NPOI大数据分批写入同个Excel

实现过程：
要导出来的数据库数据量很大，一次取出来压力有点大，故分批取出来，导入到同一个Excel。
因为Excel2003版最大行数是65536行，Excel2007开始的版本最大行数是1048576行，故NPOI导出时候选择了Excel2007。

Form1.cs

    /* 
    引用命名空间： 
    using System.IO; 
    using System.Threading.Tasks; 
    using NPOI.HSSF.UserModel; 
    using NPOI.SS.UserModel; 
    using NPOI.XSSF.UserModel; 
    */  
            
    public Form1()  
    {  
        InitializeComponent();  
        List<DictionaryEntry> list = new List<DictionaryEntry>(){  
              new DictionaryEntry(1, "XA"),  
              new DictionaryEntry(2, "XB")  
        };  
        cbType.BindComboBox(list);                      
    }  
      
    private void CreateExcel(string fileName)  
    {  
        if (File.Exists(fileName))  
            File.Delete(fileName);  
      
        IWorkbook workbook = new XSSFWorkbook();  
        ISheet sheet = workbook.CreateSheet("Sheet1");  
        FileStream sw = File.Create(fileName);  
        workbook.Write(sw);  
        sw.Close();                     
    }  
      
      
    private void btnExport_Click(object sender, EventArgs e)  
    {              
        try  
        {  
            Task.Factory.StartNew(() =>  
            {  
                txtSql.SafeCall(() =>  
                {  
                    txtSql.AppendText("开始处理...rn");  
                });  
      
                BusinessType businessType = GetBusinessType();  
                string[] sqlWhereArray = Sql.SqlWhereArray;  
                string[] DateRemarkArray = Sql.DateRemarkArray;  
                string fileName = string.Format("{0}.xlsx", businessType.ToString());  
      
                CreateExcel(fileName);                                         
      
                string sqlCount = Sql.GetRecordSql(businessType, "");  
                int recordCount = db.ExecuteScalar(sqlCount);     
                int sqlIndex = 0;  
                int rowIndex = 0;  
                foreach (string sqlWhre in sqlWhereArray)                      
                {  
                    sqlIndex++;  
                    FileStream fs = File.Open(fileName, FileMode.Open);    
                    IWorkbook workbook = new XSSFWorkbook(fs);                        
                    ISheet sheet = workbook.GetSheetAt(0);  
                    txtSql.SafeCall(() =>  
                    {  
                        txtSql.AppendText("条件" + sqlIndex.ToString() + "：" + DateRemarkArray[sqlIndex - 1]);  
                    });  
                    string sql = Sql.GetDataSql(businessType, sqlWhre);  
                    DataTable dt = db.GetDataSet(sql).Tables[0];  
      
                    int columnsCount = dt.Columns.Count;  
                    if (sqlIndex == 1)  
                    {  
                        IRow row0 = sheet.CreateRow(0);                              
                        for (int m = 0; m < columnsCount; m++)  
                        {  
                            DataColumn dc = dt.Columns[m];  
                            row0.CreateCell(m).SetCellValue(dc.ColumnName);  
                        }  
                    }  
      
                    for (int i = 0; i < dt.Rows.Count; i++)  
                    {  
                        rowIndex++;  
                        DataRow dr = dt.Rows[i];                          
                        IRow row = sheet.CreateRow(rowIndex);  
                        for (int j = 0; j < columnsCount; j++)  
                        {  
                            row.CreateCell(j).SetCellValue(dr[j].ToString());  
                        }  
      
