Parsing JSON in Java with variable number of objects

Question

My app receives a JSON response from web services and processes the data. The response that is received could have any number of objects. My normal method of parsing is:

JSONObject jsonObj = new JSONObject(json);
JSONArray arrChanges = jsonObj.getJSONObject("Changes").getJSONArray("Row");
for (int i = 0; i < arrChanges.length(); i++)
{
    // do stuff
}

This normally gets the array Row inside the object Changes, and works fine. However, I tested it with only one record being returned, and suddenly got the error: JSONObject cannot be converted to JSONArray. After looking at the json, I can see that because there is now only one object, it is no longer a JSONArray, it is now just a JSONObject. Meaning that trying to use getJSONArray will obviously fail.

So my question is; considering I will receive a varying number of items (0 to lots), how can I reliably parse this data (without knowing how many records it will have)?

I'll suggest you you use Gson library. Simply create a modal class then you can always check length of array. Or use condition if(jsonObj.getJSONObject("Changes").getJSONArray("Row")!=null) or if(! jsonObj.getJSONObject("Changes").getJSONArray("Row").isEmpty()) — Kaustuv, May 19 '14 at 15:51
you always know the size of json array so your by this code arrChanges.length(). I think you are using php on your server side and if you json encode empty array it is converted to json array in php — Illegal Argument, May 19 '14 at 15:51

score 0 · Answer 1 · answered May 19 '14 at 16:01

0

Force your json to be an array on the client side.

EDIT: I said client, I just mean wherever you are creating it.

var json = [];

json.push({"yourdataname":"yourdatavalue"});

answered May 19 '14 at 16:01

user3608828

52
6

I'd agree that the data should be forced to be an array when the json is created, even if the array only contains one item, you need some structure. – darnmason May 19 '14 at 16:06
This is my ideal solution but I'm afraid I don't really understand how this code converts a JSONObject to a JSONArray. – Mike Baxter May 22 '14 at 11:24
Your array needs to an array, weather it has 1 item or 1000, not an n sized collection of objects. force it to be like {"Row":[{},{}]} I hope that helps. I'm not an expert, but I had a similar issue once. – user3608828 May 22 '14 at 21:22

score 0 · Accepted Answer · answered May 19 '14 at 16:04

Try editing parsing with the help of this concept

if (<your jsonobject> instanceof JSONArray)
 {
  //parse as an jsonarray
  for(....;....;...){
 //your logic
 }
 }
 else{
 //parse as jsonobject without using any index value
 }

hope this help you with your problem.

score 0 · Answer 3 · answered May 19 '14 at 16:12

Just another way to do it:

try{
JSONArray arrChanges = jsonObj.getJSONObject("Changes").getJSONArray("Row");
for (int i = 0; i < arrChanges.length(); i++)
{
    // do stuff
}
}catch(JSONException e){
//i assume that the actual data is json array if not this block is called try jsonobject parsing here 
// its something like try catch inside try catch
}

Parsing JSON in Java with variable number of objects

3 Answers3