Parsing Objects/Arrays from JSON to Java

Question

I'm new to JSON and I'm trying to parse my JSON File into Java, and it works, but I've got Objects/Arrays that contains more arrays and I don't know how to iterate it correctly. This is my JSON File:

{
    "quiz": {
        "sport": {
            "q1": {
                "question": "Which one is correct team name in NBA?",
                "options": [
                    "New York Bulls",
                    "Los Angeles Kings",
                    "Golden State Warriros",
                    "Huston Rocket"
                ],
                "answer": "Huston Rocket"
            }
        },
        "maths": {
            "q1": {
                "question": "5 + 7 = ?",
                "options": [
                    "10",
                    "11",
                    "12",
                    "13"
                ],
                "answer": "12"
            },
            "q2": {
                "question": "12 - 8 = ?",
                "options": [
                    "1",
                    "2",
                    "3",
                    "4"
                ],
                "answer": "4"
            }
        }
    }
}

I don't know how I can get all data in this structure. I mean that I know it's a quiz and the two topics are sport and maths and that each topic has questions and an answer.

I would like to have each value avaiable.

This is my Java Code

JSONParser jsonParser = new JSONParser();

        try
        {

                JSONArray a = (JSONArray) jsonParser.parse("pathToFile");
                for (Object o : a)
                {
                    JSONObject task1 = (JSONObject) o;
                    String name = (String) task1.get("quiz");
                    System.out.println(name);

                    String topic = (String) task1.get("sport");
                    System.out.println(topic);

                }

        }catch (ParseException e)
        {
            e.printStackTrace();
        }
       catch (FileNotFoundException e)
        {
            e.printStackTrace();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }

Can someone explain the logic to me?

What is the relationship between what you want explained and the code you have posted? — Scott Hunter
– Scott Hunter, Commented Jan 30, 2020 at 15:21
It would be useful to know which JSON parsing library you're using — JonK
– JonK, Commented Jan 30, 2020 at 15:30
I would use GSON. You will need to create a few classes though. Quiz, Sport, and Maths. If you have control of creating the JSON, you should make q1, q2 an array in my opinion. — SedJ601
– SedJ601, Commented Jan 30, 2020 at 15:46
i recommend to create the classes, after you can use the google's library — Alejandro Gonzalez
– Alejandro Gonzalez, Commented Jan 30, 2020 at 16:15

Tschallacka · Accepted Answer · 2020-01-30 16:00:11Z

2

Assuming you don't want to use GSON and let loose your own logic on handling the quiz objects:
Analyze the JSON and create them logical objects for the values. Then when you read the JSON, you create the objects as required and attach them as needed.

You'd need a Quiz, Category, Question and Option objects.

then your code would become something like this(psuedo code, not tested if it actually works):

 public Quiz createQuiz(JSONObject raw) 
 {
     Quiz quiz = new Quiz();

     Iterator<String> keys = raw.keys();
     while(keys.hasNext()) {
        String key = keys.next();
        if (raw.get(key) instanceof JSONObject) { 
           JSONObject rawCategory = (JSONObject)raw.get(key);
           quiz.addCategory(this.createCategory(key, rawCategory));
        }
    } 
    return quiz;
}
public Category createCategory(String name, JSONObject raw) 
{
    Category category = new Category(name);
    Iterator<String> keys = raw.keys();
     while(keys.hasNext()) {
        String key = keys.next();
        if (raw.get(key) instanceof JSONObject) { 
           JSONObject rawQuestion = (JSONObject)raw.get(key);
           category.addQuestion(this.createQuestion(key, rawQuestion));
        }
    } 
   return category;
}

public Category createQuestion(String name, JSONObject raw) 
{
    Question question = new Question(name);
    if(raw.hasKey("question") && raw.get("question") instanceof String) {
       question.setQuestionText((String) raw.get("question"));
    }
    if(raw.hasKey("answer") && raw.get("answer") instanceof String) {
       question.setAnswerText((String) raw.get("answer"));
    }
    if(raw.hasKey("options") && raw.get("options") instanceof JSONArray) {
       JSONArray rawOptions = (JSONArray)raw.get("options");
       for(Object rawOption : rawOptions) {
          if(rawOption instanceof String) {
             question.addOption(this.createOption((String) rawOption));
          } 
       }
    }
   return question;
}

answered Jan 30, 2020 at 16:00

Tschallacka

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2 Comments

Marie_Jane98 Over a year ago

All I want to do is to read out my data from my json and use them in my code. Is it necessary/easier to have objects and classes to get these data?

