Download file from Dropbox to local android Java

In general, to download a file, you need to open it and hold it open while waiting for the download to complete. (Everything in the Sync SDK is asynchronous.)

So the usual pattern here is to open the file, register a listener on that file, wait for getNewerStatus().isCached to be true, and then call update() on the file. At that point, you should be able to read the latest file contents. (If you read before that, you'll either see cached data if available or you'll perhaps hang the UI thread waiting for network I/O.)

I would actually expect your original code to work (but hang the thread), since getReadStream() should block if there's no cached data.

Can you confirm that after dst.transferFrom(src, 0, src.size());, the file is empty (or there is some other problem with it) to narrow down the issue?