最近，由于公司项目中需要将系统内用户操作的所有日志进行转存备份，考虑到以后可能还需要还原，所以最后决定将日志数据备份到Excel中。

下面是我项目当中Excel.cs这个类的全部代码，通过这个类可以很容易地将DataTable中的数据导入到Excel方法中。

首先，必须要下载NPOI.dll这个程序集，
类代码如下：
复制代码 代码如下:
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();
}
}
}

下面给出小Demo共参考：
复制代码 代码如下:
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);
}

缺点：如果要导入到Excel中的数据量较多时（几十万或者几百万行），全部一次性放到DataTable中可能会对内存消耗很大，建议每次导入的数据最好不要超过1000条，可采取分页查询的方式将数据导入Excel中。

优点：1997-2003版本的xls中每个表单最大只支持65536行，2010可以支持1048576行，考虑到客户机上安装的版本不一样，故Excel对象每个表单最大支持65536行，当表单到达最大行数时，Excel对象内部会自动创建新表单，在往Excel中写数据的时候不用考虑这一点，这样调用的时候更为方便