Retrofit 2.0 how to get deserialised error response.body

I currently use a very easy implementation, which does not require to use converters or special classes. The code I use is the following:

public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
    DialogHelper.dismiss();

    if (response.isSuccessful()) {
        // Do your success stuff...
    } else {
        try {
            JSONObject jObjError = new JSONObject(response.errorBody().string());
            Toast.makeText(getContext(), jObjError.getJSONObject("error").getString("message"), Toast.LENGTH_LONG).show();
        } catch (Exception e) {
            Toast.makeText(getContext(), e.getMessage(), Toast.LENGTH_LONG).show();
        }
    }
}

A point to note here is that response.errorBody().string() will return the correct value only once. If you call it again, it will return an empty string. So in case you want to reuse it, store the value in a variable with the first call.

There is a way to get the error body string from the response without making it empty on the next call, by rolling your own implementation of toString() that does not update the errorBody Buffer’s read-pointer.
See this answer for more info.