parsing Json in Android Studio when result is empty - json

Question

I try to load datas from a Json that is on my server to my smartphone.
When the json is like this, it works and i get the label "spanishguitar":
{"file": "image.jpg", "objects": [{"bbox": [611, 82, 1231, 1265], "label": "spanishguitar", "prob": 0.991}]}
Here is my code:
public void updateLabel() {
try {
HttpClient client = new DefaultHttpClient(getHttpRequestParams());
HttpGet getJson = new HttpGet(SERVER_ADRESS + "objects.json");
HttpResponse jsonResponse = client.execute(getJson);
if (200 == jsonResponse.getStatusLine().getStatusCode()) {
InputStream inputStream = jsonResponse.getEntity().getContent();
String json = IOUtils.toString(inputStream);
JsonResult jsonResult = new Gson().fromJson(json, JsonResult.class);
instrumentname = jsonResult.objects.get(0).label;
But sometimes the json is empty like this:
{"file": "image.jpg", "objects": []}
So my plan is that if objects == null to get something like:
Toast.makeText(getApplicationContext(), "Uuuups, itś empty", Toast.LENGTH_SHORT).show();
Do you know how to parse the json, so that i get a message in the case of an empty "objects"?
Thank you!
Now it works. Here is my code:
#RequiresApi(api = Build.VERSION_CODES.N)
private void empty() throws IOException {
try {
HttpClient client = new DefaultHttpClient(getHttpRequestParams());
HttpGet getJson = new HttpGet(SERVER_ADRESS + "objects.json");
HttpResponse jsonResponse = client.execute(getJson);
InputStream inputStream = jsonResponse.getEntity().getContent();
String json = IOUtils.toString(inputStream);
JsonParser parser = new JsonParser();
JsonElement element = parser.parse(String.valueOf(json));
JsonObject obj = element.getAsJsonObject();
JsonArray objects = obj.getAsJsonArray("objects");
if (objects == null || objects.size() == 0) {
/////////////
runOnUiThread(new Runnable() {
#Override
public void run() {
noResult.setVisibility(View.VISIBLE);
Toast.makeText(getApplicationContext(), "Identification failed", Toast.LENGTH_SHORT).show();
}});
progressBar.setIndeterminate(false);
progressBar.setVisibility(View.INVISIBLE);
} else {
updateLabel();
}
} catch (IOException e) {
e.printStackTrace();
} catch (UnsupportedOperationException e) {
e.printStackTrace();
} catch (JsonSyntaxException e) {
e.printStackTrace();
}
}
Thank you a lot for your help!

Answer 1

'Empty' is not 'null'.You can use
ArrayUtils.isEmpty(objects)
or
objects == null || objects.length() == 0
to detect whether you got an empty objects.
I writed a demo for you:
import com.google.gson.*;
public class Main
{
public static void main(String[] args)
{
JsonParser parser = new JsonParser();
// JsonElement element= parser.parse("{\"file\": \"image.jpg\", \"objects\": []}");
JsonElement element= parser.parse("{\"file\": \"image.jpg\", \"objects\": [{\"bbox\": [611, 82, 1231, 1265], \"label\": \"spanishguitar\", \"prob\": 0.991}]}");
JsonObject obj = element.getAsJsonObject();
JsonArray objects = obj.getAsJsonArray("objects");
if(objects == null || objects.size() == 0) {
System.out.println("objects is empty");
}else{
JsonObject firstObj = objects.get(0).getAsJsonObject();
System.out.println("objects[0].label="+firstObj.get("label"));
}
}
}