C#でエクセルのデータをテーブル形式で取得する 自動化の基礎

private DataTable GetExcelDataBySheetName(string filepath, string sheetname)
{
    using (FileStream stream = new FileStream(filepath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
    using (var streamReader = new StreamReader(stream))
    {
        IExcelDataReader reader;
        Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);

        if (filepath.EndsWith(".xls") || filepath.EndsWith(".xlsx") || filepath.EndsWith(".xlsb"))
        {
            reader = ExcelReaderFactory.CreateReader(streamReader.BaseStream, new ExcelReaderConfiguration()
            {
                FallbackEncoding = Encoding.GetEncoding("Shift_JIS")
            });
        }
        else if (filepath.EndsWith(".csv"))
        {
            reader = ExcelReaderFactory.CreateCsvReader(streamReader.BaseStream, new ExcelReaderConfiguration()
            {
                FallbackEncoding = Encoding.GetEncoding("Shift_JIS")
            });
        }
        else
        {
            MessageBox.Show("サポート対象外の拡張子です。");
            return null;
        }

        var dataset = reader.AsDataSet();
        var worksheet = dataset.Tables[sheetname];
        reader.Close();

        return worksheet;
    }
}