How to load the entire directory folder into the Dropbox API?

How to upload an entire image folder (in a specific directory) to Dropbox using the Dropbox API?

In the sample code, it loads a specific file with the same file name, however, I saved the image file names according to the time at which it was taken, and therefore I could not load the saved file.

I tried using:

File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM);
String imageFileName = "Pictures" + date.toString()+ ".jpg";
File file = new File(path+File.separator, imageFileName);

But when trying to download the file was not found.