How to programmatically move , copy files to SD?

I am making an android app which lets the user transfer some files from internal storage to external storage(SD card) using SAF.

This is how I call an intent to let the user choose the SD card directory.

Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
intent.addFlags(Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
startActivityForResult(intent, 42);

And this is my onActivityResult

 public  void onActivityResult(int requestCode, int resultCode, Intent data) {      
    treeUri = data.getData();
    final int takeFlags = data.getFlags()
        & (Intent.FLAG_GRANT_READ_URI_PERMISSION
        | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
    getActivity().getContentResolver().takePersistableUriPermission(treeUri, takeFlags);
 }

I am taking permission for whole SD card so that i can move or delete any file in sd card any time .The problem is that even after taking permission i am not able to move or delete any file in SD card.

How should i move a file from internal Storage to external(SD card) for android 5.0 and above.

EDIT:This is the code i am using to move files.

public static void MoveFiles(File src, File dst) throws IOException
{
    FileChannel inChannel = new FileInputStream(src).getChannel();
    FileChannel outChannel = new FileOutputStream(dst).getChannel();
    try
    {
        inChannel.transferTo(0, inChannel.size(), outChannel);
    }
    finally
    {
        if (inChannel != null)
            inChannel.close();
        if (outChannel != null)
            outChannel.close();
           src.delete();
        
    }
}

This is how I finally solved the issue.

First call an intent to let the user grant write permission for whole SD card.

Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
        intent.addFlags(Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
        startActivityForResult(intent, 42);

Then on onActivityResult take write permission.

public  void onActivityResult(int requestCode, int resultCode, Intent data) {
    treeUri = data.getData();
    final int takeFlags = data.getFlags()
        & (Intent.FLAG_GRANT_READ_URI_PERMISSION
        | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
    getActivity().getContentResolver().takePersistableUriPermission(treeUri, takeFlags);
}

And this is the code I used to copy files to SD card.

public static boolean copy(File copy, String directory, Context con) {
    static FileInputStream inStream = null;
    static OutputStream outStream = null;
    DocumentFile dir= getDocumentFileIfAllowedToWrite(new File(directory), con);
    String mime = mime(copy.toURI().toString());
    DocumentFile copy1= dir.createFile(mime, copy.getName());
    try {
        inStream = new FileInputStream(copy);
        outStream =
                con.getContentResolver().openOutputStream(copy1.getUri());
        byte[] buffer = new byte[16384];
        int bytesRead;
        while ((bytesRead = inStream.read(buffer)) != -1) {
            outStream.write(buffer, 0, bytesRead);

        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {

            inStream.close();

            outStream.close();


            return true;


        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return false;
}

The above code uses the following two methods.

getDocumentFileIfAllowedToWrite method which returns DocumentFile if allowed to write.

public static DocumentFile getDocumentFileIfAllowedToWrite(File file, Context con) {
    List<UriPermission> permissionUris = con.getContentResolver().getPersistedUriPermissions();

    for (UriPermission permissionUri : permissionUris) {
        Uri treeUri = permissionUri.getUri();
        DocumentFile rootDocFile = DocumentFile.fromTreeUri(con, treeUri);
        String rootDocFilePath = FileUtil.getFullPathFromTreeUri(treeUri, con);

        if (file.getAbsolutePath().startsWith(rootDocFilePath)) {

            ArrayList<String> pathInRootDocParts = new ArrayList<String>();
            while (!rootDocFilePath.equals(file.getAbsolutePath())) {
                pathInRootDocParts.add(file.getName());
                file = file.getParentFile();
            }

            DocumentFile docFile = null;

            if (pathInRootDocParts.size() == 0) {
                docFile = DocumentFile.fromTreeUri(con, rootDocFile.getUri());
            } else {
                for (int i = pathInRootDocParts.size() - 1; i >= 0; i--) {
                    if (docFile == null) {
                        docFile = rootDocFile.findFile(pathInRootDocParts.get(i));
                    } else {
                        docFile = docFile.findFile(pathInRootDocParts.get(i));
                    }
                }
            }
            if (docFile != null && docFile.canWrite()) {
                return docFile;
            } else {
                return null;
            }

        }
    }
    return null;
}

And mime method which returns the mime type of the file.

   public static String mime(String URI) {
       static String type;
       String extention = MimeTypeMap.getFileExtensionFromUrl(URI);
       if (extention != null) {
           type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extention);
       }
       return type;
   }

I have tested the above code with Android Lollipop and Marshmallow.

EDIT: This is the link to the FileUtils class.