org.json.JSONException: JSONObject["alias"] not a string

Question

I'm trying to get the alias string from the json file.But I'm getting the exception saying alias is not a string. org.json.JSONException: JSONObject["alias"] not a string.

String qsCurrentLine;
    try {
        brq = new BufferedReader(new FileReader("/home/storm/Videos/2.json"));
        try {
            while ((qsCurrentLine = brq.readLine()) != null) {
                //System.out.println(qsCurrentLine);
                //reads the line makes it json object
                JSONObject question=new JSONObject(qsCurrentLine);
                //System.out.println(question);
                JSONArray usersarray=question.getJSONArray("users");
                //System.out.println(usersarray);
                for(int i=0;i<usersarray.length();i++){
                JSONObject questions=usersarray.getJSONObject(i);
                //System.out.println(questions);
                int qus=questions.getInt("id");
                //System.out.println(qus);
                //String alias=questions.getString("alias");
            //String check=questions.getString("answer");
            //System.out.println(check);
            String check1=questions.getString("question");
            //System.out.println(check1);
            String check2=questions.getString("_subtype");
            //System.out.println(check2);
            String check3=questions.getString("_type");
            //System.out.println(check3);
            String check4=questions.getString("options");
            //System.out.println(check4);

                System.out.println("HELLO    "+questions.getString("alias"));

        //  System.out.println(check5);

            int check6=questions.getInt("id");
            System.out.println(check6);

                //System.out.println("This alias " +aliass);

                }
                //JSONObject data25=array.getJSONObject(25);
                //System.out.println(data25);
                //question1060=data25.getString("question_36__option_10160_");
                //System.out.println("the question number of 1060: "+question1060);
            }
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

I'm getting all other String values but when I try to get the alias String I'm getting the exception I don't understand why?

Here this the sample of my json file.

{"answer":null,"question":"<h1 style=font-family:Lato, sans-serif;font-weight:600;font-size:28px;>   Your response to our survey will help us identify how we are serving the needs of different companies.<\/span><\/span>","_subtype":"instructions","_type":"SurveyDecorative","options":"[]","alias":null,"id":73}

even if alias is NULL it should get the null string can any of you explain this why it is happening like this.

Thanks in Advance

Answer 1

What is the problem

org.json.JSONObject#getString(String) throws JSONException if property for key exists, but is null.

Why does it happen

See code http://grepcode.com/file/repo1.maven.org/maven2/org.json/json/20080701/org/json/JSONObject.java

public String getString(String key) throws JSONException {
   return get(key).toString();
}

where get is

 public Object get(String key) throws JSONException {
     Object o = opt(key);
     if (o == null) {
         throw new JSONException("JSONObject[" + quote(key) +
                 "] not found.");
     }
     return o;
 }

It's just implemented this way, that it will throw exception on null. JSON specification allows nulls, so it's just a quirk. See http://www.json.org/

What to do with this

For optional values this package provides method opt(String) and e.g. optString(String) or optString(String, String), see http://www.docjar.com/docs/api/org/json/JSONObject.html

I would probably use

... = questions.optString("alias"); //if you want `""` as null value

or

... = questions.optString("alias", null); //if you want null

Effectively keep in mind that you're expected to use getString and similar APIs to get required values and optString and similar APIs to get optional values.

Answer 2

You should check if it is null like this:

String alias = "";
if(!json.isNull("alias")){
    alias = json.getString("alias");
} else {
    alias = null;
}

If you don't want to do this, then you might want to use a different json library.