How to parse nested JSON data in Android with Retrofit and Gson

Question

I'm familiar with parsing basic JSON data with Retrofit, but struggling with implementation of correct POJO objects for this JSON responce.

Here is JSON data:

{
    "observations": [
      {
        "id": "0",
        "type": "1st type",
        "data": [
            {
              "name": "some_name",
              "result": "some_result"
            }
          ]
      },
      {
        "id": "1",
        "type": "2nd type",
        "data": [
            {
              "name2": "some_name2",
              "measurement": "some_measurement",
              "field": "some_field",
              "result2": "some_result2"
            }
          ]
      }
    ]
}

I have created Classes for both Observation types:

public class DataType1{

    @SerializedName("name")
    @Expose
    private String name;
    @SerializedName("measurement")
    @Expose
    private String measurement;
    @SerializedName("field")
    @Expose
    private String field;
    @SerializedName("result")
    @Expose
    private String result;
}

public class DataType2 {
    @SerializedName("name")
    @Expose
    private String name;
    @SerializedName("result")
    @Expose
    private String result;
}

The general idea what by "type" I determine the type of data and send it to corresponding class:

if(response.body().getType.equals("1st type"))
{
    Gson gson = new GsonBuilder().create();
    DataType1 data = gson.fromJson(response.body().getObservation, DataType1.class);
}

I assume, next I have to create a separate ObservationsResponce class to get a List of observations:

public class Observation {
    @SerializedName("id")
    @Expose
    private String id;
    @SerializedName("type")
    @Expose
    private String type;
    @SerializedName("observation")
    @Expose
    private List<??What Should Be Here??> observation = null;
}

But the problem is that observations can have a different data types and a so different fields inside. In that case which class should this List be?

@primo I updated the answer with different names. Am I getting correctly, that list should be `List` in that case? — Alex, May 07 '19 at 12:36
you know you should follow this link http://pojo.sodhanalibrary.com/Convert\ — primo, May 07 '19 at 12:36
I've tried converters, but they don't take into account type difference. So I get class only for the 1st type without "measurement" and "field". — Alex, May 07 '19 at 12:40
either custom deserializer or ... `class Base { ... }` `class MoreProps extends Base { ... }` `class EvenMoreProps extends MoreProps {...}` and use `List` ... then — Selvin, May 07 '19 at 12:40
I found a problem in your json file, make sure your JSON file is correct — Shudipto Trafder, May 07 '19 at 12:41
this thing only happens if there is difference in list but you will get POJO structure — primo, May 07 '19 at 12:42
@ShudiptoTrafder which problem exactly? I've run it through a couple constructors, no errors shown. — Alex, May 07 '19 at 12:43
I think your json is valid.Go through this link https://jsonlint.com/ — primo, May 07 '19 at 12:44
I found the name in the first list and name2 in the second list, the key should be the same, to create POJO class — Shudipto Trafder, May 07 '19 at 12:46
@primo so I should just create Data.class which will include all the possible fields? — Alex, May 07 '19 at 12:46
@ShudiptoTrafder thats the point of the question. I can't figure out what should I do when fields is different. — Alex, May 07 '19 at 12:47

score 1 · Answer 1 · answered May 07 '19 at 12:54

MyObservation.java


public class MyObservation
{
    private Observations[] observations;

    public Observations[] getObservations ()
    {
        return observations;
    }

    public void setObservations (Observations[] observations)
    {
        this.observations = observations;
    }

    @Override
    public String toString()
    {
        return "MyObservation [observations = "+observations+"]";
    }
}


Observations.java

public class Observations
{
    private Data[] data;

    private String id;

    private String type;

    public Data[] getData ()
    {
        return data;
    }

    public void setData (Data[] data)
    {
        this.data = data;
    }

    public String getId ()
    {
        return id;
    }

    public void setId (String id)
    {
        this.id = id;
    }

    public String getType ()
    {
        return type;
    }

    public void setType (String type)
    {
        this.type = type;
    }

    @Override
    public String toString()
    {
        return "ClassPojo [data = "+data+", id = "+id+", type = "+type+"]";
    }
}

Data.java

public class Data
{
    private String result;

    private String name;


    //add these fields manually
    private String measurement;

    private String field;

    public String getResult ()
    {
        return result;
    }

    public void setResult (String result)
    {
        this.result = result;
    }


    public String getMeasurement ()
    {
        return measurement;
    }

    public void setMeasurement (String measurement)
    {
        this.measurement = measurement;
    }

    public String getField ()
    {
        return field;
    }

    public void setField (String field)
    {
        this.field = field;
    }


    public String getName ()
    {
        return name;
    }

    public void setName (String name)
    {
        this.name = name;
    }

    @Override
    public String toString()
    {
        return "ClassPojo [result = "+result+", name = "+name+"]";
    }
}

And its better to use same key and then also if you want different keys and want to generate POJO then use this link

The link you provided is actually very helpful, thanks. – Alex May 07 '19 at 13:02 — Alex, May 07 '19 at 13:02

score 0 · Answer 2 · answered May 07 '19 at 12:55

Check this pojo class I am not sure it's work or not

package com.example;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

import java.util.List;

public class Datum {

@SerializedName("name")
@Expose
private String name;
@SerializedName("result")
@Expose
private String result;
@SerializedName("name2")
@Expose
private String name2;
@SerializedName("measurement")
@Expose
private String measurement;
@SerializedName("field")
@Expose
private String field;
@SerializedName("result2")
@Expose
private String result2;

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getResult() {
    return result;
}

public void setResult(String result) {
    this.result = result;
}

public String getName2() {
    return name2;
}

public void setName2(String name2) {
    this.name2 = name2;
}

public String getMeasurement() {
    return measurement;
}

public void setMeasurement(String measurement) {
    this.measurement = measurement;
}

public String getField() {
    return field;
}

public void setField(String field) {
    this.field = field;
}

public String getResult2() {
    return result2;
}

public void setResult2(String result2) {
    this.result2 = result2;
}

}

class Example {

@SerializedName("observations")
@Expose
private List<Observation> observations = null;

public List<Observation> getObservations() {
    return observations;
}

public void setObservations(List<Observation> observations) {
    this.observations = observations;
}

}

class Observation {

@SerializedName("id")
@Expose
private String id;
@SerializedName("type")
@Expose
private String type;
@SerializedName("data")
@Expose
private List<Datum> data = null;

public String getId() {
    return id;
}

public void setId(String id) {
    this.id = id;
}

public String getType() {
    return type;
}

public void setType(String type) {
    this.type = type;
}

public List<Datum> getData() {
    return data;
}

public void setData(List<Datum> data) {
    this.data = data;
}

}

It's generated with jsonschema2pojo.org. – Alex May 07 '19 at 12:58 — Alex, May 07 '19 at 12:58
@Alex, I generate from that site – Shudipto Trafder May 07 '19 at 13:00 — Shudipto Trafder, May 07 '19 at 13:00

How to parse nested JSON data in Android with Retrofit and Gson

2 Answers2