JNI: passing integer array from Java to C

Edit: Skip to part 2 for a simpler code.

Part 1: I am working on a project wherein I have to call Java routines from C++.

I use the following code to call the java method. The parameter is a string array from which the first 2 values are used to read a file from the hard drive decode it and return the data. For testing purpose, I am returning a 1D integer array containing only the first image in the file. There are more images in the file with Z depth and time sequence like in a video, ignoring those for now.

    mid = m_pJVMInstance->m_pEnv->GetStaticMethodID(imageJ_cls, "getIntData", "([Ljava/lang/String;)[I");
    if (mid == nullptr)
        cerr << "ERROR: method not found !" << endl;
    else {
        jobjectArray arr = m_pJVMInstance->m_pEnv->NewObjectArray(2,      // constructs java array of 2
            m_pJVMInstance->m_pEnv->FindClass("java/lang/String"),    // Strings
            m_pJVMInstance->m_pEnv->NewStringUTF("str"));   // each initialized with value "str"
        m_pJVMInstance->m_pEnv->SetObjectArrayElement(arr, 0, m_pJVMInstance->m_pEnv->NewStringUTF("D:\Dev_Environment\Test_Files\\"));  // change an element
        m_pJVMInstance->m_pEnv->SetObjectArrayElement(arr, 1, m_pJVMInstance->m_pEnv->NewStringUTF("4D_1ch.lsm"));  // change an element
        jintArray depth = (jintArray)(m_pJVMInstance->m_pEnv->CallStaticIntMethod(imageJ_cls, mid, arr));   // call the method with the arr as argument.

        m_pJVMInstance->m_pEnv->DeleteLocalRef(arr);     // release the object
    }

The method mid is getting the correct function. The Java code does some processing and returns a integer array to C++ for further processing.

The Java code:

public static int[] getIntData(String[] args) {
    int[] test = new int[1];
    test[0] = 1;
    String dir = args[0];
    String name = args[1];
    String id = dir + name;
    ImageProcessorReader ip_reader = new ImageProcessorReader(
            new ChannelSeparator(LociPrefs.makeImageReader()));
    try {
        IJ.showStatus("Examining file " + name);
        ip_reader.setId(id);
        int num = ip_reader.getImageCount();
        int width = ip_reader.getSizeX();
        int height = ip_reader.getSizeY();
        ImageStack stack = new ImageStack(width, height);
        byte[][][] lookupTable = new byte[ip_reader.getSizeC()][][];

        //TODO: Don't know how to handle multiple channels i.e RGb images currently.
        // Adding all the slices into a 2D array and returning those values.
        int[] test_array = new int[width*height];
        int[][][] return_array = new int[height][width][num];
        for (int i=0; i<num; i++) {
            IJ.showStatus("Reading image plane #" + (i + 1) + "/" + num);
            ImageProcessor ip = ip_reader.openProcessors(i)[0];

            // Copying the value to the return array.
            int[][] temp_array = ip.getIntArray();
            for (int h=0; h < height; h++) {
                for (int w = 0; w < width; w++) {
                    return_array[h][w][i] = temp_array[h][w];
                    if (i==0){
                        test_array[h*width + w] = temp_array[h][w];
                    }
                }
            }

            //java.awt.image.BufferedImage awt_Ip =  ip.getBufferedImage();
            //ImageIO.write(awt_Ip, "jpg", new File("D:\\Dev_Environment\\Test_Files\\Test_Folder\\out" + Integer.toString(i) + ".jpg"));

            stack.addSlice("" + (i + 1), ip);
            int channel = ip_reader.getZCTCoords(i)[1];
            lookupTable[channel] = ip_reader.get8BitLookupTable();
        }
        IJ.showStatus("Constructing image");
        ImagePlus imp = new ImagePlus(name, stack);

        // ImagePlus show is leading to java window not responding, maybe it is because this program is not a imageJ plugin but a standalone program.
        //imp.show();

        //ImagePlus colorizedImage = applyLookupTables(r, imp, lookupTable);
        //r.close();
        //colorizedImage.show();
        IJ.showStatus("");
        test[0] = 2;
        return test;
    }
    catch (FormatException exc) {
        IJ.error("Sorry, an error occurred: " + exc.getMessage());
        test[0] = 3;
    }
    catch (IOException exc) {
        IJ.error("Sorry, an error occurred: " + exc.getMessage());
        test[0] = 4;
    }
    return test;
}

For testing only I added a test array of size 1 to check the output in C++. I am getting 0 as a return value in the depth variable.

My question is how do we return an integer array from Java to c++? Is jintArray the right way? Consequently, can I return a 3D array from Java to C++?

Edit Part 2: I did a test with new Java code and same C++ code, except now I am calling "getInDataS" from the java side. Here is the java code:

    public static int[] getIntDataS(String[] args) {
    int[] test = new int[10];
    test[0] = 10;
    test[1] = 10;
    test[2] = 10;
    test[3] = 10;
    test[4] = 10;
    test[5] = 10;
    test[6] = 10;
    test[7] = 10;
    test[8] = 10;
    test[9] = 10;
    return test;
}

I am atleast getting some value in the depth variable but as soon as I try to read the values access violation is thrown. Bothe the lines of code throw the error. Here is the C++ Code:

jintArray depth = (jintArray)(m_pJVMInstance->m_pEnv->CallStaticIntMethod(imageJ_cls, mid, arr));
jsize len = m_pJVMInstance->m_pEnv->GetArrayLength(depth);
jint* body = m_pJVMInstance->m_pEnv->GetIntArrayElements(depth, 0);