Jackson vs. Gson vs. JSON-B | Java JSON Polymorphic type handling - Its All Binary

In this article we will compare polymorphic type handling in different JSON binding libraries in Java i.e. Jackson vs. Gson vs. JSON-B (Eclipse Yasson)

For complete comparison of top JSON libraries & their features, visit below article.

Jackson vs. Gson vs. JSON-B vs. JSON-P vs. org.JSON vs. Jsonpath | Java JSON libraries features comparison

Polymorphic JSON bound POJOs

As Java is object oriented language, JSON bound POJOs might have polymorphic nature. For example, Car (abstraction) with Honda & Tesla as concrete implementations.

public class Garage {
	private Car car;

	... Getter and setter ...
}

public class Garage {

private Car car;

... Getter and setter ...

}

public abstract class Car {
	private String make;

	... Getter and setter ...
}

public abstract class Car {

private String make;

... Getter and setter ...

}

public class Honda extends Car {
	@Override
	public String toString() {
		return "Driving Honda!";
	}
}

public class Honda extends Car {

@Override

public String toString() {

return "Driving Honda!";

}

public class Tesla extends Car {
	@Override
	public String toString() {
		return "Driving Tesla!";
	}
}

public class Tesla extends Car {

@Override

public String toString() {

return "Driving Tesla!";

}

Test JSON

For above POJOs, we will use these JSONs to test different libraries.

{
	"car": {
		"make": "Honda"
	}
}

{

"car": {

"make": "Honda"

}

{
	"car": {
		"make": "Tesla"
	}
}

{

"car": {

"make": "Tesla"

}

Jackson

In jackson, to achieve polymorphic handling of JSON bound POJOs, just add these annotations on Car.java i.e. abstract class. To identify subclass to use during deserialization, value of ‘make’ field from subclasses will be used to determine which sub class will be used to instantiate object.

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "make")
@JsonSubTypes({ @JsonSubTypes.Type(value = Honda.class, name = "Honda"),
		@JsonSubTypes.Type(value = Tesla.class, name = "Tesla") })
public abstract class Car {
	private String make;
......
}

import com.fasterxml.jackson.annotation.JsonSubTypes;

import com.fasterxml.jackson.annotation.JsonTypeInfo;

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "make")

@JsonSubTypes({ @JsonSubTypes.Type(value = Honda.class, name = "Honda"),

@JsonSubTypes.Type(value = Tesla.class, name = "Tesla") })

public abstract class Car {

private String make;

......

}

Now lets deserialize JSON using above annotated POJO & test json files.

import java.io.File;
import java.io.IOException;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonPolymorphism {

	public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
		ObjectMapper objectMapper = new ObjectMapper();

		Garage garage_1 = objectMapper.readValue(new File("garage-1.json"), Garage.class);
		System.out.println(garage_1.getCar());

		Garage garage_2 = objectMapper.readValue(new File("garage-2.json"), Garage.class);
		System.out.println(garage_2.getCar());
	}

}

import java.io.File;

import java.io.IOException;

import com.fasterxml.jackson.core.JsonParseException;

import com.fasterxml.jackson.databind.JsonMappingException;

import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonPolymorphism {

public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {

ObjectMapper objectMapper = new ObjectMapper();

Garage garage_1 = objectMapper.readValue(new File("garage-1.json"), Garage.class);

System.out.println(garage_1.getCar());

Garage garage_2 = objectMapper.readValue(new File("garage-2.json"), Garage.class);

System.out.println(garage_2.getCar());

}

Driving Honda!
Driving Tesla!

1 2	Driving Honda! Driving Tesla!

GSON

GSON does not provide out of the box way to handle polymorphic type handling, but we can create custom deserializer to achieve this effect.

public class CarDeserializer implements JsonDeserializer<Car> {

	@Override
	public Car deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
			throws com.google.gson.JsonParseException {
		JsonObject jsonObj = json.getAsJsonObject();
		String make = jsonObj.get("make").getAsString();

		switch (make) {
		case "Honda":
			return context.deserialize(jsonObj, Honda.class);
		case "Tesla":
			return context.deserialize(jsonObj, Tesla.class);
		}

		return null;
	}
}

public class CarDeserializer implements JsonDeserializer<Car> {

@Override

public Car deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)

throws com.google.gson.JsonParseException {

JsonObject jsonObj = json.getAsJsonObject();

String make = jsonObj.get("make").getAsString();

switch (make) {

case "Honda":

return context.deserialize(jsonObj, Honda.class);

case "Tesla":

return context.deserialize(jsonObj, Tesla.class);

}

return null;

}

Now lets deserialize JSON using above CarDeserializer & test json files.

import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.lang.reflect.Type;

