The code above should actually be:

            // Write the file
                    OutputStream outputStream = getContentResolver().openOutputStream(currentUri);
            OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream );


Actually the problem seems to be with ParcelFileDescriptor.AutoCloseOutputStream .  I can get the code above to work fine if I don't use getContentResolver().openOutputStream(currentUri) , which returns a  ParcelFileDescriptor.AutoCloseOutputStream .

If I use:
            // Write the file
                    FileOutputStream fos = new FileOutputStream(new File(getFilesDir(), "out.txt"));
            OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fos);

it WORKS correctly on any API level.

But as I am using external storage and have to use the ContentProvider given when I get access to the storage via a chooser, all I have to deal with is a content Uri and not a file name nor file handle.  I have to go through the getContentResolver methods.

Note that:

            // Write the file
                    ParcelFileDescriptor pfd = getContentResolver().openFileDescriptor(currentUri, "w");
                    FileDescriptor fd = pfd.getFileDescriptor();
                    FileOutputStream fos = new FileOutputStream(fd);
            OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fos);

Does not work either.  Somewhere in the ParcelFile system things are going wrong.