C#中使用NPOI导入导出CSV文件

1.首先（NPOI官网下载dll）

添加引用：NPOI.dll，NPOI.OOXML.dll，NPOI.OpenXml4Net.dll，NPOI.OpenXmlFormats.dll

2.代码——CSVHelper

  1     public class CSVHelper
  2     {
  3         /// <summary>
  4         /// 写入CSV
  5         /// </summary>
  6         /// <param name="fileName">文件名</param>
  7         /// <param name="dt">要写入的datatable</param>
  8         public static void WriteCSV(string fileName,DataTable dt)
  9         {
 10             FileStream fs;
 11             StreamWriter sw;
 12             string data = null;
 13 
 14             //判断文件是否存在,存在就不再次写入列名
 15             if (!File.Exists(fileName))
 16             {
 17                  fs = new FileStream(fileName, FileMode.Create, FileAccess.Write);
 18                  sw = new StreamWriter(fs, Encoding.UTF8); 
 19 
 20                 //写出列名称
 21                 for (int i = 0; i < dt.Columns.Count; i++)
 22                 {
 23                      data += dt.Columns[i].ColumnName.ToString();
 24                     if (i < dt.Columns.Count - 1)
 25                     {
 26                         data += ",";//中间用，隔开
 27                     }
 28                 }
 29                 sw.WriteLine(data);
 30             }
 31             else
 32             {
 33                  fs = new FileStream(fileName, FileMode.Append, FileAccess.Write);
 34                  sw = new StreamWriter(fs, Encoding.UTF8); 
 35             }
 36             
 37             //写出各行数据
 38             for (int i = 0; i < dt.Rows.Count; i++)
 39             {
 40                 data = null;
 41                 for (int j = 0; j < dt.Columns.Count; j++)
 42                 {
 43                     data += dt.Rows[i][j].ToString();
 44                     if (j < dt.Columns.Count - 1)
 45                     {
 46                         data += ",";//中间用，隔开
 47                     }
 48                 }
 49                 sw.WriteLine(data);
 50             } 
 51             sw.Close();
 52             fs.Close(); 
 53         }
 54 
 55 
 56 
 57         /// <summary>
 58         /// 读取CSV文件
 59         /// </summary>
 60         /// <param name="fileName">文件路径</param>
 61         public static DataTable ReadCSV(string fileName)
 62         {
 63             DataTable dt = new DataTable();
 64             FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
 65             StreamReader sr = new StreamReader(fs, Encoding.UTF8);
 66 
 67             //记录每次读取的一行记录
 68             string strLine = null;
 69             //记录每行记录中的各字段内容
 70             string[] arrayLine=null;
 71             //分隔符
 72             string[] separators = { "," };
 73             //判断，若是第一次，建立表头
 74             bool isFirst = true;
 75 
 76             //逐行读取CSV文件
 77             while ((strLine = sr.ReadLine()) != null)
 78             {
 79                 strLine = strLine.Trim();//去除头尾空格
 80                 arrayLine = strLine.Split(separators, StringSplitOptions.RemoveEmptyEntries);//分隔字符串，返回数组
 81                 int dtColumns = arrayLine.Length;//列的个数
 82 
 83                 if (isFirst)  //建立表头
 84                 {
 85                     for (int i = 0; i < dtColumns; i++)
 86                     {
 87                         dt.Columns.Add(arrayLine[i]);//每一列名称
 88                     }
 89                 }
 90                 else   //表内容
 91                 {
 92                     DataRow dataRow = dt.NewRow();//新建一行
 93                     for (int j = 0; j < dtColumns; j++)
 94                     {
 95                         dataRow[j] = arrayLine[j];
 96                     }
 97                     dt.Rows.Add(dataRow);//添加一行
 98                 }
 99             }
100             sr.Close();
101             fs.Close();
102 
103             return dt;
104         }