如何从Firebase中检索android用户数据

FirebaseFirestore db = FirebaseFirestore.getInstance();

db.collection("users")
    .get()
    .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {
            if (task.isSuccessful()) {
                for (QueryDocumentSnapshot document : task.getResult()) {
                    Log.d(TAG, document.getId() + " => " + document.getData());
                }
            } else {
                Log.w(TAG, "Error getting documents.", task.getException());
            }
        }
    });

db.collection("users")
    .whereGreaterThanOrEqualTo("age", 18)
    .get()
    .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        // ...
    });