从.dll创建.jar

Question

I'm currently trying to create a .jar from a .dll, in order to use it on Android applications. I'm quite new with this technology, so I'll tried to be as clear as possible.

I have 3 distinct parts:

• A first .dll which is an API, in C++ and developed with Visual studio 2013.
  
• A second .dll that makes the link between my API and Java code (using JNI, so this is my native library), also developed with Visual studio 2013.
  
• And my Java code that loads my native library and that implements native functions from API. I use eclipse IDE for that stuff, because I read somewhere that was the easiest way to create a .jar.
  

This part works pretty well. I created a main test and I get all the information from the API in Java. But now, I would like to create a .jar file that I can use on Android and here comes the crows...

I tried many ways, from the simple .jar export, to the One-Jar method, but nothing worked. I always have a link error on my android platform (functions are recognized on the .jar, but their implementations are not).

So here is my question, how to create a kind of 'static library' in a .jar that I can use on Android?

I hope I was clear enough, don't hesitate to ask me more details.

Thank you for your help!

EDIT:
I tried with an Android Library project and my problem is always coming from my loadLibrary() function:

public class MyWrapper {
    static {
        System.loadLibrary("MyWrapper");    
    }

    public static native int getNegative(int p_number);
    public static native int getPositive(int p_number);
}

Every things works fine on my library, but when I use it in android application, I always get this error:

01-27 11:31:29.565: E/AndroidRuntime(7089): FATAL EXCEPTION: main
01-27 11:31:29.565: E/AndroidRuntime(7089): Process: com.example.wrappertest, PID: 7089
01-27 11:31:29.565: E/AndroidRuntime(7089): java.lang.UnsatisfiedLinkError: Couldn't load MyWrapper from loader dalvik.system.PathClassLoader[DexPathList[[zip file "/data/app/com.example.wrappertest-2.apk"],nativeLibraryDirectories=[/data/app-lib/com.example.wrappertest-2, /vendor/lib, /system/lib]]]: findLibrary returned null

My library cound't be created as static library, to keep the link on the .dll?

Answer 1

A .dll file is usually windows specific. If you're wanting to load native code on Android you'll have to look into using the Native Development Kit. The specifics of using the NDK is a bit beyond what can be explained here, but the Android Developer website provides a decent starting point at http://developer.android.com/tools/sdk/ndk/index.html

As for the jar itself, you may want to look into building an Android Library Project instead. This is essentially a means of packaging a jar with some assets (including native libraries) which can be used by an Android Application project.

Answer 2

1. Compile your librarie with ndk-build
2. Create an Android Library module
3. Create a Java class and JNI wrapper
4. Disable gradle for ndk-build and create Android.mk and Application.mk in the jni folder
5. Import the .so library and pre build it on the Android.mk
6. Invoke ndk-build manually and its done