Is it possible to call a non-JNI DLL

Question

I have a DLL I'd like to execute from Java, but do not have access to the source. From what I've read about JNI, it seems it requires Java specific code in the DLL source. Is there any other option? I need to pass it a String and it returns a String. Is Runtime.exec a viable option?
Any advice would be greatly appreciated.

Answer 1

OK... here is a scenario with some code snippets. I've done this with a C/C++ dll on windows....so if ur on some other OS you'll have to make appropriate changes(ditto for DELPHI).
I have a dll called "myold.dll" written in C/C++ which has the following function signature
int getVersion();
My purpose is to call this function in the dll using JNI.
For this you will need
1. Header file of myold.dll (say myold.h)
2. .lib file for myold.dll (say myold.lib)
Now, write a java file "Mynative.java"
public class Mynative {
public native int getVersion();
   static {
      System.loadLibrary("Mynative"); //matches name of  new dll you are about to create
   public static void main(String[] args){
      Mynative nativity = new Mynative();
      int version = nativity.getVersion();
      System.out.println(version);
}after compiling the above code, you will need to run javah
on the resulting class file
javah -jni Mynative
Now you will have a header file Mynative.h which looks like
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class Mynative */
#ifndef IncludedMynative
#define IncludedMynative
#ifdef __cplusplus
extern "C" {
#endif
* Class: Mynative
* Method: getVersion
* Signature: ()I
JNIEXPORT jint JNICALL Java_Mynative_getVersion
(JNIEnv *, jobject);
#ifdef __cplusplus
#endif
#endif
Now create a C file say myCfile.c as follows
#include <jni.h>
#include "Mynative.h"
#include <stdio.h>
#include "windows.h"
#include "myold.h" //Header file of the existing dll..you need this file!!
JNIEXPORT jint JNICALL
Java_Mynative_getVersion(JNIEnv *env, jobject obj)
jint myInt;
/* Call native function in Mynative.dll */
myInt = getVersion();
printf(myInt);
printf("\n");
return myInt;
Now compile this file using a C compiler to create "mynative.dll".You'll have to know how to do that using whatever C/C++ compiler you use.
This dll should be in any folder thats on the Java Classpath or else you are going to get an error.
Well..you're set. You can run the java file and see the output.
If however you do not have the header file for myold.dll, then you'll have to know how to dynamically load a dll in C/C++. Unfortunately, i don't know how so u'll have to ask someone else.
Hope my efforts here don't go wasted. Good luck
Vinny.