Retrofit Expected BEGIN_ARRAY but was BEGIN_OBJECT exception

Question

I know there's a few similar question but none of them match to my problem. I have JSON response from server that looks like this :

{
  "data": {
    "list": {
      "beacons": [
        {
          "id": 56,
          "beacon_id": "56",
          "bridge_id": null,
          "mesh_id": null,
          "name": "Test beacon wcx",
          "location": "test",
          "mac_address": "e6:f5:8a:94:b8:c7",
          "firmware": "1.1",
          "pcb_revision": "2.0",
          "battery_level": null,
          "password": "0000",
          "ib": {
            "turn_on": "1",
            "major": "300",
            "minor": "10",
            "tx_power": "4",
            "interval": "400",
            "uuid": "dae19960-18ea-11e5-8ff0-0002a5d5c521",
            "secure_uuid": "0"
          },
          "euid": {
            "turn_on": "0",
            "namespace": null,
            "instance": null,
            "tx_power": null,
            "interval": null
          },
          "eeid": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null
          },
          "eurl": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null,
            "url": null
          },
          "etlm": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null
          }
        },
        {
          "id": 57,
          "beacon_id": "57",
          "bridge_id": "13",
          "mesh_id": "278",
          "name": "Marta B",
          "location": "lk",
          "mac_address": "e1:4b:64:c3:80:e2",
          "firmware": "2.1",
          "pcb_revision": "2.0",
          "battery_level": "97",
          "password": "0000",
          "ib": {
            "turn_on": "1",
            "major": "300",
            "minor": "6",
            "tx_power": "0",
            "interval": "0",
            "uuid": "dae19960-18ea-11e5-8ff0-0002a5d5c521",
            "secure_uuid": "0"
          },
          "euid": {
            "turn_on": "0",
            "namespace": null,
            "instance": null,
            "tx_power": null,
            "interval": null
          },
          "eeid": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null
          },
          "eurl": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null,
            "url": null
          },
          "etlm": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null
          }
        },
        {
          "id": 58,
          "beacon_id": "58",
          "bridge_id": null,
          "mesh_id": null,
          "name": "Marta C",
          "location": "abcdlk",
          "mac_address": "3c:cf:82:8a:e7:fe",
          "firmware": "2.1",
          "pcb_revision": "2.0",
          "battery_level": "99",
          "password": "0000",
          "ib": {
            "turn_on": "1",
            "major": "300",
            "minor": "39",
            "tx_power": "7",
            "interval": "400",
            "uuid": "dae19960-18ea-11e5-8ff0-0002a5d5c521",
            "secure_uuid": "0"
          },
          "euid": {
            "turn_on": "0",
            "namespace": null,
            "instance": null,
            "tx_power": null,
            "interval": null
          },
          "eeid": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null
          },
          "eurl": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null,
            "url": null
          },
          "etlm": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null
          }
        }
      ],
      "bridges": [
        {
          "id": 13,
          "name": "Test bridge wcx",
          "location": "netizens",
          "mac_address": "c9:1d:76:cc:a7:ca",
          "ib": {
            "turn_on": 1,
            "major": "100",
            "minor": "102",
            "tx_power": "6",
            "interval": "400",
            "uuid": "dae19960-18ea-11e5-8ff0-0002a5d5c521",
            "secure_uuid": 0
          },
          "euid": {
            "turn_on": "0",
            "namespace": null,
            "instance": null,
            "tx_power": null,
            "interval": null
          },
          "eeid": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null
          },
          "eurl": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null,
            "url": null
          },
          "etlm": {
            "turn_on": "0",
            "tx_power": null,
            "interval": null
          }
        }
      ]
    }
  },
  "ver": 1,
  "time": 1475576646,
  "status": 1,
  "status_msg": ""
}

My model class looks like this :

public class BeaconResponse {
@Expose
public DataBeacon dataBeacon;
@Expose
public int ver;
@Expose
public long time;
@Expose
public int status;
@Expose
public String status_msg;

DataBeacon has list of Beacons and Bridges objects :

@Table(name = "dataBeacon", id = "_id")

public class DataBeacon extends Model {
@Column(name = "beacon",onUpdate = Column.ForeignKeyAction.CASCADE, onDelete = Column.ForeignKeyAction.CASCADE)
public List<BeaconsModel> beacons;
@Column(name = "bridge",onUpdate = Column.ForeignKeyAction.CASCADE, onDelete = Column.ForeignKeyAction.CASCADE)
public List<BridgeModel> bridges;

}

Here's my interface for getting json :

@GET("/api/mobile/{language}/{apiVersion}/beacons/list")
    void beaconsList(Callback<BasicResponse<BeaconsListResponse>> callback);

public class BeaconsListResponse {
    @Expose
    public List<BeaconResponse> list;
}

Everything , in my opinion, should work correctly, but I'm still getting exception: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 18 path $.data.list. I don't know why - structure of the model should be correct .

Aram Tchekrekjian · Accepted Answer · 2016-10-05 20:17:33Z

Your model does not match the JSON response, the JSON response is returning an object , however your model is expecting a list, hence the error.

I think you should redesign your models as the following:

public class BeaconResponse
{
    private Data data;
    public int ver;
    public long time;
    public int status;
    public String status_msg;
}

public class Data
{
    private List list;
}

public class List
{
    private Beacons[] beacons;
    private Bridges[] bridges;
}

Then you should update your retrofit interface to expect the BeaconResponse instead of BeaconListResponse

void beaconsList(Callback<BasicResponse<BeaconsResponse>> callback);

Please note I didn't provide a full detailed model, just wanted to explain how you should match your model to the JSON reponse. Just proceed with adding your model details to be able to test your app, and let us know if it works.

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