Cloudera Docs

Expression Language Hierarchy

When using Expression Language to reference a property by name there is a defined hierarchy within which NiFi will search for the value.

The current hierarchy in NiFi is as follows:

  1. Search FlowFile for attribute/key

  2. Search Process Group Variables for attribute/key

  3. Search File Registry file for attribute/key

  4. Search NiFi JVM Properties for attribute/key

  5. Search System Environment Variables for attribute/key

NiFi will search for, and return, the first occurrence of a matching property. If no matching property is found, null is returned.