Polymorphism with gson

Polymorphism with gson

Polymorphism refers to the ability of objects to take on multiple forms or types. In the context of Gson, which is a Java library for serializing and deserializing JSON data, polymorphism can be useful when you have a JSON structure that can represent different types of objects and you want to deserialize them into their corresponding Java classes.

To achieve polymorphism with Gson, you can use Gson's built-in support for handling polymorphic types. Gson provides a way to serialize and deserialize objects that inherit from a common base class or interface. Here's how you can do it:

  • Define a base class or interface that all the polymorphic objects inherit or implement. This base class or interface should contain the common properties that all the objects share.
public interface Shape { void draw(); }
  • Create concrete classes that implement the interface or inherit from the base class. These classes should define the specific properties and behaviors of each type of object.
public class Circle implements Shape { private double radius; // Constructor, getters, and setters @Override public void draw() { System.out.println("Drawing a circle."); } } public class Square implements Shape { private double sideLength; // Constructor, getters, and setters @Override public void draw() { System.out.println("Drawing a square."); } }
  • Configure Gson to handle polymorphism using the @JsonSubTypes and @JsonTypeInfo annotations on the base class or interface. This tells Gson how to identify and instantiate the correct subclass when deserializing JSON data.
import com.fasterxml.jackson.annotation.JsonSubTypes; import com.fasterxml.jackson.annotation.JsonTypeInfo; @JsonTypeInfo( use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type" ) @JsonSubTypes({ @JsonSubTypes.Type(value = Circle.class, name = "circle"), @JsonSubTypes.Type(value = Square.class, name = "square") }) public interface Shape { void draw(); }

In this example, we've used the @JsonTypeInfo annotation to specify that the "type" property in the JSON data should be used to determine the subclass to instantiate, and we've defined two subclasses, "circle" and "square."

  • Serialize and deserialize JSON data using Gson. When deserializing JSON data into objects, Gson will use the "type" property to determine which subclass to create.
Gson gson = new Gson(); // Serialize an object to JSON Circle circle = new Circle(5.0); String json = gson.toJson(circle); // Deserialize JSON to object Shape shape = gson.fromJson(json, Shape.class); shape.draw(); // This will call the draw method of the Circle class

In this example, Gson will correctly deserialize the JSON data into a Circle object because the "type" property in the JSON data indicates that it's a circle.

By following these steps and using the @JsonSubTypes and @JsonTypeInfo annotations, you can achieve polymorphism when serializing and deserializing JSON data with Gson. This allows you to work with JSON structures that represent different types of objects in a flexible and extensible way.

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