Desktop java app copy and transfer android data via USB

Question

I have a desktop java app, and also an android app. Two app work together.

The user in desktop app have a button to launch the transfer between device data app to computer app and vice versa.

So I need to transfer data with a simple USB cable, and without internet connection/WiFi/Bluetooth/adb.

I found two Java MTP library that works on Windows to resolve my problem, and the USB Host/accesory fonctionnality of android:

• jMTP successfully recognizes my Android devices, folder, and other things

  I have success to transfer a file in computer ---> device, but i have an error when i try to transfer a file in device ---> computer

  I put my code after the explaination.

• jusbpmp but i don't have the possibility to transfer device ---> computer.

• USB Host/accesory not usefull because transfer are launch from desktop app, and when i read on the android developper guide website, it seems to be not correspond from what i need, or maybe if the user start transfer from the device.

I try from 1 week to success in this task but it seems i need help.

Java + jMTP code

private static void jMTPeMethode() 
        {
            PortableDeviceManager manager = new PortableDeviceManager();
            PortableDevice device = manager.getDevices()[0];
            // Connect to USB tablet
            device.open();

            System.out.println(device.getModel());

            System.out.println("---------------");

            // Iterate over deviceObjects
            for (PortableDeviceObject object : device.getRootObjects()) 
            {
                // If the object is a storage object
                if (object instanceof PortableDeviceStorageObject) 
                {
                    PortableDeviceStorageObject storage = (PortableDeviceStorageObject) object;

                    for (PortableDeviceObject o2 : storage.getChildObjects()) 
                    {
                        if(o2.getOriginalFileName().equalsIgnoreCase("Test"))
                        {

                            //Device to computer not working
                            PortableDeviceToHostImpl32 copy = new PortableDeviceToHostImpl32();
                            try 
                            {
                                copy.copyFromPortableDeviceToHost(o2.getID(), "C:\\TransferTest", device);
                            } catch (COMException ex) 
                            {

                            }

    //                      //Host to Device working
    //                      BigInteger bigInteger1 = new BigInteger("123456789");
    //                      File file = new File("c:/GettingJMTP.pdf");
    //                      try {
    //                          storage.addAudioObject(file, "jj", "jj", bigInteger1);
    //                      } catch (Exception e) {
    //                          //System.out.println("Exception e = " + e);
    //                      }
                        }
                        System.out.println(o2.getOriginalFileName());
                    }
                }
            }

            manager.getDevices()[0].close();
        }

This is the result of the code and the error

`

    Nexus 9
    ---------------
    Music
    Podcasts
    Ringtones
    Alarms
    Notifications
    Pictures
    Movies
    Download
    DCIM
    Android
    ! Failed to get IStream (representing object data on the device) from IPortableDeviceResources, hr = 0x80070057
    test
    ReleveData

`

I read in internet 0x80070057 is a generic windows exception .

Edit:

Windows site say for the hr error ERROR_INVALID_PARAMETER 0x80070057 : The parameter supplied by the application is not valid.

But i don't see witch parameter is not valid

---

Here is the link of C class of the library use for transfer data device to computer, you can see my error line 230.

And this is the jMTP library i use.

Can you help me, or purpose an other way to do what i need(Usb4Java, libUSB) ? I shall be really grateful.

Thanks by advance.

Answer 1

Ok, i found the problem.

The problem come from o2.getID() parameter give to the methode copy.copyFromPortableDeviceToHost.

Because o2 representing the folder, and not the file in the folder, so it's not possible to send folder, for success i need to send file in folder.

So i cast my PortableDeviceObject o2 to an PortableDeviceFolderObject, so that get a list of child Object with targetFolder.getChildObjects() in the PortableDeviceFolderObject representing files' and then i can iterate on any child objet from the folder.

And for each file i call the methode copy.copyFromPortableDeviceToHost, with the right id.

Here is the correction code, copy/transfer file from computer to device and device to computer.

I hope it's help.

public class USBTransfertMain {

    public static void main(String[] args) throws Throwable {
        jMTPeMethode();
    }

    private static void jMTPeMethode() 
    {
        PortableDeviceFolderObject targetFolder = null;
        PortableDeviceManager manager = new PortableDeviceManager();
        PortableDevice device = manager.getDevices()[0];
        // Connect to USB tablet
        device.open();
        System.out.println(device.getModel());

        System.out.println("---------------");

        // Iterate over deviceObjects
        for (PortableDeviceObject object : device.getRootObjects()) 
        {
            // If the object is a storage object
            if (object instanceof PortableDeviceStorageObject) 
            {
                PortableDeviceStorageObject storage = (PortableDeviceStorageObject) object;

                for (PortableDeviceObject o2 : storage.getChildObjects()) 
                {
                    if(o2.getOriginalFileName().equalsIgnoreCase("testFolder"))
                    {
                        targetFolder = (PortableDeviceFolderObject) o2;
                    }

                    System.out.println(o2.getOriginalFileName());
                }

                copyFileFromComputerToDeviceFolder(targetFolder);
                PortableDeviceObject[] folderFiles = targetFolder.getChildObjects();
                for (PortableDeviceObject pDO : folderFiles) {
                    copyFileFromDeviceToComputerFolder(pDO, device);
                }

            }
        }

        manager.getDevices()[0].close();
    }

    private static void copyFileFromDeviceToComputerFolder(PortableDeviceObject pDO, PortableDevice device)
    {
        PortableDeviceToHostImpl32 copy = new PortableDeviceToHostImpl32();
        try {
            copy.copyFromPortableDeviceToHost(pDO.getID(), "C:\\TransferTest", device);
        } catch (COMException ex) {
            ex.printStackTrace();
        }

    }

    private static void copyFileFromComputerToDeviceFolder(PortableDeviceFolderObject targetFolder) 
    {
        BigInteger bigInteger1 = new BigInteger("123456789");
        File file = new File("C:\\GettingJMTP.pdf");
        try {
            targetFolder.addAudioObject(file, "jj", "jj", bigInteger1);
        } catch (Exception e) {
            System.out.println("Exception e = " + e);
        }
    }
}