How parse json array with multiple objects by gson?

Question

How can I parse json using gson? I have a json array with multiple object types, and I don't know, what kind of object I need to create to save this structure. I cannot change the json data format (I don't control the server). Can I use gson or other library parse this json array, how should I do?

This is the json code block:

[
  {
    "type": 1,
    "object": {
      "title1": "title1",
      "title2": "title2"
    }
  },
  {
    "type": 2,
    "object": [
      "string",
      "string",
      "string"
    ]
  },
  {
    "type": 3,
    "object": [
      {
        "url": "url",
        "text": "text",
        "width": 600,
        "height": 600
      },
      {
        "url": "url",
        "text": "text",
        "width": 600,
        "height": 600
      }
    ]
  },
  {
    "type": 4,
    "object": {
      "id": 337203,
      "type": 1,
      "city": "1"
    }
  }
]

Answer 1

This json structure is inherently gson-unfriendly. i.e You cannot model this cleanly in java because the "object" key refers to a dynamic type. The best you can do with this structure is model it like so:

    public class Models extends ArrayList<Models.Container> {

    public class Container {
        public int type;
        public Object object;
    }

    public class Type1Object {
        public String title1;
        public String title2;
    }

    public class Type3Object {
        public String url;
        public String text;
        public int width;
        public int height;
    }

    public class Type4Object {
        public int id;
        public int type;
        public int city;
    }

}

Then do some awkward switch on type and the object field:

String json = "{ ... json string ... }";
Gson gson = new Gson();
Models model = gson.fromJson(json, Models.class);


for (Models.Container container : model) {

    String innerJson = gson.toJson(container.object);

    switch(container.type){
        case 1:
            Models.Type1Object type1Object = gson.fromJson(innerJson, Models.Type1Object.class);
            // do something with type 1 object...                                
            break;
        case 2:
            String[] type2Object = gson.fromJson(innerJson, String[].class);
            // do something with type 2 object...
            break;
        case 3:
            Models.Type3Object[] type3Object = gson.fromJson(innerJson, Models.Type3Object[].class);
            // do something with type 3 object...
            break;
        case 4:
            Models.Type4Object type4Object = gson.fromJson(innerJson, Models.Type4Object.class);
            // do something with type 4 object...
            break;

    }
}

Ultimately the best solution is to get the json structure changed to something more compatible with java.

E.g:

[
  {
    "type": 1,
    "type1Object": {
      "title1": "title1",
      "title2": "title2"
    }
  },
  {
    "type": 2,
    "type2Object": [
      "string",
      "string",
      "string"
    ]
  },
  {
    "type": 3,
    "type3Object": [
      {
        "url": "url",
        "text": "text",
        "width": 600,
        "height": 600
      },
      {
        "url": "url",
        "text": "text",
        "width": 600,
        "height": 600
      }
    ]
  },
  {
    "type": 4,
    "type4Object": {
      "id": 337203,
      "type": 1,
      "city": "1"
    }
  }
]

Answer 2

This may be a bit late for the original poster, but hopefully it will help someone else.

I am using Gson in Android. I have seen everyone use custom classes and long way round solutions. Mine is basic.

I have an ArrayList of many different Object types (Models for my database) - Profile is one of them. I get the item using mContactList.get(i) which returns:

{"profile": 
    {"name":"Josh",
     "position":"Programmer",
     "profile_id":1,
     "profile_image_id":10,
     "user_id":1472934469
    },
 "user":
    {"email":"[email protected]",
     "phone_numbers":[],
     "user_id":1,
     "user_type_id":1
    },
 "follower":
    {"follower_id":3,
     "following_date":1.4729345E9,
     "referred_by_id":2,
     "user_from_id":1,
     "user_to_id":2
    },
 "media":
    {"link":"uploads/profiles/profile-photos/originals/1-G9FSkRCzikP4QFY.png",
     "media_description":"",
     "media_id":10,
     "media_name":"",
     "media_slug":"",
     "medium_link":"uploads/profiles/profile-photos/thumbs-medium/1-G9FSkRCzikP4QFY.png",
     "thumbnail_link":"uploads/profiles/profile-photos/thumbs-small/1-G9FSkRCzikP4QFY.png",
     "uploader_id":1
    }
}

Now I create the Gson object:

Gson gson = new Gson();
// this creates the JSON string you see above with all of the objects
String str_obj = new Gson().toJson(mContactList.get(i)); 

Now instead of creating a custom class - just pass it through as a JsonObject using the following code:

JsonObject obj = gson.fromJson(str_obj, JsonObject.class);

And now, you can call the object like so:

JsonObject profile = obj.getAsJsonObject("profile");