how to check if a JSONArray is empty in java? - arrays

Question

I am working on an android app that get json content of a webservice called "WebUntis". The Json content i am getting looks like:
{"jsonrpc":"2.0","id":"req-002",
"result":[
{"id":125043,"date":20110117,"startTime":800,"endTime":850,
"kl":[{"id":71}],
"te":[{"id":23}],
"su":[{"id":13}],
"ro":[{"id":1}]},
{"id":125127,"date":20110117,"startTime":1055,"endTime":1145,
"kl":[{"id":71}],
"te":[{"id":41}],
"su":[{"id":19}],
"ro":[{"id":31}]},
...]}
As you can see in the result-array there are also other arrays like "kl", "su" and "ro"
I am getting the content of these array and then i store them in an arraylist.
But when one of these array is empty, like;
{"jsonrpc":"2.0","id":"req-002",
"result":[
{"id":125043,"date":20110117,"startTime":800,"endTime":850,
"**kl":[]**,
"te":[{"id":23}],
"su":[{"id":13}],
"ro":[{"id":1}]},
{"id":125127,"date":20110117,"startTime":1055,"endTime":1145,
"kl":[{"id":71}],
"te":[{"id":41}],
"su":[{"id":19}],
"ro":[{"id":31}]},
...]}
I am always getting the error IndexOutOfRangeException,
but I am always telling it that it should not take the empty arrays, this is what I have tried:
JSONObject jsonResult = new JSONObject(s);
// Get the result object
JSONArray arr = jsonResult.getJSONArray("result");
for (int i = 0; i < arr.length(); i++) {
JSONObject c = arr.getJSONObject(i);
anfangStunde[i] = c.getString("startTime");
endeStunde[i] = c.getString("endTime");
// get the jsonarrays (kl, su, ro)
kl = c.getJSONArray("kl");
su = c.getJSONArray("su");
ro = c.getJSONArray("ro");
// check if kl is not null
if(kl != null){
klassenID[i] = kl.getJSONObject(0).getString("id");
}
if (klassenID[i] != null) {
klasse = webuntis.klassenMap.get(klassenID[i]);
Log.d("ID und Klasse=", "" + klassenID[i] + ";" + klasse);
}
// get th ids
fachID[i] = su.getJSONObject(0).getString("id");
if (fachID[i] != null) {
fach = webuntis.faecherMap.get(fachID[i]);
Log.d("ID und Fach=", "" + fachID[i] + ";" + fach);
}
// "Start;Ende;Klasse;Fach;Raum" store in arraylist
webuntis.stundenPlan.add(anfangStunde[i] + ";" + endeStunde[i] + ";" + klasse + ";" + fach);
// Write Data into a file for offline use:
}
Can anyone help me ?

Answer 1

If the array is defined in the file but is empty, like:
...
"kl":[]
...
Then getJSONArray("kl") will return an empty array, but the object is not null. Then, if you do this:
kl = c.getJSONArray("kl");
if(kl != null){
klassenID[i] = kl.getJSONObject(0).getString("id");
}
kl is not null and kl.getJSONObject(0) will throw an exception - there is no first element in the array.
Instead you can check the length(), e.g.:
kl = c.getJSONArray("kl");
if(kl != null && kl.length() > 0 ){
klassenID[i] = kl.getJSONObject(0).getString("id");
}

Answer 2

You can also use isEmpty() method, this is the method we use to check whether the list is empty or not. This method returns a Boolean value. It returns true if the list is empty otherwise it gives false. For example:
if (!k1.isEmpty()) {
klassenID[i] = kl.getJSONObject(0).getString("id");
}

Answer 3

You can use the regular length() method. It returns the size of JSONArray. If the array is empty, it will return 0. So, You can check whether it has elements or not. This also keeps you in track of total elements in the Array, You wont go out of Index.
if(k1 != null && k1.length != 0){
//Do something.
}

Answer 4

This is another way to do it...
call.enqueue(new Callback<JsonObject>() {
#Override
public void onResponse(Call<JsonObject> call,
Response<JsonObject> response) {
JSONObject jsonObject;
try {
jsonObject = new JSONObject(new Gson().toJson(response.body()));
JSONArray returnArray = jsonObject.getJSONArray("my_array");
// Do Work Only If Not Null
if (!returnArray.isNull(0)) {
for (int l = 0; l < returnArray.length(); l++) {
if (returnArray.length() > 0) {
// Get The Json Object
JSONObject returnJSONObject = returnArray.getJSONObject(l);
// Get Details
String imageUrl = returnJSONObject.optString("image");
}
}
}
} catch (JSONException e) {
e.printStackTrace();
}
}
#Override
public void onFailure(Call<JsonObject> call,
Throwable t) {
}
});