                        lblMsg.SafeCall(() =>  
                        {  
                            if(i == (dt.Rows.Count - 1))  
                                txtSql.AppendText(" 行数：" + (i+1).ToString() + "rn");  
                            lblMsg.Text = string.Format("正在导出第{0}个条件，第{1}行", sqlIndex.ToString(), (i + 1).ToString());  
                            double x = rowIndex * 1.0 / recordCount * 100;  
                            lblProgress.Text = string.Format("总行数：{0}, 当前完成总{1}行，百分占比：{2} %", recordCount.ToString(), rowIndex.ToString(), x.ToString("#0.0"));  
                        });  
                    }  
                    FileStream outFs = new FileStream(fileName, FileMode.Open);  
                    workbook.Write(outFs);  
                    outFs.Close();  
                }                     
            }).ContinueWith(TaskEnded);  
        }  
        catch (Exception ex)  
        {  
            MessageBox.Show("发生异常，错误提示：" + ex.Message);  
        }  
    }  
    private void TaskEnded(Task task)  
    {  
        txtSql.SafeCall(() =>  
        {  
            lblMsg.Text = "全部导出完成！";  
            txtSql.AppendText("处理完成！rn");                 
        });  
    }  

 Extensions.cs

    public static class Extensions  
    {  
        public static void SafeCall(this Control ctrl, Action callback)  
        {  
            if (ctrl.InvokeRequired)  
                ctrl.Invoke(callback);  
            else  
                callback();  
        }  
        public static void BindComboBox(this ComboBox cb, List<DictionaryEntry> list)  
        {  
            cb.DisplayMember = "Value";  
            cb.ValueMember = "Key";  
            cb.DataSource = list;  
        }  
    }  

 Sql.cs

    using System;  
    using System.Collections.Generic;  
    using System.Linq;  
    using System.Text;  
      
    namespace DataExport  
    {  
        public enum BusinessType  
        {  
            XA = 1,  
            XB = 2  
        }  
      
        public class Sql  
        {  
            /// <summary>  
            /// 分批获取sql的where条件  
            /// </summary>  
            public static string[] SqlWhereArray = {   
                                     " 条件1 ",  
                                     " 条件2 ",  
                                     " 条件3 "  
                                     };  
              
            /// <summary>  
            /// sql的where条件说明  
            /// </summary>  
            public static string[] DateRemarkArray = {    
                                "20130101至20130331",  
                                "20130401至20130630",  
                    "20130701后",  
                                 };  
      
            /// <summary>  
            /// 获取sql语句  
            /// </summary>  
            /// <param name="type"></param>  
            /// <param name="columns"></param>  
            /// <param name="sqlWhere"></param>  
            /// <returns></returns>  
            private static string GetSql(BusinessType type, string columns, string sqlWhere)  
            {  
                string sql = "";  
                switch (type)  
                {  
                    case BusinessType.XA:  
                        sql = string.Format(@"SELECT {0}  FROMM tb1 WHERE 1=1 {1} ", columns, sqlWhere);  
                        break;  
                    case BusinessType.XB:  
                        sql = string.Format(@"SELECT {0}  FROMM tb2 WHERE 1=1 {1} ", columns, sqlWhere);  
                        break;  
                }  
      
      
                return sql;  
            }  
      
            /// <summary>  
            /// 获取总记录数  
            /// </summary>  
            /// <param name="type"></param>  
            /// <param name="sqlWhere"></param>  
            /// <returns></returns>  
            public static string GetRecordSql(BusinessType type, string sqlWhere)  
            {  
                string columns = "count(*)";  
                return GetSql(type, columns, sqlWhere);  
            }  
      
            /// <summary>  
            /// 获取数据  
            /// </summary>  
            /// <param name="type"></param>  
            /// <param name="sqlWhere"></param>  
            /// <returns></returns>  
            public static string GetDataSql(BusinessType type, string sqlWhere)  
            {  
                string columns = "";  
                switch (type)  
                {  
                    case BusinessType.XA:  
                                    columns = @"  
                                    col1 列1,  
                    col2 列2,  
                                    col3 列3  
                                     ";  
                        break;  
                    case BusinessType.XB:  
                                    columns = @"  
                                    col1 列1,  
                    col2 列2  
                                     ";  
                        break;  
                     
                        }  
                return GetSql(type, columns, sqlWhere);  
           }  
        }  
    }