Though this question may relate to Hadoop-Common project but, I faced the concern while working with MR.
The current version of Hadoop deprecates many keys but, takes care of adding the new keys to the configuration accordingly.
For the end user only logs are there which indicates the key is deprecated and the message also suggests the new key to be used.
I was thinking; there should be an API/Utility which could probably provide the new key information when called with old key.
Using this API the user can judge in runtime to use the old key or new key.
Currently the Configuration provides an API only to check whether a key is deprecated or not but, doesn't provides a way to get the corresponding new key.