Gson with abstract elements

EntityAdapter.java

package model.entities;

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import java.lang.reflect.Type;

/**
 *
 * @author gillesbraun
 */
public class EntityAdapter implements JsonSerializer<Entity>, JsonDeserializer<Entity> {

    @Override
    public JsonElement serialize(Entity t, Type type, JsonSerializationContext jsc) {
        JsonObject result = new JsonObject();
        result.add("type", new JsonPrimitive(t.getClass().getSimpleName()));
        result.add("properties", jsc.serialize(t, t.getClass()));
        return result;
    }

    @Override
    public Entity deserialize(JsonElement je, Type typeOfT, JsonDeserializationContext jdc) throws JsonParseException {
        JsonObject jsonObject = je.getAsJsonObject();
        String type = jsonObject.get("type").getAsString();
        JsonElement element = jsonObject.get("properties");
        
        try {
            return jdc.deserialize(element, Class.forName("model.entities."+type));
        } catch (ClassNotFoundException ex) {
            throw new JsonParseException("Unknown element type: "+type, ex);
        }
    }
    
}

Simulator.java

public class Simulator {
    private Cells readState, writeState;
    
    public void saveToFile(String file) throws IOException {
        GsonBuilder gsonBuilder = new GsonBuilder();
        gsonBuilder.registerTypeAdapter(Entity.class, new EntityAdapter());
        Gson gson = gsonBuilder.create();
        String json = gson.toJson(readState);

        try (PrintWriter pw = new PrintWriter(new FileWriter(file))) {
            pw.print(json);
        }
    }

    public void loadFromFile(String file) throws FileNotFoundException, IOException {
        String l = null, json = "";
        BufferedReader br = new BufferedReader(new FileReader(file));
        while((l = br.readLine()) != null) {
            json += l;
        }
        br.close();
        GsonBuilder gsonBuilder = new GsonBuilder();
        gsonBuilder.registerTypeAdapter(Entity.class, new EntityAdapter());
        Gson gson = gsonBuilder.create();
        readState = gson.fromJson(json, Cells.class);
    }
}