序列化的 object 中包含的每个 object 是否也必须序列化？ （安卓、爪哇）

Question

I am working on Android Studio (Java), and have incorporated Google Firebase into my project. In my main activity, I instantiate a firebase user, and store all the relevant information in a custom "User" class.

public class User implements Serializable{
    FirebaseUser user;
    FirebaseAuth mAuth;
    String uid;

    public User()
    {
        System.out.println("Creating User");
        mAuth = FirebaseAuth.getInstance(); 
        user = mAuth.getCurrentUser();
        uid = user.getUid();
    }

}

I have a multi tab setup, where each tab is a fragment. Each fragment needs access to the lone user object representing the currently signed in user, so I pass the User object to each fragment. In order to do that, it needs to be serialized, which it is. Here is one of the fragments:

public class tab_list extends Fragment {

     private static final String ARG_PARAM1 = "user_List";
     private User user;

    public tab_list() {
        // Required empty public constructor
    }

    public static tab_list newInstance(User u) {
        tab_list fragment = new tab_list(); // This calls the empty constructor above
        Bundle args = new Bundle();
        args.putSerializable(ARG_PARAM1, u);
        fragment.setArguments(args);
        return fragment;
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            user = (User) getArguments().getSerializable(ARG_PARAM1);
        }
    }
    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState){
       //Do Stuff
    }
}

Everything works great, The tab has access to the data stored in user, and I can do everything I need too. until the app ends up in the background, If my phone puts the app into the background, either by switching apps or pulling down the tray or letting the screen sleep: the app crashes and I get this error:

"Parcelable encountered IOException writing serializable object". . . Caused by: java.io.NotSerializableException: com.google.firebase.auth.internal.zzn

To me, this implies that the parts of firebase auth ALSO need to be serialized. Is this the correct interpretation? I feel like this is going to be a long rabbit hole of serialization if that is the case, if it is even possible to serialize classes I don't control (and don't want to alter). Is there a way around this? What is the proper way to do this?

Thank you for your time.

Answer 1

To me, this implies that the parts of firebase auth ALSO need to be serialized. Is this the correct interpretation?

Yes, if you want to serialize something with Java's built-in serialization, it will attempt to serialize all nested objects. As you're discovering, that's not really so easy with Firebase objects. They are simply not meant to be serialized this way.

Your data objects to be serialized should ideally contain only the most basic, raw data. They should not contain more complex objects (especially those that are not themselves implementing Serializable ). There is really no need to serialize FirebaseAuth, as that's a singleton. And you for FirebaseUser, you should consider pulling out only the relevant data from that object.

Answer 2

Fields declared as transient are not serialized by the default serialization mechanism.

Language spec, 8.3.1.3

Serializable interface

I would suppose you can therefore make the FirebaseUser and FirebaseAuth members transient, while 'manually' extracting any parts of them you need.