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;

public class GsonPolymorphism {

	public static void main(String[] args) throws IOException {
		Gson gson = new GsonBuilder().registerTypeAdapter(Car.class, new CarDeserializer()).create();

		Garage garage_1 = gson.fromJson(new FileReader(new File("garage-1.json")), Garage.class);
		System.out.println(garage_1.getCar());

		Garage garage_2 = gson.fromJson(new FileReader(new File("garage-2.json")), Garage.class);
		System.out.println(garage_2.getCar());
	}
}

import java.io.File;

import java.io.FileReader;

import java.io.IOException;

import java.lang.reflect.Type;

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;

public class GsonPolymorphism {

public static void main(String[] args) throws IOException {

Gson gson = new GsonBuilder().registerTypeAdapter(Car.class, new CarDeserializer()).create();

Garage garage_1 = gson.fromJson(new FileReader(new File("garage-1.json")), Garage.class);

System.out.println(garage_1.getCar());

Garage garage_2 = gson.fromJson(new FileReader(new File("garage-2.json")), Garage.class);

System.out.println(garage_2.getCar());

}

JSON-B

JSON-B also does not provide specific easy annotation to achieve this so we can create deserializer to achieve this.

import java.lang.reflect.Type;

import javax.json.JsonObject;
import javax.json.bind.serializer.DeserializationContext;
import javax.json.bind.serializer.JsonbDeserializer;
import javax.json.stream.JsonParser;

public class CarDeserializer implements JsonbDeserializer<Car> {

	@Override
	public Car deserialize(JsonParser parser, DeserializationContext context, Type rtType) {
		JsonObject jsonObj = parser.getObject();
		String make = jsonObj.getString("make");

		switch (make) {
		case "Honda":
			return context.deserialize(Honda.class, parser);
		case "Tesla":
			return context.deserialize(Tesla.class, parser);
		}

		return null;
	}
}

import java.lang.reflect.Type;

import javax.json.JsonObject;

import javax.json.bind.serializer.DeserializationContext;

import javax.json.bind.serializer.JsonbDeserializer;

import javax.json.stream.JsonParser;

public class CarDeserializer implements JsonbDeserializer<Car> {

@Override

public Car deserialize(JsonParser parser, DeserializationContext context, Type rtType) {

JsonObject jsonObj = parser.getObject();

String make = jsonObj.getString("make");

switch (make) {

case "Honda":

return context.deserialize(Honda.class, parser);

case "Tesla":

return context.deserialize(Tesla.class, parser);

}

return null;

}

Put annotation on Car.java to user CarDeserializer

import javax.json.bind.annotation.JsonbTypeDeserializer;

@JsonbTypeDeserializer(CarDeserializer.class)
public abstract class Car {
	....
}

import javax.json.bind.annotation.JsonbTypeDeserializer;

@JsonbTypeDeserializer(CarDeserializer.class)

public abstract class Car {

....

}

Now lets deserialize JSON using above CarDeserializer & test json files.

import java.io.File;
import java.io.FileReader;
import java.io.IOException;

import javax.json.bind.Jsonb;
import javax.json.bind.JsonbBuilder;

public class JsonBPolymorphism {

	public static void main(String[] args) throws IOException {

		Jsonb jsonb = JsonbBuilder.create();

		/*
		 * You can also register deserializer here instead of annotation in Car.java
		 * 
		 * Jsonb jsonb = JsonbBuilder.create(new JsonbConfig().withDeserializers(new
		 * CarDeserializer()));
		 */

		Garage garage_1 = jsonb.fromJson(new FileReader(new File("garage-1.json")), Garage.class);
		System.out.println(garage_1.getCar());

		Garage garage_2 = jsonb.fromJson(new FileReader(new File("garage-2.json")), Garage.class);
		System.out.println(garage_2.getCar());

	}
}

import java.io.File;

import java.io.FileReader;

import java.io.IOException;

import javax.json.bind.Jsonb;

import javax.json.bind.JsonbBuilder;

public class JsonBPolymorphism {

public static void main(String[] args) throws IOException {

Jsonb jsonb = JsonbBuilder.create();

* You can also register deserializer here instead of annotation in Car.java

* Jsonb jsonb = JsonbBuilder.create(new JsonbConfig().withDeserializers(new

* CarDeserializer()));

Garage garage_1 = jsonb.fromJson(new FileReader(new File("garage-1.json")), Garage.class);

System.out.println(garage_1.getCar());

Garage garage_2 = jsonb.fromJson(new FileReader(new File("garage-2.json")), Garage.class);

System.out.println(garage_2.getCar());

}

Driving Honda!
Driving Tesla!

1 2	Driving Honda! Driving Tesla!

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Jackson vs. Gson vs. JSON-B | Java JSON Polymorphic type handling

Polymorphic JSON bound POJOs

Test JSON

Jackson

GSON

JSON-B

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