Is there another way / proper way of parsing this JSON array ?

I have a JSON object which holds some json_array like this: (with org.codehaus.jettison.json.*)

json array:[{"C1":["S1","S2"]},{"C2":["S1","S2"]},{"C3":["S1","S2"]},{"C4":["S1","S2"]}]

I have to get two list,one for keys,another for the elements of each key.I have done like this:

//sample: clusterIdList:[C1, C2, C3, C4] and serviceIdList:[S1, S2, S1, S2, S1, S2, S1, S2]

    //get jsonarray by key = serviceCode
    JSONArray array = incident.getJSONArray("serviceCode");


    List<String> clusterIdList = new ArrayList<String>();
    List<String> serviceIdList = new ArrayList<String>();
    String key="";

    for (int i = 0,length=array.length(); i < length; i++) {
        JSONObject b = array.getJSONObject(i);
        key = b.names().getString(0);
        clusterIdList.add(key);
        JSONArray sublist = b.getJSONArray(key);
        for (int j = 0,sublistLength = sublist.length(); j < sublistLength; j++) {
            serviceIdList.add(sublist.getString(j));
        }
    }

Is this a proper way to do this? or can it be improved? I am trying to improve my code quality and readability.