GridView

using System.Data;

using System.Data.OleDb;

protected void Page_Load(object sender, EventArgs e)

{

    string connString = string.Format("Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0};Extended Properties=Text;", Server.MapPath("~"));

    string cmdString = string.Format("SELECT * FROM {0}", "Customers.csv");

    OleDbDataAdapter dataAdapter = new OleDbDataAdapter(cmdString, connString);

    DataSet dataSet = new DataSet();

    dataAdapter.Fill(dataSet);

    GridView1.DataSource = dataSet;

    GridView1.DataBind();

}

using System.Data;

using System.Data.OleDb;

protected void Page_Load(object sender, EventArgs e)

{

    string connectionString = String.Format(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties=""Excel 8.0;HDR=YES;IMEX=1;""", Server.MapPath("Customers.xlsx"));

    string query = String.Format("select * from [{0}$]", "Sheet1");

    OleDbDataAdapter dataAdapter = new OleDbDataAdapter(query, connectionString);

    DataSet dataSet = new DataSet();

    dataAdapter.Fill(dataSet);

    GridView1.DataSource = dataSet.Tables[0];

    GridView1.DataBind();

}