// Web.Config
<?xml version="1.0" encoding="utf-8"?>
<!--
  有关如何配置 ASP.NET 应用程序的详细信息，请访问
  http://go.microsoft.com/fwlink/?LinkId=169433
  -->

<configuration>

    <system.web>
      <compilation debug="false" targetFramework="4.5" />
      <httpRuntime targetFramework="4.5" />
    </system.web>
  <appSettings>
    <add key="connectionString" value="server=.;database=stuTest;    uid=sa;pwd=123456"/>
  </appSettings>
</configuration>


// 获取配置文件信息
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

public partial class GridViewPage_One : System.Web.UI.Page
{
    //第一种写法已经过时，会提示错误信息将ConfigurationSettings改成ConfigurationManager
　　 //然后在命名空间中加入using System.Configuration;
    // private string connectionString = ConfigurationSettings.AppSettings["connectionString"].ToString();
    private string connectionString = ConfigurationManager.AppSettings["connectionString"].ToString();

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            FillList();
        }
    }
    private void FillList()
    {
        string selectSql = "select * from Stu";
        SqlConnection con = new SqlConnection(connectionString);
        SqlCommand cmd = new SqlCommand(selectSql,con);
        SqlDataAdapter adapter = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();

        try
        {
            con.Open();
            adapter.Fill(ds,"Students");
            this.GridView1.DataSource = ds.Tables["Students"].DefaultView;
            this.GridView1.DataBind();
        }
        catch(Exception err)
        {
            throw err;
        }
    }
}