Gson fromJson() returns object with null attrubutes

Question

I'm trying to create some Java objects using this line:

Quiz currentQuiz = gson.fromJson(json, Quiz.class);

But the all I get is this:

Here are my object classes:

Quiz:

public class Quiz {

private String ref;
private String broadcast_dt;
private Question[] questions;

public Quiz() {
    // TODO Auto-generated constructor stub
}

public String getRef() {
    return ref;
}

public void setRef(String ref) {
    this.ref = ref;
}

public String getBroadcast_dt() {
    return broadcast_dt;
}

public void setBroadcast_dt(String broadcast_dt) {
    this.broadcast_dt = broadcast_dt;
}

public Quiz(String ref, String broadcast_dt, Question[] questions) {
    super();
    this.ref = ref;
    this.broadcast_dt = broadcast_dt;
    this.questions = questions;
}

public Question[] getQuestions() {
    return questions;
}

public void setQuestions(Question[] questions) {
    this.questions = questions;
} 
}

Question:

public class Question {

private int question_number;
private String question_text;
private Answer[] answers;

public Question(){

}

public Question(int question_number, String question_text, Answer[] answers) {
    super();
    this.question_number = question_number;
    this.question_text = question_text;
    this.answers = answers;
}

public int getQuestion_number() {
    return question_number;
}

public void setQuestion_number(int question_number) {
    this.question_number = question_number;
}

public String getQuestion_text() {
    return question_text;
}

public void setQuestion_text(String question_text) {
    this.question_text = question_text;
}

public Answer[] getAnswers() {
    return answers;
}

public void setAnswers(Answer[] answers) {
    this.answers = answers;
}
}

Answer:

public class Answer {

private String answer_text;
private boolean correct_yn;

public Answer(){

}

public String getAnswer_text() {
    return answer_text;
}

public void setAnswer_text(String answer_text) {
    this.answer_text = answer_text;
}

public boolean isCorrect_yn() {
    return correct_yn;
}

public void setCorrect_yn(boolean corrent_yn) {
    this.correct_yn = corrent_yn;
}
}

And here is my JSON:

{
"quiz": {
    "ref": "45g36745bu46",
    "broadcast_dt": "2013-03-03T00:00:00Z",
    "questions": [
        {
            "question_number": 1,
            "question_text": "Example question one",
            "answers": [
                {
                    "answer_text": "Answer one",
                    "correct_yn": false
                },
                {
                    "answer_text": "Answer two",
                    "correct_yn": true
                },
                {
                    "answer_text": "Answer three",
                    "correct_yn": false
                }
            ]
        },
        {
            "question_number": 2,
            "question_text": "Question number two",
            "answers": [
                {
                    "answer_text": "Something",
                    "correct_yn": false
                },
                {
                    "answer_text": "Something else",
                    "correct_yn": false
                },
                {
                    "answer_text": "Another thing",
                    "correct_yn": true
                }
            ]
        },
        {
            "question_number": 3,
            "question_text": "And a third question with some additional question text appearing here.",
            "answers": [
                {
                    "answer_text": "Cow",
                    "correct_yn": false
                },
                {
                    "answer_text": "Pig",
                    "correct_yn": true
                }
            ]
        }
    ]
}
}

Any ideas why this happens? I don't get an error message or LogCat output.

Answer 1

In my case I had deleted

@SerializedName("OpCode")
@Expose

parts from my model class which are above the

private Integer opCode;

line. And so Gson could not parse it and so my attributes were null. When I added those lines it fixed.

Answer 2

Try this...

JSONObject js = new JSONObject(jsonString);
for (int i = 0; i < js.length(); i++) {
  JSONObject quiz = js.getJSONObject("quiz");
    for (int j = 0; j < js.length(); j++) {
       String broadcast_dt = quiz.getString("broadcast_dt");
       String ref = quiz.getString("ref");
       JSONArray questions = quiz.getJSONArray("questions");
       for (int k = 0; k < questions.length(); k++) {
        String value = questions.getString(k);
        JSONObject quest = new JSONObject(questions.getString(k));
        int question_number = quest.getInt("question_number");
        String question_text = quest.getString("question_text");
        JSONArray answers = quest.getJSONArray("answers");
        for (int m = 0; m < answers.length(); m++) {
            JSONObject ans = new JSONObject(answers.getString(m));
            Boolean correct_yn = ans.getBoolean("correct_yn");
            String answer_text = ans.getString("answer_text");
        }
    }

}

}

Answer 3

From your json: i see that, at the root level it is something like

{quiz:{quizObject having ref,etc.,}}

So, you need to get one level down to start parsing using gson.

So, try this out,

JSONObject quizObject = json.get("quiz");

Quiz currentQuiz = gson.fromJson(quizObject.toString(), Quiz.class);