_vpx.h" // This is the javah generated header
#include "ye_vpx_c.h" // This is where most of the meat is, I can't actually post this file =/

#ifdef __cplusplus
extern "C" {
#endif

JNIEXPORT jint JNICALL Java_YE_1Vpx_create_1stream( JNIEnv *env, jobject obj, jstring path, jint w, jint h, jint fps )
{
    jboolean iscopy;
    const jchar *m_path = (*env)->GetStringChars(env, path, &iscopy);
    jint ret = ye_vpx_create_stream( (const char *)m_path, w, h, fps );
    (*env)->ReleaseStringChars(env, path, m_path);
    return ret;
}

JNIEXPORT void JNICALL Java_YE_1Vpx_finalize_1stream(JNIEnv *env, jobject obj, jint streamid)
{
    ye_vpx_finalize_stream( streamid );
}

JNIEXPORT void JNICALL Java_YE_1Vpx_append_1stream(JNIEnv *env, jobject obj, jint streamid, jintArray pixels)
{
    jint *px = NULL;
    int length = 0;

    length = (*env)->GetArrayLength(env, pixels);
    px = (jint *)calloc( length, sizeof(jint) );
    (*env)->GetIntArrayRegion(env, pixels, 0, length, px);
    //px = (jint *)GetIntArrayElements( env, pixels, &iscopy );
    ye_vpx_append_stream( streamid, px );
    free( px );
}

JNIEXPORT void JNICALL Java_YE_1Vpx_finalize_1streams(JNIEnv *env, jobject obj)
{
    ye_vpx_finalize_streams();
}

#ifdef __cplusplus
}
#endif

As far as I'm aware, I've exported everything necessary and properly. I'm using Microsoft Visual C (2010 Express), and am linking against jvm.lib and jawt.lib, and am statically linking against the MFC and ALT libraries. Did I miss anything?

I should mention while building my DLL, I get the following output:

1> Creating library C:\\Users\\Alexander\\youeye-rnd\\java-rnd\\libvpx-youeye\\msvc\\libvpx_ye\\Debug\\libvpx_ye.lib and object C:\\Users\\Alexander\\youeye-rnd\\java-rnd\\libvpx-youeye\\msvc\\libvpx_ye\\Debug\\libvpx_ye.exp

1>LINK : warning LNK4098: defaultlib 'LIBCMT' conflicts with use of other libs; use /NODEFAULTLIB:library 1> libvpx_ye.vcxproj -> C:\\Users\\Alexander\\youeye-rnd\\java-rnd\\libvpx-youeye\\msvc\\libvpx_ye\\Debug\\libvpx_ye.dll

I have tried setting "Ignore Specific Default Libraries" (under Linker > Input) to "/NODEFAULTLIB:libcmt" which had no effect. I think this may be my issue, but I'm not absolutely sure.

Answer 1

So there were two issues that made this difficult to debug, but both were sort of my fault.

First, when I made my original JNI c-header, I did not include the package name in the *.Java source, as I believed that the generated DLL file was sort of ambiguous to what package, as long as it understood the class it's functions related to. So, I added the proper package name, redid javah on the class, and it regenerated the header with the proper package name.

Second, to resolve the msvc issue, under Properties > Linker > Input > "Ignore Specific Default Libraries" I was putting in the full command line switch "/NODEFAULTLIB:libcmt" when it was only expecting me to put in libcmt and it took care of the rest. Once that was corrected, it compiled without any warnings.

I hope this helps some people debug their own JNI/DLL issues on windows.