How can I prevent gson from converting integers to doubles

Question

I\'ve got integers in my json, and I do not want gson to convert them to doubles. The following does not work:

@Test
public void keepsIntsAsIs(){
    String          


        

Answer 1

You have to use public T fromJson(JsonElement json, Type typeOfT)

public void keepsIntsAsIs(){
        String json="[{\"id\":1,\"quantity\":2},{\"id\":3,\"quantity\":4}]";
        GsonBuilder gsonBuilder = new GsonBuilder();
        Gson gson = gsonBuilder.create();
        Type objectListType = new TypeToken>>(){}.getType();
        List> l = gson.fromJson(json, objectListType);
        for(Map item : l){
            System.out.println(item);
        }
    }

Output:

{id=1, quantity=2}
{id=3, quantity=4}

[EDIT]

If not all fields are integers then one way to resolve this is to map the json to an object and define a deserializer for that object.

Below is the example.

I am mapping json to IdQuantityName and IdQuantityDeserializer is the json deserializer.

package com.foo;



import java.lang.reflect.Type;
import java.util.List;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import com.google.gson.reflect.TypeToken;

public class TestGSON {

public void keepsIntsAsIs(){
    String json="[{\"id\":1,\"quantity\":2,\"name\":\"apple\"},{\"id\":3,\"quantity\":4,\"name\":\"orange\"}]";
    GsonBuilder gsonBuilder = new GsonBuilder();
    gsonBuilder.registerTypeHierarchyAdapter(IdQuantityName.class, new IdQuantityDeserializer());
    gsonBuilder.registerTypeAdapter(IdQuantityName.class, new IdQuantityDeserializer());

    Gson gson = gsonBuilder.create();
    Type objectListType = new TypeToken>(){}.getType();
    List l = gson.fromJson(json,objectListType);
    for (IdQuantityName idQuantityName : l) {
        System.out.println(idQuantityName);
    }
}



class IdQuantityName{
    private int id;
    private Object quantity;
    private String name;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public Object getQuantity() {
        return quantity;
    }
    public void setQuantity(Object quantity) {
        this.quantity = quantity;
    }
    public Object getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "IdQuantityName [id=" + id + ", quantity=" + quantity
                + ", name=" + name + "]";
    }



}
private  class IdQuantityDeserializer implements JsonDeserializer{

    @Override
    public IdQuantityName deserialize(JsonElement json, Type typeOfT,
            JsonDeserializationContext context) throws JsonParseException {

        JsonObject jo = json.getAsJsonObject();

        IdQuantityName idq = new IdQuantityName();
        idq.setId(jo.get("id").getAsInt());
        idq.setName(jo.get("name").getAsString());

        JsonElement jsonElement = jo.get("quantity");
        if(jsonElement instanceof JsonPrimitive){
            if(((JsonPrimitive) jsonElement).isNumber()){
                idq.setQuantity(jsonElement.getAsInt());
            };
        }
        return idq;

    }
}
public static void main(String[] args) {
    new TestGSON().keepsIntsAsIs();
}
}