单例模式   LAZY:

    interface IDatabase
    {
        int GetConnection(string name);
    }

    class FileDatabase : IDatabase
    {

        private Dictionary<string, int> dic = new Dictionary<string, int>();
        private FileDatabase()
        {
            count++;
            Console.WriteLine("Read text.");
            dic = File.ReadAllLines("Demo.txt").Batch(2).ToDictionary(
                 list => list.ElementAt(0).Trim(),
                 list => int.Parse(list.ElementAt(1).Trim())
                );
        }
        public int GetConnection(string name)
        {
            return dic[name];
        }
        public int GetDictionaryCount()
        {
            return dic.Count;
        } 

        private static Lazy database = new(() => { Console.WriteLine("Load...");return new FileDatabase(); });
        public static FileDatabase Instance => database.Value;

        private static int count;
        public static int Count => count;
    }