写：

StreamWriter sw ;
sw = File.CreateText(@"e:\aa.txt");
sw.WriteLine(TextBox2.Text);
sw.Close();

读：

if (FileUpload1.PostedFile.FileName != "")
        {
            FilePath = FileUpload1.PostedFile.FileName;
            fileExtName = FilePath.Substring(FilePath.LastIndexOf(".") + 1, 3);
            if (fileExtName.Equals("txt"))
            {
                StreamReader fileStream = new StreamReader(this.FileUpload1.PostedFile.InputStream, Encoding.Default);

                string filestr = fileStream.ReadToEnd();
                fileStream.Close();
                TextBox2.Text = filestr;
            }
            else
            {
                Response.Write("错了");
            }
        }

读Execl

string strFileName = FileUpload1.FileName;
        string imgpath = Server.MapPath("~/inputFile/");
        FileUpload1.SaveAs(imgpath + strFileName);
        try
        {
            string strConn = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=" + imgpath + "\\" + strFileName + ";" + "Extended Properties=Excel 8.0;";
            OleDbConnection conn = new OleDbConnection(strConn);
            OleDbDataAdapter oda = new OleDbDataAdapter("select * from [Sheet1$]", strConn); //oda.Fill(ds);
            oda.Fill(ds,"aa");
            GridView1.DataSource = ds.Tables["aa"];
            GridView1.DataBind();

        }
        catch (Exception ex)
        {
            Response.Write(ex.ToString());
        }