Gson Type Adapter vs. Custom Deseralizer

Question

The example below shows a class (Club) that contains a collection of an abstract class (Member). I\'m confused as to whether I need a TypeAdapter or JsonDeserializer to make

Answer 1

Ok, real working example (I'm pretty sure this time).

The Club

package gson.test;
import java.util.ArrayList;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

public class Club {
    public static void main(String[] args) {
        // Setup a Club with 2 members
        Club myClub = new Club();
        myClub.addMember(new Silver("Jack"));
        myClub.addMember(new Gold("Jill"));
        myClub.addMember(new Silver("Mike"));

        // Get the GSON Object and register Type Adapter
        GsonBuilder builder = new GsonBuilder();
        builder.registerTypeAdapter(Member.class, new MemberDeserializer());
        builder.registerTypeAdapter(Member.class, new MemberSerializer());
        builder.setPrettyPrinting();
        Gson gson = builder.create();

        // Serialize Club to JSON
        String myJsonClub = gson.toJson(myClub); 

        // De-Serialize to Club
        Club myNewClub = gson.fromJson(myJsonClub, Club.class);
        System.out.println(myClub.equals(myNewClub) ? "Cloned!" : "Failed");
        System.out.println(gson.toJson(myNewClub));
    }

    private String title = "MyClub";
    private ArrayList members = new ArrayList();

    public boolean equals(Object club) {
        Club that = (Club) club;
        if (!this.title.equals(that.title)) return false;
        for (int i=0; i

The Member Abstract Class

package gson.test;
public abstract class Member {
    private String clsname = this.getClass().getName() ;
    private int type;
    private String name = "unknown";

    public Member() { }
    public Member(String theName) {this.name = theName;}
    public int getType() { return type; }
    public void setType(int type) { this.type = type; }
    public boolean equals(Object member) {
        Member that = (Member) member;
        return this.name.equals(that.name);
    }
}

The Concrete Sub-Classes Silver and Gold

package gson.test;
public class Silver extends Member {
    private String silverData = "SomeSilverData";
    public Silver() { 
        super(); 
        this.setType(1); 
    }
    public Silver(String theName) {
        super(theName); 
        this.setType(1); 
    }
    public boolean equals(Object that) {
        Silver silver = (Silver)that;
        return (super.equals(that) && this.silverData.equals(silver.silverData)); 
    }
}

package gson.test;
public class Gold extends Member {
    private String goldData = "SomeGoldData";
    private String extraData = "Extra Gold Data";
    public Gold() {
        super(); 
        this.setType(2);
    }
    public Gold(String theName) { 
        super(theName); 
        this.setType(2); 
    }
    public boolean equals(Gold that) {
        Gold gold = (Gold) that;
        return (super.equals(that) && this.goldData.equals(gold.goldData)); 
    }
}

The Custom Member Serailizer

package gson.test;
import java.lang.reflect.Type;
import com.google.gson.JsonElement;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

public class MemberSerializer implements JsonSerializer {

    public JsonElement serialize(Member src, Type member, JsonSerializationContext context) {
        switch (src.getType()) {
            case 1: return context.serialize((Silver)src);
            case 2: return context.serialize((Gold)src);
            default: return null;
        }
    }
}

The custom Deserializer

package gson.test;
import java.lang.reflect.Type;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;

public class MemberDeserializer implements JsonDeserializer {
    @Override
    public Member deserialize(JsonElement json, Type member, JsonDeserializationContext context) {
        int myType = json.getAsJsonObject().get("type").getAsInt();
        switch (myType) {
            case 1: return context.deserialize(json, Silver.class);
            case 2: return context.deserialize(json, Gold.class);
            default: return null;
        }
    }
}

And... the output

Cloned!
{
  "title": "MyClub",
  "members": [
    {
      "silverData": "SomeSilverData",
      "clsname": "gson.test.Silver",
      "type": 1,
      "name": "Jack"
    },
    {
      "goldData": "SomeGoldData",
      "extraData": "Extra Gold Data",
      "clsname": "gson.test.Gold",
      "type": 2,
      "name": "Jill"
    },
    {
      "silverData": "SomeSilverData",
      "clsname": "gson.test.Silver",
      "type": 1,
      "name": "Mike"
    }
  ]
}

I should note that my real use-case is one where performance should not be an issue, I'm loading a cache of objects from jSon text files so the frequency with this code is executed makes performance much less important than maintainability.