I've done something similar in e42f4f77000a160f4eafef2cc5d2f954108df897. I created a `splitContainerAndKey` method so I could unit test it to check it worked. I used the name `splitContainerAndKey` instead of `splitContainerAndPrefix` because 'key' is more general than 'prefix' and this method is potentially reusable. I then explicitly did `String prefix = parts[1]` to try to make it clear that I was deliberately treating the 'key' part of the string as a prefix.