Question

I’m using Java for a small app. It’s a rewrite of an existing MFC project. There is an existing dll that I need to change to enable access from Java using JNI. All of this Java stuff is new to me, so I’m having a little trouble and feeling rather dense when I read other forum posts. In the existing dll I have a function like this:

extern "C" __declspec(dllexport) bool Create()
{
     return TRUE;
}

Dumb question time. How do I properly set it up to be called by Java?

I tried this:

JNIEXPORT jboolean JNICALL Create()
{
     return TRUE;
}

I’m including jni.h and everything compiles fine. However, when I call it from Java I get UnsatisfiedLinkError. I’m calling it from Java using this:

public static native boolean CreateSession();

System.load("D:\\JavaCallTest.dll");
Create();

Could someone kindly push me in the proper direction? I sincerely appreciate any help.

Thanks,

Nick

Answer 1

You need to include the Java class name and path in your native code, for example if your native method was declared in Java as:

public class NativeCode {
    public static native boolean CreateSession();
}

and the class path was (for example) com.example.NativeCode you would declare your method in native as follows:

extern "C"
JNIEXPORT jboolean JNICALL Java_com_example_NativeCode_CreateSession(JniEnv* env, jclass clazz)
{
    return JNI_TRUE;
}

All JNI methods have a JNIEnv pointer and class as their first two parameters.