Nifi JOLT accessing a JSON value,NiFi expression language within JOLT

[#1]

Hi There,

I wish to apply a simple transformaton to a JSON using JOLT. I want to apply :substring(1,2) to the value of the key. I am using default jolt transformation but I don't know how to access the value of JSON from within JOLT and then apply the transformation?

Please help.

JOLT :

[{
"operation": "default",
"spec": {
      "c":"${b:substring(1,2)}"
}
}] 

JSON :

{
  "b":"hello"
}

Result :

{
  "c":"",
  "b":"hello"
}

Expected result :

{
  "c":"e",
  "b":"hello"
}

[#2 · Accepted solution]

@John Smith

Extract the b attribute value before using it in Jolt transform by using EvaluateJson path processor and keep destination as flowfile-attibute.Then add your b attribute as a new property in evaluatejson path processor once we add b attribute to the flowfile then your jolt transform will apply substring function on the b attribute.

EvaluateJsonPath configs:-

Example:-

for testing i have added b attribute value as default in my jolt transform

Jolt spec testing:-

As you can see at right below corner we are having output json content with c key having e as value.

Let us know if you are having issues/questions..!!