Error when posting JSON using NiFi vs. curl - json

Question

I am seeing a very slight difference between how NiFi's InvokeHTTP processor POSTs json data and how curl does it.
The problem is that the data APPEARS to be the same when I log it ... but the data is rendering differently.
Does anyone have any idea what could be wrong? Thank you!
CURL -- works; correct printout & render
curl -X POST -H "Content-Type: application/json" -d '{ "responseID": "a1b2c3", "responseData": { "signals": [ "a", "b", "c" ] } } localhost:8998/userInput
WebServer app printout
responseID: a1b2c3
responseData: {signals=[a, b, c]}
Template render
NiFi -- does not work; correct printout BUT incorrect render
Generate FlowFile
UpdateAttributes
AttributesToJSON
InvokeHTTP
WebServer app printout
responseID: a1b2c3
responseData: {signals=[a, b, c]}
Template render

Answer 1

you need this kind of json:
{ "responseID": "a1b2c3", "responseData": { "signals": [ "a", "b", "c" ] } }
but in nifi you building this:
{ "responseID": "a1b2c3", "responseData": "{ signals=[ a, b, c ] }" }
it means that you create responseData just as a string "{ signals=[ a, b, c ] }" but you need an object
in nifi the AttributesToJSON processor creates only one level object, so you can create a sequence of AttributesToJSON -> EvaluateJsonPath -> AttributesToJSON to make nested json objects.
or use ExecuteStript with javascript or groovy language - both has good syntax to build json.