（C#）使用NPOI导出Excel

　　在做业务型的软件时，经常需要将某些数据导出，本文介绍了在Winform或Asp.net中使用NPOI（POI 项目的 .NET 版本）来操作Excel文件，而无需安装Office。

　　首先，需要获取NPOI组件。

　　其次，让你的网站或类库添加NPOI引用。对于导出导入Excel来说，需要引用的dll文件有：

　　NPOI.dll，NPOI.HSSF.dll，NPOI.POIFS.dll

　　最后，在网站或类库中新建一个导出帮助类，例如命名为ExcelHelper.cs

ExcelHelper.cs

public class ExportHelper
    {
        public static Stream RenderDataTableToExcel(DataTable SourceTable)
        {
            HSSFWorkbook workbook = new HSSFWorkbook();
            MemoryStream ms = new MemoryStream();
            HSSFSheet sheet = workbook.CreateSheet();
            HSSFRow headerRow = sheet.CreateRow(0);

            // handling header. 
            foreach (DataColumn column in SourceTable.Columns)
                headerRow.CreateCell(column.Ordinal).SetCellValue(column.ColumnName);

            // handling value. 
            int rowIndex = 1;

            foreach (DataRow row in SourceTable.Rows)
            {
                HSSFRow dataRow = sheet.CreateRow(rowIndex);

                foreach (DataColumn column in SourceTable.Columns)
                {
                    dataRow.CreateCell(column.Ordinal).SetCellValue(row[column].ToString());
                }

                rowIndex++;
            }

            workbook.Write(ms);
            ms.Flush();
            ms.Position = 0;

            sheet = null;
            headerRow = null;
            workbook = null;

            return ms;
        }
        public static DataTable RenderDataTableFromExcel(Stream ExcelFileStream, int SheetIndex, int HeaderRowIndex)
        {
            HSSFWorkbook workbook = new HSSFWorkbook(ExcelFileStream);
            HSSFSheet sheet = workbook.GetSheetAt(SheetIndex);

            DataTable table = new DataTable();

            HSSFRow headerRow = sheet.GetRow(HeaderRowIndex);
            int cellCount = headerRow.LastCellNum;

            for (int i = headerRow.FirstCellNum; i < cellCount; i++)
            {
                DataColumn column = new DataColumn(headerRow.GetCell(i).StringCellValue);
                table.Columns.Add(column);
            }

            int rowCount = sheet.LastRowNum;

            for (int i = (sheet.FirstRowNum + 1); i <= sheet.LastRowNum; i++)
            {
                HSSFRow row = sheet.GetRow(i);
                DataRow dataRow = table.NewRow();

                for (int j = row.FirstCellNum; j < cellCount; j++)
                {
                    if (row.GetCell(j) != null)

                        dataRow[j] = row.GetCell(j).ToString();
                }

                table.Rows.Add(dataRow);
            }

            ExcelFileStream.Close();
            workbook = null;
            sheet = null;
            return table;
        }
    }

在方法中调用ExcelHelper:

　　示例1：导出Excel:

protected void exportExcelFun(){
        DataTable dt=new DataTable();
        dt=XXXXX;//Use ADO.NET to get Data from DB
        MemoryStream ms = ExportHelper.RenderDataTableToExcel(dt) as MemoryStream;
        
        /*情况1：在Asp.NET中，输出文件流，浏览器自动提示下载*/
        Response.AddHeader("Content-Disposition", string.Format("attachment; filename=download.xls"));
        Response.BinaryWrite(ms.ToArray());
        ms.Close();
        ms.Dispose();
        

        /*情况2：在Winform中，弹出SaveFileDialog，提示用户选择文件放置位置。*/
        
         string saveFileName = "";
         bool fileSaved = false;
         SaveFileDialog saveDialog = new SaveFileDialog();
         saveDialog.DefaultExt = "xls";
         saveDialog.Filter = "Excel文件|*.xls";
         saveDialog.FileName = "download";
         saveDialog.ShowDialog();
         saveFileName = saveDialog.FileName;
         if (saveFileName.IndexOf(":") < 0) return; //被点了取消
         if (saveFileName != ""){
               try{
                    FileStream fs = new FileStream(saveDialog.FileName, FileMode.Create);
                    fs.Write(ms.GetBuffer(), 0, ms.GetBuffer().Length);
                    ms.Close();
                    ms.Dispose();
                    fs.Close();
                    fileSaved = true;
                }
                catch (Exception ex){
                    fileSaved = false;
                    MessageBox.Show("导出文件时出错,文件可能正被打开！\n" + ex.Message);
                }
          }
          else{
                fileSaved = false;
          }
          GC.Collect();//强行销毁
          if (fileSaved && File.Exists(saveFileName)){
          　　　　MessageBox.Show("导出成功！", "通知");
          }
          else {
                 MessageBox.Show("导出失败！", "通知");
          }
}

　　示例2：导入Excel

protected void importExcelFun(){
    /*情况1：在Asp.net网站，一般使用asp:FileUpLoad控件(实际上是一个HTML表单.input:type=file)上传文件*/
    if(this.FileUpLoader.HasFile){
        DataTable dt=new DataTable();
　　　　　//设置第1行为标题行，从第二行开始读取数据。标题行作为DataTable表头。
        dt=ExcelHelper.RenderDataTableFromExcel(this.FileUpLoader.FileContent,0,0);
　　　　　//use dt to do something 
    }

    /*情况2：在Winform中，*/
     OpenFileDialog fileDialog = new OpenFileDialog();
     fileDialog.Filter = "Excel文件|*.xls";
     fileDialog.InitialDirectory = "E:\\";//设置默认打开路径
     if (fileDialog.ShowDialog() == DialogResult.OK){
         string fileName=fileDialog.FileName;//得到文件所在位置。
　　　　　// use c# to read Excel File as Steam.
　　　　　// use ExcelHelper for converting Stream to DataTable.
     }
}