protected void btnLogin_Click(object sender, EventArgs e)
        {
            try //这里做检测，是因为如果没有检测，连接错误后会把数据库里的内容显示在出错网页中
            {
                string username = txtUserName.Text.Trim(); //删除空白字符
                string pwd = txtPwd.Text.Trim();
                if (string.IsNullOrEmpty(username) || string.IsNullOrEmpty(pwd))
                {
                    //Response.Write("用户名或者密码不能为空");
                    Response.Write("<script>alert(‘用户名或者密码不能为空‘);</script>");
                }
                else
                {
                    //写Sql语句
                    string sSql = string.Format("select UserID from TestDB.dbo.UserInfor Where UserName=‘{0}‘ and Pwd=‘{1}‘", username, pwd);

                    //数据库连接语句
                    //DataBase：要连接的数据库名称；  Server：服务器名称，‘.‘代表本机服务器，如果服务器在其他地方，这里输入IP地址
                    //Integrated Security: ture代表windows身份验证，登录名和密码就不需要了；false代表SQL Server身份验证
                    //Uid用户名；Password密码
                    //string connStr = "Database=TestDB;Server=.;Integrated Security=false;Uid=sa;Password=123;";

                    //读取配置文件中的数据库连接语句
                    string connStr = ConfigurationManager.ConnectionStrings["TestDB"].ToString();

                    //普通写法，需要自己释放资源
                    {
                        //和数据库建立连接，并打开连接
                        SqlConnection con = new SqlConnection(connStr);
                        con.Open();

                        //执行语句，要传两个参数，一个是SQL语句，一个是数据库连接类
                        SqlCommand cmd = new SqlCommand(sSql, con);

                        //把查询结果赋值给SqlDataReader对象
                        SqlDataReader read = cmd.ExecuteReader();

                        //查看是否有记录
                        if (read.HasRows)
                        {
                            Response.Redirect("UserInforM.aspx");
                        }
                        else
                        {
                            Response.Write("用户名或者密码错误");
                        }

                        //释放资源,并关闭
                        read.Dispose();
                        read.Close();
                        con.Dispose();
                        con.Close();
                    }

                    //用Using可以自动释放资源
                    {
                        using (SqlConnection con = new SqlConnection(connStr)) //自动释放con
                        {
                            con.Open();
                            SqlCommand cmd = new SqlCommand(sSql, con);
                            using (SqlDataReader read = cmd.ExecuteReader())  //自动释放read
                            {
                                if (read.HasRows)
                                {
                                    Response.Write("登录成功");
                                }
                                else
                                {
                                    Response.Write("用户名或者密码错误");
                                }
                            }
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Response.Write("网站正在维修中");
            }
        }

<connectionStrings>
    <add  name="TestDB" connectionString="Database=TestDB;Server=.;Integrated Security=false;Uid=sa;Password=123;" providerName="System.Data.SqlClient"/>
  </connectionStrings>

 public partial class UserInforM : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            try
            {
                string sSql = string.Format("select UserID,UserName,RealName,ClassName,Major from TestDB.dbo.UserInfor");
                string connStr = ConfigurationManager.ConnectionStrings["TestDB"].ToString();

                using (SqlConnection con = new SqlConnection(connStr)) //自动释放con
                {
                    con.Open();
                    SqlCommand cmd = new SqlCommand(sSql, con);
                    using (SqlDataReader read = cmd.ExecuteReader())  //自动释放read
                    {
                        GridView1.DataSource = read;
                        GridView1.DataBind();
                    }
                }
            }
            catch (Exception ex)
            {

                Response.Write("错误");
            }
        }
    }