Mapping JSON to simple Java subclass

Question

I'm trying to move from default Json API in Android to GSON (or Jackson). But I'm stuck at trying to convert JSONObject to Java object. I've read many tutorials, but found nothing helpful.

I have these two classes (these are just for simplicity):

public class Animal {
    @SerializedName("id")
    private int id;

    //getters and setters
}

public class Dog extends Animal{
    @SerializedName("Name")
    private String name;

    //getters and setters
}

The JSON that I'm trying to map to Dog class is this:

{
   "id" : "1",
   "Name" : "Fluffy"
}

I'm using this code:

Gson gson = new Gson();
Dog dog = gson.fromJson(jsonObject.toString(), Dog.class);

Name is being mapped ok, but id is not.

How can I achieve this with GSON (or Jackson) libraries, if it's simpler?

Answer 1

Your code should work fine. Try checking what jsonObject.toString() returns. Whether that matches the actual json or not. Example

import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;

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

class Animal {
    private int id;

    public int getId() {
        return id;
    }

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

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

class Dog extends Animal{
    @SerializedName("Name")
    private String name;

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "Dog [name=" + name + ", Id=" + getId() + "]";
    }


}
public class GSonParser {

    public static void main(String[] args) throws Exception {
        String json = "{\"id\" : \"1\", \"Name\" : \"Fluffy\"}";
        JSONParser parser = new JSONParser();
        JSONObject jsonObject = (JSONObject) parser.parse(json);
        Gson gson = new Gson();
        Dog dog = gson.fromJson(jsonObject.toString(), Dog.class);
        System.out.println(dog); // Prints "Dog [name=Fluffy, Id=1]"
    }

}

Answer 2

For Jackson I use this code

private static ObjectMapper configMapper() {
    ObjectMapper mapper = new ObjectMapper();
    mapper.setVisibilityChecker(mapper.getSerializationConfig().getDefaultVisibilityChecker()
            .withFieldVisibility(JsonAutoDetect.Visibility.PUBLIC_ONLY)
            .withGetterVisibility(JsonAutoDetect.Visibility.PUBLIC_ONLY)
            .withSetterVisibility(JsonAutoDetect.Visibility.PUBLIC_ONLY)
            .withCreatorVisibility(JsonAutoDetect.Visibility.PUBLIC_ONLY));
    mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    return mapper;
}
private Dog readDog(String json) {
 Dog ret = null;
    if (json != null) {
        ObjectMapper mapper = configMapper();
        try {
            ret = mapper.readValue(json, Dog.class);
        } catch (Exception e) {
            Log.e("tag", Log.getStackTraceString(e));
            return null;
        } 
    }
 return ret;
}

Hope it works for you as well.