Question

I haven’t found any documentation on flash.discard(). What does it do?

Answer 1

After looking at the code, this is what I understand:

1. The Flash data is ultimately for storing data between requests.
2. Since Play is stateless, that state is saved in a session cookie, which is send to the client and send back with the next request.
3. The data Map is the data that comes from the client via the cookie.
4. The out Map is the data that the Play app writes to the Flash instance.
5. If the data changed, the data in the out Map is used to build the content of the cookie to send back to the client.

So from this, I would say, that flash.discard() is used to throw away everything that would go to the client, and flash.clear() is used to throw away everything that came from the client…