How to convert JSON response as shown below to POJO using Gson? - json

Question

The format of my JSON is :
{"abc": [{
"field_1": "string_1",
"value": 0.304
},
{
"field_1": "string_2",
"value": 0.193
}]}
"abc" is variable, "field_1" and "value" are field names. I want a class in Java which stores this JSON in some format for example:
String t; // should store "abc"
List<myClass> myClassObject; // myClass should contain "field_1" and "value"
myClass.java
String field_1; // should store "string_1" and "string_2"
Double value; // should store 0.304 and 0.193
I want the class myClass.java because in future I may want to add more metadata in JSON response. This is complex object mapping, but I am not able to figure out what should my class be looking like in order to store the JSON response.

Answer 1

For root object do not create new POJO just use Map. Example could look like below:
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.SerializedName;
import com.google.gson.reflect.TypeToken;
import java.io.File;
import java.io.FileReader;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Map;
public class GsonApp {
public static void main(String[] args) throws Exception {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
Gson gson = new GsonBuilder().create();
Type mapType = new TypeToken<Map<String, List<Item>>>() {
}.getType();
Map<String, List<Item>> map = gson.fromJson(new FileReader(jsonFile), mapType);
Map.Entry<String, List<Item>> first = map.entrySet().stream().findFirst().get();
Items items = new Items(first.getKey(), first.getValue());
System.out.println(items);
}
}
class Items {
private final String key;
private final List<Item> items;
public Items(String key, List<Item> items) {
this.key = key;
this.items = items;
}
public String getKey() {
return key;
}
public List<Item> getItems() {
return items;
}
#Override
public String toString() {
return "Items{" +
"key='" + key + '\'' +
", items=" + items +
'}';
}
}
class Item {
#SerializedName("field_1")
private String field;
private Double value;
public String getField() {
return field;
}
public void setField(String field) {
this.field = field;
}
public Double getValue() {
return value;
}
public void setValue(Double value) {
this.value = value;
}
#Override
public String toString() {
return "Item{" +
"field='" + field + '\'' +
", value=" + value +
'}';
}
}
Above code prints:
Items{key='abc', items=[Item{field='string_1', value=0.304}, Item{field='string_2', value=0.193}]}

Answer 2

I'm sharing you the sample code:
Main method:
import com.google.gson.Gson;
public class GsonConversion {
public static void main(String[] args) {
String json = "{\"abc\": [{" +
" \"field_1\": \"string_1\"," +
" \"value\": 0.304" +
"}," +
"{" +
" \"field_1\": \"string_2\"," +
" \"value\": 0.193" +
"}]}";
Gson gson = new Gson();
Type mapType = new TypeToken<Map<String, List<Data>>>() {
}.getType();
Map<String, List<Data>> map = gson.fromJson(json, mapType);
Model model= new Model();
map.entrySet().stream().forEach(entry->{
model.setT(entry.getKey());
model.setAbc(entry.getValue());
});
System.out.println("Key:"+model.getT());
model.getAbc().stream().forEach(x->{
System.out.println("Field:"+x.getField_1()+" Value:"+x.getValue());
});
}
}
Parent Model Objects:
i) Model Class
import java.util.ArrayList;
public class Model {
private String t;
private ArrayList<Data> abc = new ArrayList<>();
public String getT() {
return t;
}
public void setT(String t) {
this.t = t;
}
public ArrayList<Data> getAbc() {
return abc;
}
public void setAbc(ArrayList<Data> abc) {
this.abc = abc;
}
}
ii) Data Class
public class Data {
private String field_1;
private Double value;
public Data() {
}
public String getField_1() {
return field_1;
}
public void setField_1(String field_1) {
this.field_1 = field_1;
}
public Double getValue() {
return value;
}
public void setValue(Double value) {
this.value = value;
}
}