Execute Groovy Script to transform date in Nifi - groovy

Question

I'm trying to transform my JSON dates using Nifi. They are imported in this format:
import groovy.json.JsonSlurper
import groovy.json.JsonBuilder
def ff = session.get()
if(!ff)return
ff = session.write(ff, {rawIn, rawOut->
// transform streams into reader and writer
rawIn.withReader("UTF-8"){reader->
rawOut.withWriter("UTF-8"){writer->
//parse reader into Map
def json = new JsonSlurper().parse(reader)
// set my variable and define what format it is in
json.date = new Date(json.date as Long).format('HH:mm yyyy-MM-dd')
// Reformat it
json.date = DateFormat.parse("yyyy-MM-dd HH:mm", json.date)
//write changed object to writer
new JsonBuilder(json).writeTo(writer)
}
}
} as StreamCallback)
session.transfer(ff, REL_SUCCESS)
The incoming flowfile has this body:
[{"date":"09:00 2019-05-29","data":460.0,"name":"login"},{"date":"10:00 2019-05-29","data":548.0,"name":"login"},{"date":"11:00 2019-05-14","data":0.0,"name":"login"},{"date":"00:00 2019-06-15","data":0.0,"name":"login"}]
I want this output:
[{"date":"2019-05-29 09:00","data":460.0,"name":"login"},{"date":"2019-05-29 10:00","data":548.0,"name":"login"},{"date":"2019-05-14 11:00","data":0.0,"name":"login"},{"date":"2019-06-15 00:00","data":0.0,"name":"login"}]
The error I get is this:
Can anyone please help me understand where I am going wrong?

Answer 1

The input is a list of the objects in question. The incoming date is a
String -- not a Long.
So the first error is to use json.date as it implies json*.date
(which gives a list of all date).
Next casting the date to Long, create a new Date and then format it is
the wrong way around.
So to change the format of all the date something like this is needed:
json.each{
it.date = Date.parse('HH:mm yyyy-MM-dd', it.date).format('yyyy-MM-dd HH:mm')
}