JNI UnsatisfiedLinkError

Question

Hi everybody.
i've got a problem running a simple example of JNI.
I'm trying to call the method MessageBox of user32.dll, that is placed on system32 of course.
This is the code:
import java.io.*;
public class NativeMFCMsg{
static {
try {
//System.loadLibrary("user32");
System.load("c:\\winnt\\system32\\user32.dll");
System.out.println("Library user32 Loaded");
}catch(Exception e){
e.printStackTrace();
public native int MessageBox( int hWnd,String lpText,String lpCaption,int uType );
public static void main(String[] args){
try {
new NativeMFCMsg().MessageBox(0,"Hello","Caption",0);
}catch(UnsatisfiedLinkError ex){
ex.printStackTrace();
System.out.println("Error " + "\n" + ex.toString());
System.exit(1);
the load or the loadLibrary methods works fine ... the problem is when i call the MessageBox ... don't know why ? i've read the JNI tutorial from sun and i think that there is everything correct but ... it's obvious that i'm wrong ...
please help.
Regards, Roberto.

Answer 1

First, you could use the -verbose option of the jvm to try to get some more info. Is there is some other dll that it can't find ?
Then, you could check your method signature. Make sure you use the prototypes from the JNI-created header file exactly.
In particular, did you supply the fully qualified name (including the package name) of your class to javah (e.g. yourPackage.yourClass).
The mangled name (in yourPackage_yourClass.h) should look like this:
Ljava_yourPackage_yourClass_yourMethod