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Thread: Using JNA to access export native classes

  1. #1
    Join Date
    May 2011

    Unhappy Using JNA to access export native classes

    Hi everyone,

    Currently I am working on java project which uses methods and classes present inside a DLL. Suppose I have such a method inside the DLL(named MyDLL.dll):

    Method inside my DLL code
    extern "C" __declspec(dllexport) int myMethod();

    corresponding JNA implementation
    import com.sun.jna.Library;
    import com.sun.jna.Native;
    import com.sun.jna.Platform;

    /** Simple example of native library declaration and usage. */
    public class HelloWorld {
    public interface CLibrary extends Library {
    CLibrary INSTANCE = (CLibrary) Native.loadLibrary("MyDLL", CLibrary.class);
    int myMethod();

    public static void main(String[] args) {
    String libPath = "path to MyDLL.dll";
    System.setProperty("jna.library.path", libPath);
    int RetVar = CLibrary.INSTANCE.myMethod();
    } ////main function ends

    } ////class ends

    So, my doubt is that like the function present inside the DLL, I have also got a class inside the DLL which needs to be exported:

    Class inside my DLL code
    extern "C" __declspec(dllexport) Class myClass
    //////code inside class

    So, now the question is how I am gonna use this native class inside my java code like i did for the native method?

  2. #2
    Join Date
    May 2011

    Question Re: Using JNA to access export native classes

    Or I have an alternative doubt to it:

    if the method inside my DLL is declared as follows:
    extern "C" __declspec(dllexport) int myMethod();

    that means i just need to declare a native equivalent of 'myMethod' to use it in my java code like:

    public native int myMethod();

    Now i can call the function as follows: int var = myMethod();

    //********************Now the NEW part***********************\\

    Inside the DLL, now I also have a class along with the method as follows:

    class MyClass
    int var;

    extern "C" __declspec(dllexport) MyClass __cdecl myMethod()
    MyClass obj;
    obj.var = 45;
    return obj;
    ///////////////////////////DLL code ends\\\\\\\\\\\\\\\\\\\\\\\\

    I hope you all noticed that now my return type is an object of a class rather than a normal int.

    So, now the bigger question is, how I am going to use this native function (myMethod) inside my JAVA code? Previously the return type was just an integer, so it was easy. But now what or rather how?

    See, I have mentioned my 2 doubts. So, clarification of either of the doubt will do.

    It's very urgent. So, i would really be grateful if someone can provide me with any kind of solutions or helpful links?

    Thanks in advance,

    With regards,
    Satya Prakash.

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