Retrofit:2.0.0-beta2 http call and response handling - retrofit

Question

My backend returns this json object to signal a succesful new user registration
{
"error": false,
"message": "You have been successfully registered"
}
and this to signal the account already exists
{
"error": true,
"message": "Sorry, this email already exists"
}
and this on other registration failure
{
"error": true,
"message": "An error occurred!! Please try again"
}
I want to use retrofit:2.0.0-beta2 to make an asynchronous http call and handle the response to take the use to the home page or redirect to the login page accordingly.
Here's my POJO:
public class User {
public final String email, firstname, lastname, city, birthday, gender, password;
public User(final String email, final String firstname, final String lastname,
final String city, final String birthday, final String gender, final String password) {
this.email = email;
this.firstname = firstname;
this.lastname = lastname;
this.city = city;
this.birthday = birthday;
this.gender = gender;
this.password = password;
}
}
Here's my service:
public interface APIService {
#POST("/api/user")
Call<User> createUser(#Body User user);
}

Answer 1

You need to create a extra class to handled response.
public class ResponseApi{
public String error;
public String message;
}
You're inferface
#POST("/api/user")
Call<ResponseApi> createUser(#Body User user);

Answer 2

You need to implement onResponse listener and handle the redirects or any other action inside it.
For example:
protected void loginAttempt(final View v) {
authUser = new HashMap<>();
authUser.put("email", email.getText().toString());
authUser.put("password", password.getText().toString());
Call call = SubApplication.api.authUser(authUser);
call.enqueue(new Callback() {
#Override
public void onResponse(Call call, Response response) {
try {
JSONObject responseObject = new JSONObject(new Gson().toJson(response.body()));
Log.d("LoginActivity", "onResponse: " + responseObject.toString());
if (responseObject.getBoolean("success") == true) {
Toast.makeText(v.getContext(), getString(R.string.error_login_success), Toast.LENGTH_LONG).show();
Intent intent = new Intent(v.getContext(), DashboardActivity.class);
startActivity(intent);
finish();
} else {
Toast.makeText(v.getContext(), getString(R.string.error_login_failed), Toast.LENGTH_LONG).show();
}
} catch (Exception e) {
Log.e("LoginActivity", "Exception: " + e);
Toast.makeText(v.getContext(), getString(R.string.error_login_failed), Toast.LENGTH_LONG).show();
}
}
#Override
public void onFailure(Call call, Throwable t) {
Log.e("LoginActivity", "onFailure: " + t);
}
});