seriously seriously - 3 months ago 14
JSON Question

how to check if a JSONArray is empty in java?

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

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 test the length(), e.g.:

kl = c.getJSONArray("kl");
if(kl != null && kl.length() > 0 ){
   klassenID[i] = kl.getJSONObject(0).getString("id");
}
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