将数据库中的数据导出到Excel

private void button1_Click(object sender, EventArgs e)
{
string sql = "select * from Employee";
using(SqlDataReader reader = DBHelper.ExecuteDataReader (sql,CommandType.Text))
{
if (reader.HasRows)
{
//如果有读到数据 则创建一个Excel工作薄Workbook
IWorkbook wk = new HSSFWorkbook();

//创建一个工作表Sheet
ISheet employeeSheet = wk.CreateSheet("EmployeeMsg");

int rowIndex = 0;    //用来维护行的索引

while (reader.Read())
{
#region  循环一次就从数据库中获取一行数据
int id = reader.GetInt32(0);
string name = reader.IsDBNull(1) ? null : reader.GetString(1);
string gender = reader.IsDBNull(2) ? null : reader.GetString(2);
int? age = reader.IsDBNull(3) ? null : (int?)reader.GetInt32(3);
decimal? salary = reader.IsDBNull(4) ? null : (decimal?)reader.GetDecimal(4);
string tel = reader.IsDBNull(5) ? null : reader.GetString(5);
#endregion

// 每循环一次 为Sheet中添加一行
IRow row = employeeSheet.CreateRow(rowIndex);

// 为行添加单元格
row.CreateCell(0).SetCellValue(id);
row.CreateCell(1).SetCellValue(name);
row.CreateCell(2).SetCellValue(gender);
//  报错  row.CreateCell(3).SetCellValue(age);   得做空值处理
if (age == null)
{
row.CreateCell(3, CellType.BLANK);    // 如果值为null  则创建一个空单元格
}
else
{
row.CreateCell(3).SetCellValue((int)age);
}
// row.CreateCell(4).SetCellValue(salary);
if (salary == null)
{
row.CreateCell(4, CellType.BLANK);
}
else
{
row.CreateCell(4, CellType.NUMERIC).SetCellValue((double)salary);
}
if (tel == null)
{
row.CreateCell(5, CellType.BLANK);
}
else
{
row.CreateCell(5).SetCellValue(tel);
}

rowIndex++;
}
// 创建文件流  想Excel中写入数据
using (FileStream fs = File.OpenWrite("employee.xls"))
{
wk.Write(fs);
MessageBox.Show("写入成功");
}
}
else
{
MessageBox.Show("表中无数据");
}
}
}