Android: Move large number of files to SD card transactionally?

Question

Lets say I have a database with a few hundred blobs stored in separate files I want to move to the SD card, what is the best way of programatically doing this ensuring nothing gets left behind?

I realize I can only copy files across different mounts.

So can I copy all the files to a subdirectory in "cache" and then move the subdirectory to the correct spot atomically? Or can I write all to the files to a directory with a "temp" prefix, and rename it in place when verified?

Answer 1

The possibility to move the folder (I mean, relocate it just by renaming) depends on the file system and probably it is better not to rely on in. Also, even when it works, it only works inside the boundaries on the single mount. I would propose simply to rename the folder after all files have been successfully copied.

If the folder with "temporary" prefix would be discovered due previous crash, it can be simply removed ("rollback").

Answer 2

I would recommend finding a library with an algorithm that is designed for problems such as this. You might want to start by reviewing this question Any good rsync library for Java?