Using flowfile size as an argument in RouteOnAttribute nifi

Question

I want to know if is it possible to use flowfile size as an argument in routeOnAttribute i want to make expression like that :

${filename.fileSize>500}

but it tells me that expression ought to return true and my expression returns string what should i do to be able to make new connection in routeOnAttribute(p.s filename is my flowfile name)

EDIT 05/17/2019 Correct answer is Andy's. That is the best guidance from us (Apache NiFi team) on the subject. The answer marked "correct" only applies in a few cases where Content-Length is set by an upstream processor. Andy's solution, fileSize is universally applicable.

Answer 1

Your expression is logically correct but does not use valid Apache NiFi syntax. It should use the gt function as below:

${fileSize:gt(500)}

This will return a boolean result.

Answer 2

On the RouteOnAttribute, you can configure an attribute whose value evaluates to true when flowfile content is of certain size.