Parsing JSON Array within JSON Object
mainJSON.getJSONArray("source") returns a JSONArray, hence you can remove the new JSONArray.
The JSONArray contructor with an object parameter expects it to be a Collection or Array (not JSONArray)
Try this:
JSONArray jsonMainArr = mainJSON.getJSONArray("source");
Your code is fine, just replace the following line:
JSONArray jsonMainArr = new JSONArray(mainJSON.getJSONArray("source"));
with this line:
JSONArray jsonMainArr = mainJSON.getJSONArray("source");