Serializing list

As we saw in the previous tutorial serializing and deserializing classes with generic types is non trivial since generic type information is lost while serializing. Gson provides a class called com.google.gson.reflect.TypeToken to store generic types. The example below shows how to use the TypeToken class to serialize and deserialize Classes with generic types.

package com.studytrails.json.gson;

import java.lang.reflect.Type;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class GenericTypesExample8 {
	public static void main(String[] args) {
		// create an animal class that is of type dog.
		Animal animal = new Animal<Dog>();
		// Create a Dog instance
		Dog dog = new Dog("I am a dog");

		animal.setAnimal(dog);
		Gson gson = new Gson();
		// Define a Type that is an Animal of type dog.
		Type animalType = new TypeToken<Animal<Dog>>() {
		}.getType();

		// we first convert the animal object to a json and then read the json
		// back. However we define the json to be of Animal type
		Animal animal1 = gson.fromJson(gson.toJson(animal, animalType), Animal.class);
		System.out.println(animal1.get().getClass()); // prints class
														// com.google.gson.internal.LinkedTreeMap

		// In contrast to above where we read the json back using the Animal
		// type, here we read the json back as the custom animalType Type. This
		// gives Gson an idea of what
		// the generic type should be.
		Animal animal2 = gson.fromJson(gson.toJson(animal), animalType);
		System.out.println(animal2.get().getClass());
		// prints class com.studytrails.json.gson.Dog

	}
}

		
		
		

Animal class

package com.studytrails.json.gson;

public class Animal {

	public T animal;

	public void setAnimal(T animal) {
		this.animal = animal;
	}

	public T get() {
		return animal;
	}

}

		
		
		

Dog Class

package com.studytrails.json.gson;

public class Dog {
	private String name;

	public Dog(String name) {
		this.name = name;
	}

	public String getName() {
		return name;
	}

}