how to map a JSON to a java model class

Question

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"
              }
            ]
          }
        ]
      }
    ]
  }

Answer 1

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 {
          compile 'com.google.code.gson:gson:2.8.2'
         }  

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.

Answer 2

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.