I need to map JSON
obj to a class and its arrays to ArrayList
in Android
and it should have all the children data as well. (with nested arraylists too) and i need to convert updated data list again to jsonobject
my json string is
{
"type": "already_planted",
"crops": [
{
"crop_id": 1,
"crop_name": "apple",
"crop_details": [
{
"created_id": "2017-01-17",
"questions": [
{
"plants": "10"
},
{
"planted_by": "A person"
}
]
},
{
"created_id": "2017-01-30",
"questions": [
{
"plants": "15"
},
{
"planted_by": "B person"
}
]
}
]
},
{
"crop_id": 2,
"crop_name": "Cashew",
"crop_details": [
{
"created_id": "2017-01-17",
"questions": [
{
"plants": "11"
},
{
"planted_by": "c person"
}
]
}
]
}
]
}
You can map the data types of your business model into JSON by using the examples. Data in JSON is either an object or an array. A JSON object is an unordered collection of names and values. A JSON array is an ordered sequence of values.
We can convert a JSON to Java Object using the readValue() method of ObjectMapper class, this method deserializes a JSON content from given JSON content String.
First of all, you need to create the class that you are going to map JSON inside.
Fortunately, there is a website that can do it for you here
secondly, you can use google Gson library for easy mapping
1. add the dependency.
dependencies {
implementation 'com.google.code.gson:gson:2.8.6'
}
2. from your object to JSON.
MyData data =new MyData() ; //initialize the constructor
Gson gson = new Gson();
String Json = gson.toJson(data ); //see firstly above above
//now you have the json string do whatever.
3. from JSON to object .
String jsonString =doSthToGetJson(); //http request
MyData data =new MyData() ;
Gson gson = new Gson();
data= gson.fromJson(jsonString,MyData.class);
//now you have Pojo do whatever
for more information about gson see this tutorial.
If you use JsonObject
, you can define your entity class
as this:
public class Entity {
String type;
List<Crops> crops;
}
public class Crops {
long crop_id;
String crop_name;
List<CropDetail> crop_details;
}
public class CropDetail {
String created_id;
List<Question> questions;
}
public class Question {
int plants;
String planted_by;
}
public void convert(String json){
JsonObject jsonObject = new JsonObject(jsonstring);
Entity entity = new Entity();
entity.type = jsonObject.optString("type");
entity.crops = new ArrayList<>();
JsonArray arr = jsonObject.optJSONArray("crops");
for (int i = 0; i < arr.length(); i++) {
JSONObject crops = arr.optJSONObject(i);
Crops cps = new Crops();
cps.crop_id = crops.optLong("crop_id");
cps.crop_name = crops.optString("crop_name");
cps.crop_details = new ArrayList<>();
JsonArray details = crops.optJsonArray("crop_details");
// some other serialize codes
..........
}
}
So you can nested to convert your json string to an entity class.
Here is how I do it without any packages, this do the work for me for small use cases:
My modal class:
package prog.com.quizapp.models;
import org.json.JSONException;
import org.json.JSONObject;
public class Question {
private String question;
private String correct_answer;
private String answer_a;
private String answer_b;
private String answer_c;
private String answer_d;
public Question() {
}
public Question(String question, String answer_a, String answer_b, String answer_c, String answer_d, String correct_answer) {
this.question = question;
this.answer_a = answer_a;
this.answer_b = answer_b;
this.answer_c = answer_c;
this.answer_d = answer_d;
this.correct_answer = correct_answer;
}
public String getQuestion() {
return question;
}
public void setQuestion(String question) {
this.question = question;
}
public String getCorrect_answer() {
return correct_answer;
}
public void setCorrect_answer(String correct_answer) {
this.correct_answer = correct_answer;
}
public String getAnswer_a() {
return answer_a;
}
public void setAnswer_a(String answer_a) {
this.answer_a = answer_a;
}
public String getAnswer_b() {
return answer_b;
}
public void setAnswer_b(String answer_b) {
this.answer_b = answer_b;
}
public String getAnswer_c() {
return answer_c;
}
public void setAnswer_c(String answer_c) {
this.answer_c = answer_c;
}
public String getAnswer_d() {
return answer_d;
}
public void setAnswer_d(String answer_d) {
this.answer_d = answer_d;
}
@Override
public String toString() {
return "Question{" +
"question='" + question + '\'' +
", correct_answer='" + correct_answer + '\'' +
", answer_a='" + answer_a + '\'' +
", answer_b='" + answer_b + '\'' +
", answer_c='" + answer_c + '\'' +
", answer_d='" + answer_d + '\'' +
'}';
}
public static Question fromJson(JSONObject obj) throws JSONException {
return new Question(
obj.getString("question"),
obj.getString("answer_a"),
obj.getString("answer_b"),
obj.getString("answer_c"),
obj.getString("answer_d"),
obj.getString("correct_answer"));
}
}
And I have another class to get the json file from assets directory and mapped JsonObject
to my model class Question
:
package prog.com.quizapp.utils;
import android.content.Context;
import android.util.Log;
import org.json.JSONObject;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Iterator;
import prog.com.quizapp.models.Question;
public class JsonSqlQueryMapper {
private Context mContext;
public JsonSqlQueryMapper(Context context) {
this.mContext = context;
}
private static final String TAG = "JsonSqlQueryMapper";
public JSONObject loadJSONFromAsset() {
String json = null;
try {
InputStream is = mContext.getAssets().open("quiz_app.json");
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
json = new String(buffer, "UTF-8");
} catch (IOException ex) {
ex.printStackTrace();
return null;
}
try {
JSONObject quizObject = new JSONObject(json).getJSONObject("quiz");
return quizObject;
} catch (Exception e) {
Log.d(TAG, "loadJSONFromAsset: " + e.getMessage());
return null;
}
}
public ArrayList<Question> generateInsertQueryForJsonObjects() {
ArrayList<Question> questions = new ArrayList<>();
JSONObject jsonObject = loadJSONFromAsset();
try {
Iterator<String> iter = jsonObject.keys();
while (iter.hasNext()) {
String key = iter.next();
JSONObject value = jsonObject.getJSONObject(key);
Question question = Question.fromJson(value.getJSONObject("question_two"));
questions.add(question);
Log.d(TAG, "generateInsertQueryForJsonObjects: " + question.getAnswer_a());
}
} catch (Exception e) {
e.printStackTrace();
}
return questions;
}
}
And in my MainActivity
-> onCreate
:
JsonSqlQueryMapper mapper = new JsonSqlQueryMapper(MainActivity.this);
mapper.generateInsertQueryForJsonObjects();
To check that everything working as I want. Here is the json file if you want to check https://github.com/Blasanka/android_quiz_app/blob/sqlite_db_app/app/src/main/assets/quiz_app.json
Regards!
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With