Converting xml input into json format with skipping parent keys but coping its values to childs

Question

I must convert XML document to JSON format with skipping specified keys and appending its values to parents. I'm forced to use Java 7. For example I have following XML and I must skip "message" elements:

<messages>
 <message>1</message>
 <message>2</message>
 <message>3</message>
 <message>4</message>
</messages>

Expected output is:

{
"messages" : [
  1,
  2,
  3,
  4
 ]
}

I'm using XML.toJSONObject(xmlInput) from org.json library to convert xml to jsonObject. Then I tried to convert jsonObject to expected output in two ways:

a) by using jsonPointer - I failed because I did not have access to parent element

b) by manipulating resulted json with regular expressions - I failed because it seemed very complicated

Do you have any idea how to do it?