A simple POST request with GSON

{ 
    "id": "12345",
    "type": "android"
}

public class GetDeviceRequest {

    @SerializedName("deviceId")
    private String mDeviceId;

    public GetDeviceRequest(String deviceId) {
        this.mDeviceId = deviceId;
    }

    public String getDeviceId() {
        return mDeviceId;
    }

}

public interface Service {

    @POST("device")
    Call<Device> getDevice(@Body GetDeviceRequest getDeviceRequest);

}

public class RestClient {

    private static Service REST_CLIENT;

    static {
        setupRestClient();
    }

    private static void setupRestClient() {
        
        // Define gson 
        Gson gson = new Gson();

        // Define our client 
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("http://example.com/")
                .addConverterFactory(GsonConverterFactory.create(gson))
                .build();

        REST_CLIENT = retrofit.create(Service.class);
    }

    public static Retrofit getRestClient() {
        return REST_CLIENT;
    }

}

public class Device {

    @SerializedName("id")
    private String mId;

    @SerializedName("type")
    private String mType;

    public String getId() {
        return mId;
    }

    public String getType() {
        return mType;
    }

}

public class DeviceController {

    // Other initialization code here...

    public void getDeviceFromAPI() {

        // Define our request and enqueue 
        Call<Device> call = RestClient.getRestClient().getDevice(new GetDeviceRequest("12345"));

        // Go ahead and enqueue the request 
        call.enqueue(new Callback<Device>() {
            @Override
            public void onSuccess(Response<Device> deviceResponse) {
                // Take care of your device here 
                if (deviceResponse.isSuccess()) {
                    // Handle success
                    //delegate.passDeviceObject();
                }
            }

            @Override
            public void onFailure(Throwable t) {
                // Go ahead and handle the error here 
            } 

        });