从Java呼叫86x Dll

Question

Am trying to call a x86 DLL that I created using VC 6, from a java project on Eclipse, first try I got an error saying that I can't call a x86 DLL from a x64 envirement and that the DLL can't be loaded. So I installed a x86 jre and I have no more problem to charge the DLL. But when I try to call my c++ function I get the following exception:

     Exception in thread "main" java.lang.UnsatisfiedLinkError: mm.SimpleDLL.SimpleDLL_Calculation_Add(II)I

Can someone please help me ? Thank you.

SimpleDLL.h

    #ifndef SIMPLE_DLL_H
    #define SIMPLE_DLL_H

    namespace SimpleDll
    {

    extern class Calculation
    {
    public:
     static __declspec(dllexport) int Add(int a, int b);
    };
    }

    #endif SIMPLE_DLL_H

SimpleDLL.cpp

    #include "SimpleDll.h"

    namespace SimpleDll
    {

       int Calculation::Add(int a, int b)
      { return a + b; }

    }

SimpleDLL.java

    package mm;

    public class SimpleDLL {

        static
        {
            System.load("D:\\SimpleDLL.dll");   
        }
        public static void main(String ar[])
        {
            System.out.println("Hello world from Java");
            SimpleDLL t=new SimpleDLL();
            int x = t.SimpleDLL_Calculation_Add(6, 7);
            System.out.println("Resultat  "+x);
        }
        public native int SimpleDLL_Calculation_Add(int a, int b);
    }

Exported DLL Functions View

Resolved using the JNA library, I used this link to walkthrough

Answer 1

You need to build a 32-bit DLL and a .h file using javah for the exact signature Java expects. It is usually something like

JNIEXPORT jboolean JNICALL Java_Sample1_booleanMethod
  (JNIEnv *, jobject, jboolean);

from https://medium.com/@bschlining/a-simple-java-native-interface-jni-example-in-java-and-scala-68fdafe76f5f

An alternative approach is to use a library like JNA or JNR-FFI which allow you to bind to a C library without writing this bridging code.