Apache Nifi PutFTP change extension of file

Use an UpdateAttribute processor to change the filename attribute of the flowfile from example.csv to example.json.

A more dynamic answer when using UpdateAttribute is to use NiFi expressions to change the filename:

So to change dynamc_name.txt to dynamc_name.json

Set your NiFi UpdateAttribute filename to:

${filename:substring(0,11).json} 

Expression                                              Value

${filename:substring(0,1)}                              a

${filename:substring(2)}                                brand new filename.txt

${filename:substring(12)}                               filename.txt

${filename:substring( ${filename:length():minus(2)} )}  xt

Reference: https://docs.cloudera.com/HDPDocuments/HDF3/HDF-3.0.2/bk_expression-language/content/substring.html

I agree that the UpdateAttribute worked well but struggled to find an expression that worked with it. After some testing and research I arrived at this solution.

${filename:substringBeforeLast('.'):append('.json')}