WSO2, XML to JSON, force a single element to be treated as array

In Enterprise Integrator 6.6.0 I'm converting a XML to JSON payload.

If the XML source has a single element it gets obviously treated as a single object

<items>
 <item></item>
</items>

becomes

{
    "items": {
        "item": {}
    }
}

but if there are more element, the specific object is treated as an array

<items>
 <item></item>
 <item></item>
</items>

becomes

{
    "items": {
        "item": [{}, {}]
    }
}

Is there a way to align the conversion of a specific sub-object? In this case, I'm trying to always return an item array, even when there is only a single element.

I read about the xml-multiple property but I couldn't understand how to use it; is it to be set manually to the source xml payload?

Solution

You can use the Json transform mediator[1] to achieve your use-case. Here we need to define the json schema to match the expected data structure. For the above case you will be able to use a json schema similar to the following.

 {
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "properties": {
    "items": {
      "type": "object",
      "properties": {
        "item": {
          "type": "array",
          "items": [
            {
              "type": "object"
            }
          ]
        }
      },
      "required": [
        "item"
      ]
    }
  },
  "required": [
    "items"
  ]
}

This specifies that the item is an array. Then the schema can be added to the registry [2] and referred in the json transform mediator. The Json transform mediator needs to be added after the xml to json transformation. Refer to the following sample proxy service.

<?xml version="1.0" encoding="UTF-8"?>
<proxy xmlns="http://ws.apache.org/ns/synapse"
       name="transform"
       startOnLoad="true"
       statistics="disable"
       trace="disable"
       transports="http,https">
   <target>
      <inSequence>
         <property name="messageType" scope="axis2" value="application/json"/>
         <property name="ContentType" scope="axis2" value="application/json"/>
         <jsontransform schema="conf:/schema.json"/>
         <respond/>
      </inSequence>
   </target>
   <description/>
</proxy>

input 1

<items>
 <item><val1></val1></item>
 <item><val1></val1></item>
</items>

output 1

{
    "items": {
        "item": [
            {
                "val1": null
            },
            {
                "val1": null
            }
        ]
    }
}

input 2

<items>
 <item><val1></val1></item>
</items>

output 2

{
    "items": {
        "item": [
            {
                "val1": null
            }
        ]
    }
}

[1]-https://docs.wso2.com/display/EI660/JSON+Transform+Mediator

[2]-https://docs.wso2.com/display/EI660/Managing+the+Registry+