What I want to do seems simple, but all of the info I'm finding looks like overkill.
I have a message with a Hash for payload. It can have any number of fields.
All I want to do is make 1 additional entry in the hash.
(I'm trying to copy one hash entry to another name via MEL. I'd even be happy to rename the entry. Actually all I'm really trying to do is change the case of key from "Foobar" to "foobar")
The "Set Payload" replaces the entire payload, not what I want.
The "Message Enricher" wants to call other processors, etc, not what I need.
"Data Mapper" was the other item I looked at, it looks like you can go from Map -> Map, but I don't understand how to tell it "copy this 1 field (or rename it), but leave everything else as-is."