Deserializing ArrayList<Interface> using GSON

Question

I have a class Shop

public class Shop {

  private String name;
  private ArrayList<Fruitable> fruits;


  public String toJson() {
     Gson gson = new Gson();
     return gson.toJson(this, Shop.class) 
  }   

}

Apple and Orange are the two classes that implements Fruitable interface.

Fruitable:

public interface Fruitable {
   String getColor();
}

Apple:

public class Apple implements Fruitable {

 private int Id;     

 @Override
 public String getColor() {
    return "red";
  }

 }

Orange:

 public class Orange implements Fruitable {

 private int Id;

 @Override
 public String getColor() {
    return "orange";
  }

 }

I can serialize Shop using GSON, however, I cannot deserialize it properly.

When I deserialize, the ArrayList<Fruitable> has objects, but the objects are null.

This is because GSON requires a concrete instance to deserialze into.

I know I can implement JsonDeserializer in Shop.

However, can I implement some deserializing mechanism, inside Apple and Orange so they will deserialize themselves?

If that is not possible, and I have to write a deserializer in Shop, can I write code just to deserialize the fruits property and not the other properties,i.e. GSON will deserialize the remaining properties assuming they are concrete instances?

Answer 1

Ok so you should use GSON annotations they will make your life a whole lot easier. An example:

public class Deal{

   @SerializedName("name")
   String name;

   @SerializedName("times")
   List<DealTime> times;

}

The json coming back will roughly look this:

{
   name:dave,
   times[
     {
      end:400,
      start:200
     },
     {
      end:30,
      start:500
     }
   ]
}

Then your DealTime class will have the following:

   public class DealTime{

       @SerializedName("end")
       int end;

       @SerializedName("start")
       int start;

    }

All you have to do is cast the json coming back with GSON using the Deal object. Hope this helps.