import com.google.gson.Gson;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import com.google.gson.stream.JsonReader;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class MyClass {
    public static void main(String args[]) {
        Gson gson = new Gson();
        Set<String> availableData = new HashSet<>();
        availableData.add("{\"id\":\"Id1\"}");
        availableData.add("{\"id\":\"Id2\",\"title\":\"anyTitle\"}");
        Iterator<String> itr = availableData.iterator();
        while (itr.hasNext()) {
            Data data = gson.fromJson(itr.next(), Data.class);
            System.out.println(data.id + " " + data.title);
        }
    }

    public class Data {
        public String id;
        public String title;
    }
}