Decode json returns null in Java

Question

I have the following JSONArray:

[
   {
      "Lng":17.908817,
      "name":"S1",
      "id":1,
      "sensor:":[
         "Temperature",
         "Wind"
      ],
      "Lat":47.089492
   },
   {
      "Lng":17.908458,
      "name":"S2",
      "id":2,
      "sensor:":[
         "Temperature",
         "Wind",
         "Humidity"
      ],
      "Lat":47.089246
   },
   {
      "Lng":17.908222,
      "name":"S3",
      "id":3,
      "sensor:":[
         "Wind"
      ],
      "Lat":47.089662
   }
]

I can split it to JSONObject but if I try to split the Object it returns null.

My code:

    Object object = JSONValue.parse(result);
    JSONArray array = (JSONArray)object;
    for(int i = 0 ; i < array.size(); i++){
        System.out.println(array.get(i));

        JSONObject jsonObject = (JSONObject)array.get(i);

        for(int j = 0 ; j < jsonObject.size(); j++){
            System.out.println(jsonObject.get(j));

        }

    }

Result:

{"Lng":17.908817,"name":"S1","sensor:":["Temperature","Wind"],"id":1,"Lat":47.089492}
null
null
null
null
null
{"Lng":17.908458,"name":"S2","sensor:":["Temperature","Wind","Humidity"],"id":2,"Lat":47.089246}
null
null
null
null
null
{"Lng":17.908222,"name":"S3","sensor:":["Wind"],"id":3,"Lat":47.089662}
null
null
null
null
null

Sotirios Delimanolis · Accepted Answer · 2014-08-27 15:45:42Z

3

A JSONObject (a JSON object) is not indexable. Elements are unordered. What you are trying to do

System.out.println(jsonObject.get(j));

doesn't make sense. Access name-value pairs through their names.

answered Aug 27, 2014 at 15:45

Sotirios Delimanolis

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6 Comments

Sotirios Delimanolis Over a year ago

@user3768431 The array has the name sensor, so you can access it with jsonObject.get("sensor").

Duncan Over a year ago

I realized after i post the question.

Duncan Over a year ago

One more and I let it. What is the proper way? I tried this: JSONArray array2 = (JSONArray)jsonObject.get("sensor"); but it isnt working.

Sotirios Delimanolis Over a year ago

@user Which library are you using? I might have gotten them wrong. Also, what does is not working mean? Does it throw an exception? Does it return null?

Sotirios Delimanolis Over a year ago

@us Oh, there's a : at the end of sensor.

|

ROMANIA_engineer · Accepted Answer · 2014-08-27 15:48:54Z

0

You can use:

Iterator<?> keys = jsonObject.keys();

while( keys.hasNext() ){
    String key = (String)keys.next();
    // use jsonObject.get(key)
}

instead of that "j".

answered Aug 27, 2014 at 15:48

ROMANIA_engineer

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Comments

tmarwen · Accepted Answer · 2014-08-27 15:58:27Z

0

Try to access the JSONObject properties through their keys:

JSONArray array = JSONValue.parse(result);
for(int i = 0 ; i < array.size(); i++) 
{
  System.out.println(array.get(i));
  JSONObject jsonObject = (JSONObject) array.get(i);
  int id = jsonObject.getInt("id");
  String lng = jsonObject.getString("Lng");
  String lat = jsonObject.getString("Lat");
  Object sensor = jsonObject.getString("sensor");
  String name = jsonObject.getString("name");
  System.out.println(id);
  System.out.println(name);
  System.out.println(sensor);
  System.out.println(lat);
  System.out.println(lon);
}

answered Aug 27, 2014 at 15:58

tmarwen

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