使用using{}，去掉数据库连接的.Close()方法，using自动会调用Dispose()来关闭数据库连接

using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;using System.Data.SqlClient;public partial class ConnectSQL_PageOne : System.Web.UI.Page{    protected void Page_Load(object sender, EventArgs e)    {        string conText = System.Web.Configuration.WebConfigurationManager.ConnectionStrings["zlconn"].ToString();        SqlConnection conn = new SqlConnection();        conn.ConnectionString = conText;        using (conn)        {            conn.Open();            //不必再写conn.Close();在using中，会自动调用conn.Close();            Response.Write(conn.State.ToString());            Response.Write("<br/>");        }        Response.Write(conn.State.ToString());    }}