Question

I created a Java code that tries to access the method LoadProject of the class IProjectFactory defined in myAPI.dll. The description of the DLL file says: IProjectFactory is used to load a project file into memory. IProjectFactory is a static class in the myAPI.dll assembly. It exposes the LoadProject method that takes a string containing the path to the file to load, and returns a reference to the resulting IProject. Using the IProject interface you can then manipulate the loaded project in various ways.

import com.sun.jna.Library;
import com.sun.jna.Native;

public class MyClass {

public interface IProjectFactory extends Library {
    public Object LoadProject(String fileName);
}

public MyClass() {
    //System.loadLibrary("myAPI");
    load();
}

void load() {
    String fileName = "xxx.sp";
    IProjectFactory api = (IProjectFactory) Native.loadLibrary("myAPI",IProjectFactory.class);

    try {
        Object project = api.LoadProject(fileName);
    }
    catch (Exception e) {
        e.printStackTrace();
    }
}

}

After running this code, the following error message has been generated:

Exception in thread "AWT-EventQueue-0" java.lang.UnsatisfiedLinkError: Error looking up function 'LoadProject': The specified procedure could not be found.

    at com.sun.jna.Function.<init>(Function.java:179)
    at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:350)
    at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:330)
    at com.sun.jna.Library$Handler.invoke(Library.java:203)
    at $Proxy0.LoadProject(Unknown Source)

Does it mean that myAPI does not contain the class IProjectFactory with the method LoadProject?

Answer 1

You can call functions in native libraries with JNI or JNA. Primitive types are mapped. Certain structures are possible also. Even callback functions are possible. See JNA’s mapping table.

What is impossible, by design: Getting a class or interface that was designed for a different runtime environment (like CLR) and use it seamless within the JVM.

So if you have a native procedural/functional library that just returns pointers or primitive types then you can use it quite well.

If you need to work with objects that are returned then you are out of luck. You need to run them in their native environment and find some way of interprocess communication.