In the last example we persisted polymorphic type information as JSON property by using @JsonTypeInfo with include=JsonTypeInfo.As.PROPERTY. Sometime it might not be possible to persist type info as JSON property (may be there's a conflict), in that case we can persist it as a wrapper. We have two options:

WRAPPER_OBJECT

This wraps typed JSON value in a JSON Object that has a single entry, where key is serialized as type's identifier, and value is the actual JSON object.

Example:

@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.WRAPPER_OBJECT)
public abstract class Shape {
}

above will serialized as:

{"shapes":[{"com.logicbig.example.Rectangle":{"w":3,"h":6}},{"com.logicbig.example.Circle":{"radius":5}}]}

WRAPPER_ARRAY

This wraps typed JSON value in a 2-element JSON array: first element is the type's identifier, and second element is the actual JSON object.

Example:

@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.WRAPPER_ARRAY)
public abstract class Shape {
}

{"shapes":[["com.logicbig.example.Rectangle",{"w":3,"h":6}],["com.logicbig.example.Circle",{"radius":5}]]}

Complete Example

Java Objects

@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.WRAPPER_OBJECT)
public abstract class Shape {
}

public class Rectangle extends Shape {
  private int w;
  private int h;
    .............
}

public class Circle extends Shape {
  int radius;
    .............
}

public class View {
  private List<Shape> shapes;
    .............
}

Serializing/deserializing

public class ExampleMain {
  public static void main(String[] args) throws IOException {
      View v = new View();
      v.setShapes(new ArrayList<>(List.of(Rectangle.of(3, 6), Circle.of(5))));

      System.out.println("-- serializing --");
      ObjectMapper om = new ObjectMapper();
      String s = om.writeValueAsString(v);
      System.out.println(s);

      System.out.println("-- deserializing --");
      View view = om.readValue(s, View.class);
      System.out.println(view);
  }
}

-- serializing --
{"shapes":[{"com.logicbig.example.Rectangle":{"w":3,"h":6}},{"com.logicbig.example.Circle":{"radius":5}}]}
-- deserializing --
View{shapes=[Rectangle{w=3, h=6}, Circle{radius=5}]}

Example Project

Dependencies and Technologies Used:

• jackson-databind 2.9.6: General data-binding functionality for Jackson: works on core streaming API.
• JDK 10
• Maven 3.3.9