This document discusses how to transform a JSON payload into a different JSON format in Mule. It provides an example of transforming an input JSON with name and id fields into an output JSON that adds a designation field. The document recommends using an expression transformer to dynamically modify the JSON and outputs a sample Mule flow that demonstrates transforming one JSON payload into another JSON payload with an added field using an expression transformer.

1. JSON to JSON transformation in Mule

2. We often deals with JSON payloads in our
application on a large scale, specially whenever
we are exposing or consuming a REST API. One of
the common scenario we get is to modify or
transform the input JSON payload to another JSON
format and produce it as an output.

3. if we consider the following
{
"name": “Maurizio Rorato",
"id": 37
}
This is a simple JSON payload taken as an example,
which contains only 2 elements, that
is name and id.

4. So, if this JSON payload is coming into our
application as an input and we require to
transform/modify the payload into another JSON format
and produce it as an output, something like the following
{
"name": "John Rosso",
"id": 37,
"designation": "Director"
}

5. Where you can see the modified JSON has a new
element designation as a third element. The challenge here
is to modify the existing input JSON payload and
to design an output JSON payload from it, which will
contain this additional element in it with the same format.
So, the question is, how can be the input JSON format can
be modified or transformed in another JSON format that we
require, in a Mule application ??

6. The answer is Mule has a rich set of transformers and offers
different options to transform form one format of payload
into another. Mule also offers a powerful component
called Datamapper, which is limited to Mule enterprise
edition, and that can perform all these requirement in easy
way.

7. But here for Mule community edition, we will choose a
simplest way of doing it. We will be using Expression
Transformer for doing this.
Here is the following Mule flow, where we can
transform the JSON input into another JSON format.
So, you can transform from one JSON to another
dynamically using Expression transformer in the
following flow.

8. <flow name="DynamicJSONFlow1" doc:name="DynamicJSONFlow1">
<http:inbound-endpoint exchange-pattern="request-response" host="localhost"
port="8085" path="test" doc:name="HTTP"/>
<json:json-to-object-transformer returnClass="java.lang.Object" doc:name="JSON
to Object"/>
<set-variable variableName="name" value="#[message.payload.name]"
doc:name="Variable"/>
<set-variable variableName="id" value="#[message.payload.id]"
doc:name="Variable"/>
<expression-transformer

9. expression="#[[
'name':flowVars.name,
'id':flowVars.id,
'designation':'Designation'
]
]" doc:name="Expression"/>
<json:object-to-json-transformer doc:name="Object to JSON"/>
<logger level="INFO" message="#[message.payload]"
doc:name="Logger"/>
</flow>