Re-wrote Java App in Flutter, Can't Access Previous Internal Storage

I first wrote my app in Java a while ago, and I used the app's internal storage for saving lists of players and some DLC. The structure on an Android device looked like:

ca.bigbeanbag.myapp / files / backup / playerbackup.xml

I have now completely rewritten the app in Flutter (so I can also release on iOS), and I would like to be able to migrate the player backup from the java version. It seems that flutter uses a different starting point for internal storage (it adds folder app_flutter first). On a device that was upgraded from the java version to the flutter version, the tree looks like:

ca.bigbeanbag.myapp /
.. app_flutter/files/backup      <-- new flutter storage location
.. files/backup                  <-- old java storage location

So on first run of the new flutter version of the app, I just use the parent to find my way to the java-version files, and import them over to the new flutter storage location

    var docsDir = await getApplicationDocumentsDirectory();
    String oldBackupPath = docsDir.parent.path + '/files/backup/backup.xml';
    String destinationPath = docsDir.path + '/files/backup/';

... and copy

In debug mode on the emulators, this works great.

However on a real device, when I get a directory listing of the old java folders (ca.bigbeanbag.myapp/files) instead of what I get when on emulator/debug mode:

ca.bigbeanbag.myapp/files/
.. backup
.. dlc_stuff

I get this instead:

ca.bigbeanbag.myapp/files/
.. rList
.. generatefid.lock
.. PersistedInstallation.W0RFRkFVTFRd+(lots of letters).json

So in reelase on a real device I can't access the internal storage of the older java version.

I have used the same package name as the previous java version
I have used the same signing keys
I released the new flutter version as an internal test on the java version Google Play Store

I'm not sure what else to do at the point. Hoping someone will have some ideas / guidance.

Solution

I never found out exactly why I wasn't getting access to the java internal storage area from the new flutter/dart version, but I did discover it has something to do with using a relative reference.

In the flutter version the internal storage is stored under 'app_flutter', and hopping up to the parent and down to the java-app created folder like this:

   var docsDir = await getApplicationDocumentsDirectory(); 
   // docsDir now equals "../ca.bigbeanbag.net.myapp/app_flutter/"
    String oldBackupPath = docsDir.parent.path + '/javafiles/backup.xml';

doesn't work. However if I reference the java-app created folder all the way from the top:

/sdcard/Android/data/... .../ca.bigbeanbag.myapp/javafiles/

it worked ok and I was able to read javafiles.

Hope this helps anyone else. Thanks to anyone that read the question.