Tschallacka Over a year ago

@Marie_Jane98 yes. In the future and now it will be easier on you. When you use objects you will always know what type of data is where, your editor can autocomplete and you can add more fuctionality. When you return in a few months to add a few features and you don't have an example json handy, and no objects defined, you'll hate to have to restructure logic and deeply nest functionality. You'll create spaghetti code. I'd you don't know that term, google it

Alejandro Gonzalez · Accepted Answer · 2020-01-30 16:13:50Z

The first, you need the create the class, it is more easy that compare the object

This link can help you to convert the json to classes

https://www.site24x7.com/tools/json-to-java.html

They are the classes that was generated

/* * To change this license header, choose License Headers in Project Properties. * To change this template file, choose Tools | Templates * and open the template in the editor. */ package com.examen.overflow;

/**
 *
 * @author wilso
 */
public class Dto {

    private Quiz quiz;

    public Quiz getQuiz() {
        return quiz;
    }

    public void setQuiz(Quiz quiz) {
        this.quiz = quiz;
    }
}


/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.examen.overflow;

/**
 *
 * @author wilso
 */
public class Maths {

    private Question q1;
    private Question q2;

    // Getter Methods 
    public Question getQ1() {
        return q1;
    }

    public Question getQ2() {
        return q2;
    }

    // Setter Methods 
    public void setQ1(Question q1) {
        this.q1 = q1;
    }

    public void setQ2(Question q2) {
        this.q2 = q2;
    }
}


/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.examen.overflow;

import java.util.List;

/**
 *
 * @author wilso
 */
public class Question {

    private String answer;
    private List<String> options;
    private String question;

    public String getAnswer() {
        return answer;
    }

    public void setAnswer(String answer) {
        this.answer = answer;
    }

    public List<String> getOptions() {
        return options;
    }

    public void setOptions(List<String> options) {
        this.options = options;
    }

    public String getQuestion() {
        return question;
    }

    public void setQuestion(String question) {
        this.question = question;
    }

}


/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.examen.overflow;

/**
 *
 * @author wilso
 */
public class Quiz {

    private Sport sport;
    private Maths maths;

    public Sport getSportObject() {
        return sport;
    }

    public void setSportObject(Sport sport) {
        this.sport = sport;
    }

    public Maths getMathsObject() {
        return maths;
    }

    public void setMathsObject(Maths maths) {
        this.maths = maths;
    }

}


/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.examen.overflow;

/**
 *
 * @author wilso
 */
public class Sport {

    Question q1;

    // Getter Methods 
    public Question getQ1() {
        return q1;
    }

    // Setter Methods 
    public void setQ1(Question question) {
        this.q1 = question;
    }
}

When you have the classes, you only need to do the next

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.examen.overflow;

import com.google.gson.Gson;

public class Convert {

    public static void main(String[] args) {
        String json = "{\n"
                + "    \"quiz\": {\n"
                + "        \"sport\": {\n"
                + "            \"q1\": {\n"
                + "                \"question\": \"Which one is correct team name in NBA?\",\n"
                + "                \"options\": [\n"
                + "                    \"New York Bulls\",\n"
                + "                    \"Los Angeles Kings\",\n"
                + "                    \"Golden State Warriros\",\n"
                + "                    \"Huston Rocket\"\n"
                + "                ],\n"
                + "                \"answer\": \"Huston Rocket\"\n"
                + "            }\n"
                + "        },\n"
                + "        \"maths\": {\n"
                + "            \"q1\": {\n"
                + "                \"question\": \"5 + 7 = ?\",\n"
                + "                \"options\": [\n"
                + "                    \"10\",\n"
                + "                    \"11\",\n"
                + "                    \"12\",\n"
                + "                    \"13\"\n"
                + "                ],\n"
                + "                \"answer\": \"12\"\n"
                + "            },\n"
                + "            \"q2\": {\n"
                + "                \"question\": \"12 - 8 = ?\",\n"
                + "                \"options\": [\n"
                + "                    \"1\",\n"
                + "                    \"2\",\n"
                + "                    \"3\",\n"
                + "                    \"4\"\n"
                + "                ],\n"
                + "                \"answer\": \"4\"\n"
                + "            }\n"
                + "        }\n"
                + "    }\n"
                + "}";
        Dto quiz = new Gson().fromJson(json, Dto.class);
        System.out.println(quiz);
        //Iterate object
        for (String option : quiz.getQuiz().getMathsObject().getQ1().getOptions()) {
            System.out.println(option);
        }
    }
}

So I tried as you suggested and I can follow the logic, but I don't know how to do it with the simply json libary. They haven't an object like new Gson (or new JSON)
When you said the next: I don't know how to do it with the simply json libary. They haven't an object like new Gson (or new JSON). What do you mean?

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