Note: The underlying JsonPath library loads the entirety of the streamed content into and performs result evaluations in memory. Accordingly, it is important to consider the anticipated profile of content being evaluated by this processor and the hardware supporting it especially when working against large JSON documents.
It's a common pattern to make JSON from attributes in NiFi. Many of these attributes have periods in their names. For example record.count. To reference them safely, you must use this sort of operation which puts the entire key in brackets. This also applies to JSON keys that contain whitespace:
$.["record.count"]
$.["record count"]