@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "kind")
@JsonSubTypes({
    @JsonSubTypes.Type(value = Square.class, name = Square.JSON_TYPE_NAME),
    @JsonSubTypes.Type(value = Rectangle.class, name = Rectangle.JSON_TYPE_NAME),
    @JsonSubTypes.Type(value = Circle.class, name = Circle.JSON_TYPE_NAME),
})
private abstract class Shape {
    public final String kind;
    public Shape(String kind) {
        this.kind = kind;
    }
}
public class Square extends Shape {
    public static final String JSON_TYPE_NAME = "square";
    public double size;
    public Square() {
        super(JSON_TYPE_NAME);
    }
}
public class Rectangle extends Shape {
    public static final String JSON_TYPE_NAME = "rectangle";
    public double width;
    public double height;
    public Rectangle() {
        super(JSON_TYPE_NAME);
    }
}
public class Circle extends Shape {
    public static final String JSON_TYPE_NAME = "circle";
    public double radius;
    public Circle() {
        super(JSON_TYPE_NAME);
    }
}

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "kind")
@JsonSubTypes({
    @JsonSubTypes.Type(value = Square.class, name = "square"),
    @JsonSubTypes.Type(value = Rectangle.class, name = "rectangle"),
    @JsonSubTypes.Type(value = Circle.class, name = "circle"),
})
private abstract class Shape {
    public final String kind;
    public Shape() {
        this.kind = Utils.getJsonSubTypeName(Shape.class, this.getClass());
    }
}
public class Square extends Shape {
    public double size;
}
public class Rectangle extends Shape {
    public double width;
    public double height;
}
public class Circle extends Shape {
    public double radius;
}
public class Utils {
    public static String getJsonSubTypeName(Class<?> root, Class<?> subClass) {
        final JsonSubTypes jsonSubTypesAnnotation = root.getAnnotation(JsonSubTypes.class);
        if (jsonSubTypesAnnotation == null) {
            throw new RuntimeException(String.format(
                    "Class '%s' is not annotated with @JsonSubTypes annotation",
                    root.getName()));
        }
        for (JsonSubTypes.Type typeAnnotation : jsonSubTypesAnnotation.value()) {
            if (Objects.equal(typeAnnotation.value(), subClass)) {
                return typeAnnotation.name();
            }
        }
        throw new RuntimeException(String.format(
                "Class '%s' is not specified in @JsonSubTypes annotation of '%s' class",
                subClass.getName(), root.getName()));
    }
}