Creating array list of java objects from JSON URL with Gson

Question

I am able to parse the following data into a java object:

{
    "name": "testname",
    "address": "1337 455 ftw",
    "type": "sometype",
    "notes": "cheers mate"
}

using this code:

public class Test 
{
    public static void main (String[] args) throws Exception
    {
        URL objectGet = new URL("http://10.0.0.4/file.json");

        URLConnection yc = objectGet.openConnection();
        BufferedReader in = new BufferedReader(
                new InputStreamReader(
                yc.getInputStream()));

        Gson gson = new Gson();

        try {
            DataO data = new Gson().fromJson(in, DataO.class);

            System.out.println(data.getName());
        }catch (Exception e) {
            e.printStackTrace();
        }
    }      
}

But now I want to store a list of these objects out of the following JSON String:

[
    {
        "name": "testname",
        "address": "1337 455 ftw",
        "type": "sometype",
        "notes": "cheers mate"
    },
    {
        "name": "SumYumStuff",
        "address": "no need",
        "type": "clunkdroid",
        "notes": "Very inefficient but high specs so no problem."
    }
]

Could someone help me modify my code to do this?

Answer 1

You could specify the type to deserialize into as an array or as a collection.

As Array:

import java.io.FileReader;

import com.google.gson.Gson;

public class GsonFoo
{
  public static void main(String[] args) throws Exception
  {
    Data0[] data = new Gson().fromJson(new FileReader("input.json"), Data0[].class);
    System.out.println(new Gson().toJson(data));
  }
}

class Data0
{
  String name;
  String address;
  String type;
  String notes;
}

As List:

import java.io.FileReader;
import java.util.List;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class GsonFoo
{
  public static void main(String[] args) throws Exception
  {
    List<Data0> data = new Gson().fromJson(new FileReader("input.json"), new TypeToken<List<Data0>>(){}.getType());
    System.out.println(new Gson().toJson(data));
  }
}

Answer 2

A quick look in the Gson User Guide indicates that this might not be possible since the deserializer doesn't know the type of the elements since you could have elements of different types in the array.

Collections Limitations

Can serialize collection of arbitrary objects but can not deserialize from it Because there is no way for the user to indicate the type of the resulting object While deserializing, Collection must be of a specific generic type