C# How to export DataTable to Excel solution

using System; 
using NPOI.HSSF; 
using NPOI.HPSF; 
using NPOI.HSSF.UserModel; 
using NPOI.HSSF.Util; 
using NPOI.SS.UserModel; 
using System.Collections; 
using System.IO; 
using System.Data; 
namespace BackupAttach 
{ 
public class Excel 
{ 
private HSSFWorkbook _workBook; 
private ISheet _wbSheet = null; 
private DataColumnCollection _columns = null; 
private int _col = 0; //total columns 
private int _row = 0; //total rows 
private int _sheet = 0; //total sheets 
private int _sheetRowNum = 65536; //each sheet allow rows 
public Excel() 
{ 
InstanceWorkBook(); 
} 
/// <summary> 
/// 实例方法 
/// </summary> 
/// <param name="sheetRowNum">单个表单允许的最大行数</param> 
public Excel(int sheetRowNum) 
{ 
_sheetRowNum = sheetRowNum; 
InstanceWorkBook(); 
} 
/// <summary> 
/// 实例方法 
/// </summary> 
/// <param name="columns">表头</param> 
public Excel(DataColumnCollection columns) 
{ 
_columns = columns; 
InstanceWorkBook(); 
} 
private void InstanceWorkBook() 
{ 
/////cretate WorkBook 
_workBook = new HSSFWorkbook(); 
var dsi = PropertySetFactory.CreateDocumentSummaryInformation(); 
dsi.Company = "BaiyiTimes"; 
_workBook.DocumentSummaryInformation = dsi; 
////create a entry of SummaryInformation 
var si = PropertySetFactory.CreateSummaryInformation(); 
si.Subject = "Etimes Secure Document System Log Backup"; 
_workBook.SummaryInformation = si; 
} 
private DataColumnCollection GetColumns(DataColumnCollection columns) 
{ 
return columns == null || columns.Count == 0 ? _columns : columns; 
} 
private ISheet GetSheet(ISheet sheet) 
{ 
return sheet == null ? _wbSheet : sheet; 
} 
private void CreateHeader(ISheet sheet, DataColumnCollection columns) 
{ 
_columns = GetColumns(columns); 
/////create row of column 
var oRow = sheet.CreateRow(0); 
foreach (DataColumn column in _columns) 
{ 
var oCell = oRow.CreateCell(_col); 
var style1 = _workBook.CreateCellStyle(); 
style1.FillForegroundColor = HSSFColor.BLUE.index2; 
style1.FillPattern = FillPatternType.SOLID_FOREGROUND; 
style1.Alignment = HorizontalAlignment.CENTER; 
style1.VerticalAlignment = VerticalAlignment.CENTER; 
var font = _workBook.CreateFont(); 
font.Color = HSSFColor.WHITE.index; 
style1.SetFont(font); 
oCell.CellStyle = style1; 
var name = column.ColumnName; 
oCell.SetCellValue(name.ToString()); 
_col++; 
} 
///// header belong to rows 
_row++; 
} 
private void CreateHeader(ISheet sheet) 
{ 
CreateHeader(sheet, null); 
} 
public ISheet CreateSheet() 
{ 
return CreateSheet(null); 
} 
public ISheet CreateSheet(DataColumnCollection columns) 
{ 
_wbSheet = _workBook.CreateSheet((_sheet + 1).ToString()); 
CreateHeader(_wbSheet, columns); 
_sheet++; 
return _wbSheet; 
} 
public void SetRowValue(DataRowCollection rows, ISheet sheet) 
{ 
_wbSheet = GetSheet(sheet); 
foreach (DataRow row in rows) 
{ 
SetRowValue(row); 
} 
} 
public void SetRowValue(DataRowCollection rows) 
{ 
SetRowValue(rows, null); 
} 
public void SetRowValue(DataRow row) 
{ 
// create a new sheet 
if (_row % _sheetRowNum == 0) 
{ 
CreateSheet(); 
} 
var oRow = _wbSheet.CreateRow(_row % _sheetRowNum); 
var obj = string.Empty; 
var cell = 0; 
foreach (DataColumn column in _columns) 
{ 
obj = row[column.ColumnName].ToString(); 
oRow.CreateCell(cell).SetCellValue(obj); 
cell++; 
} 
_row++; 
} 
public void SetProtectPassword(string password, string username) 
{ 
_workBook.WriteProtectWorkbook(password, username); 
} 
public void SaveAs(string filePath) 
{ 
if (File.Exists(filePath)) File.Delete(filePath); 
var file = new FileStream(filePath, FileMode.Create); 
_workBook.Write(file); 
file.Close(); 
} 
} 
}

public void DataTableToExcel(DataTable dt,string path) 
{ 
//instance excel object 
//Excel excel = new Excel(65536); 
Excel excel = new Excel(); 
//create a sheet 
excel.CreateSheet(dt.Columns); 
//write value into rows 
//excel.SetRowValue(dt.Rows); 
foreach (DataRow row in dt.Rows) 
{ 
excel.SetRowValue(row); 
} 
// set excel protected 
excel.SetProtectPassword("etimes2011@", "baiyi"); 
// save excel file to local 
excel.SaveAs(path); 
}