I've playing around with Google App Engine and Google Datastore for a while now and I am facing the need to take regular backups of my stuff up on the cloud.
Is there any sort of general purpose tool that allows you to download all your data from a specific instance of google-datastore and restore it to another one?
If so, please enlighten me, if not - someone should do it!
There is an opensource application available that I developed called "GAE datastore backup utility." It allows you to backup and restore your GAE entities through a GUI. It keeps track of your applications and your application's entities. It's currently only for Windows and Python based GAE apps but it sounds like something you are looking for. I see that you are looking for a solution for Java based apps. I will look into supporting this language in the next release.
You may have a look at the following site: http://aralbalkan.com/1837
It is about the backup and restore of the datastore.
I describe bulkloader.py no-config dump/restore in What's the best way to back up data on Google App Engine?
After years, this came out as a feature of the Datastore Administration in the app-engine dashboard, still experimental but still good news!