我无法使用JNA以Java代码访问Visual Basic DLL方法

Question

I was pushed to use JNA (Java Native Access) in order to read data through Ehternet (based on UDP protocol). I've received, plugin UDP_RT.dll, programmed in visual basic. Now I'm trying to use this library in my Java code with JNA help. I went through a lot of tutorials, with some successful but some part of code doesn't work and now no clue what I can do next . I been able to load library, but can't solve puzzle how to use method from UDP_RT.dll, becouse I'm getting an error:

Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up function 'close': Nie można odnaleźć określonej procedury.
enter code here
at com.sun.jna.Function.<init>(Function.java:208)
at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:536)
at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:513)
at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:499)
at com.sun.jna.Library$Handler.invoke(Library.java:199)

I saw a lot of threads on stackoverflow like How to access DLL methods in Java code using JNA?

What I been able to figure out is that might be issue of UDP_RT.dll rather that my JAVA Code. I have to admit that I don't have a lot of experience with visual basic (only basic skills) also I don't have a UDP_RT.dll source code (but wheh I would be mandatory I think I may get). I've tried to load these methods in Visual Basic it seems load these methods. I looked to deinition of UDP_RT in visual and I can see some methods. Below I'm attaching screenshots, java code and visual basic code Thanks in advance for your help!

  interface UDP_RT extends Library {

    public boolean   Init(int a,int b ,int c,int d);
    void close();

    }


public class Native2{

    public static void main(String[] args) {
        UDP_RT UDP = (UDP_RT)Native.loadLibrary("UDP_RT2", UDP_RT.class,W32APIOptions.ASCII_OPTIONS);
        UDP.close();
        UDP.Init(9000, 8000, 1, 2);

    }
}

Answer 1

The Visual Studio Object Browser is showing you the assembly's .NET metadata. A .NET assembly does not usually have the same functions in its function export table. You can see the export table using Dependency Walker or CFF Explorer . If you don't see them, it means they aren't callable via the technique that you're trying.

You could write a JNI interface using a C++/CLI wrapper for the .NET assembly. C++/CLI is designed to intermix C++ and .NET. The wrapper functions can be exported as JNI implementations and their code can call the .NET methods. It's not too difficult if the methods you what to call are static or if the .NET objects you create will live only for the duration of a wrapper function call.

You should also consider using an interop library for .NET (eg, Javonet, JNBridge) or, if the assembly's object are exposed through COM an interop library for COM (eg, JNIWrapper). See Best way to call VB.NET function from Java? .

Answer 2

In JNI types are wrapped into adapter to be java-compatible. The methods must be named java-compatible too. Try to build your own dll to wrap/unwrap and load the dll indirectly.

Look for javah to create JNI compatible header-files.

A example here: http://www.sahirshah.com/java/jni.html

Answer 3

There exists a package called Unmanaged Export and it is very handy and easy to use! from the link you can access the docu via "Project Site"

With this package you can export C#, VB.NET or F# Methodes to Java via JNA (and nothing else). I gave a little more details in the following post: Call DLL from Java using JNA - which seems somekind related/similar to me

it helped me alot with my own project. tbh I never tried it with VB.NET just with C#, but as Robert Giesecke says in his docu, it should work with both. hope this helps. cheers