NPOI 简单应用

　　     public void CreateExcel()
        {
            XSSFWorkbook workbook = new XSSFWorkbook();
            ISheet sheet = workbook.CreateSheet("sheet1");

            int iColumnNo = 20;

            IRow rowHeader = sheet.CreateRow(0);
            for(int i=0;i<iColumnNo;i++)
            {
                ICell cell = rowHeader.CreateCell(i);
                cell.SetCellValue("ColumnName_" + i);
            }
            
            IRow row = sheet.CreateRow(1);     
            for(int i=0;i<iColumnNo;i++)
            {
                ICell cell = row.CreateCell(i);
                cell.SetCellValue("cellvalue_"+i);
            }

            using(FileStream fs=new FileStream(@"D:\CreateExcel_Npoi.xlsx",FileMode.OpenOrCreate))
            {
                workbook.Write(fs);
            }
        }

        public void ReadExcel()
        {
            StringBuilder sbContent = new StringBuilder();

            string strExcelPath = @"D:\CreateExcel_Npoi.xlsx";

            using(FileStream fs=new FileStream(strExcelPath,FileMode.Open))
            {
                XSSFWorkbook workbook = new XSSFWorkbook(fs);

                for(int i=0;i<workbook.NumberOfSheets;i++)
                {
                    sbContent.AppendLine(workbook.GetSheetName(i));

                    ISheet sheet = workbook.GetSheetAt(i);
                    for(int j=0;j<=sheet.LastRowNum;j++)
                    {
                        IRow row=sheet.GetRow(j);
                        for(int k=0;k<row.LastCellNum;k++)
                        {
                            ICell cell = row.GetCell(k);
                            if(cell!=null)
                            {
                                sbContent.Append(cell.ToString() + " ");
                            }  
                        }
                    }
                    sbContent.AppendLine();
                }
            }
            using (StreamWriter sw = new StreamWriter(@"D:\ExcelNpoi.txt"))
            {
                sw.Write(sbContent.ToString());
                sw.Flush();
            }
        }

        public void UpdateExcel()
        {
            string strExcelPath = @"D:\CreateExcel_Npoi.xlsx";

            XSSFWorkbook workbook;
            using (FileStream fs = new FileStream(strExcelPath, FileMode.Open))
            {
                workbook = new XSSFWorkbook(fs);
                ISheet sheet = workbook.GetSheetAt(0);

                IRow row = sheet.GetRow(0);
                ICell cell = row.GetCell(0);

                string strCellValueNew = "UpdateExcel_SetCellNewValue";
                cell.SetCellValue(strCellValueNew);
            }

            string strExcelPathNew= @"D:\CreateExcel_Npoi_New.xlsx";
            using(FileStream fs=File.OpenWrite(strExcelPathNew))
            {
                workbook.Write(fs);
            }
        }