Accessing a List in Dart/Flutter

Question

I'm new to Dart/Flutter and working on a project to parse some JSON data into a list in Dart. I've been stuck trying to access the list, Dart File # 2 -"_database.bpreading" to select entries. This may be a simple solution in Dart but I've tried many commands using Map() but to no avail. Would appreciate your help. Here are the codes:-

Dart File # 1
=============
class DatabaseFileRoutines {
  Future<String> get _localPath async {
    final directory = await getApplicationDocumentsDirectory();

    return directory.path;
  }

  Future<File> get _localFile async {
    final path = await _localPath;

    return File('$path/local_persistence.json');
  }

  Future<String> readJournals() async {
    try {
      final file = await _localFile;

      if (!file.existsSync()) {
        print("File does not exist: ${file.absolute}");
        await writeBpreading('{"bpreadings": []}');
      }
      String contents = await file.readAsString();

      return contents;
    } catch (e) {
      print("error readBpreading: $e");
      return "";
    }
  }

  Future<File> writeBpreading(String json) async {
    final file = await _localFile;
    return file.writeAsString('$json');
  }
}

Database databaseFromJson(String str) {
  final dataFromJson = json.decode(str);
  return Database.fromJson(dataFromJson);
}

String databaseToJson(Database data) {
  final dataToJson = data.toJson();
  return json.encode(dataToJson);
}

class Database {
  List<Bpreading> bpreading;

  Database({
    this.bpreading,
  });

  factory Database.fromJson(Map<String, dynamic> json) => Database(
        bpreading: List<Bpreading>.from(
            json["journals"].map((x) => Bpreading.fromJson(x))),
      );

  Map<String, dynamic> toJson() => {
        "journals": List<dynamic>.from(bpreading.map((x) => x.toJson())),
      };
}

class Bpreading {
  String id;
  String date;
  String time;
  String lab1;
  String lab2;

  Bpreading({
    this.id,
    this.date,
    this.time,
    this.lab1,
    this.lab2,
  });

 

  factory Bpreading.fromJson(Map<String, dynamic> json) => Bpreading(
        id: json["id"],
        date: json["date"],
        time: json["time"],
        lab1: json["lab1"],
        lab2: json["lab2"],
      );

  Map<String, dynamic> toJson() => {
        "id": id,
        "date": date,
        "time": time,
        "lab1": lab1,
        "lab2": lab2,
      };
}
Dart file #2
============
class BpJournal extends StatefulWidget {
   
   @override
   BpJournalState createState() => BpJournalState();
}

class BpJournalState extends State<BpJournal> {
  Database _database;
  String dia;

  Future<List<Bpreading>> _loadJournals() async {
     await DatabaseFileRoutines().readJournals().then((journalsJson) {
       _database = databaseFromJson(journalsJson);
       _database.bpreading.sort((comp1, comp2) => comp2.date.compareTo(comp1.date));
     });
     return _database.bpreading;
  }