JNI Help!

Question

I am trying to build a simple test program to call a win32api dll.
Here's the code:
import java.util.*;
import java.lang.*;
public class JNItest
static
System.loadLibrary( "winmm" );
System.out.println( "Library loaded." );
static native long PlaySound(String lpszSound, long dwFlags, long fuSound);
public static void main (String args[])
long returnCode = 0;
long xx = 0;
long flags = 0;
String soundFile = "\\MEDIA\\The Microsoft Sound.wav";
System.out.println("Playing '" + soundFile + "'...");
returnCode = PlaySound(soundFile, xx, flags);
The code compiles fine, with no warnings. I then run javah -jni to build the header file. This also works fine.
When I run it, the static initializer fires and loads the native library without error. However, when I actually hit the line of code to call the PlaySound method I get the following exception: "java.lang.UnsatisfiedLinkError: PlaySound".
My path includes a link to c:\winnt\system32 where winmm.dll resides. If you move this dll the loadLibrary method will fail, so I know it is finding the dll.
??? Does anyone know why the call to PlaySound is failing?
Thanks,
alan

Answer 1

It failed because you cannot call a Win32 API function in Java without writing a wrapper dll. What you did is just creates a C/C++ header file.
As for why the static initializer successfully loads the dll is because the file exists.
All C/C++ codes for the native method should have something likeJNIEXPORT void JNICALL Java_HelloWorld_print(JNIEnv *env, jobject obj)As for your's, the function should beJNIEXPORT jlong JNICALL Java_JNItest_PlaySound(JNIEnv *env, jobject obj, jstring lpszSound, jlong dwFlags, jlong fuSound)For more information:
http://java.sun.com/docs/books/tutorial/native1.1/index.html