关于JSP连接池出错请教大家！

我的JSP采用连接池，在调用连接池时候出现错误，如下错误：

javax.servlet.ServletException: javax.naming.NameNotFoundException: Name jdbc is not bound in this Context



下面是我的连接接代码：

import java.sql.*;
import javax.naming.*;
import javax.sql.DatabaseSource;

public class DBConn{

       public static sychronized Connection getConnection()throws Exception{

                  

                  try{
                  Connection cn=new InitialConnection();
                  Connection dn=(Connection)cn.lookup("java:comp/env");
                  DatabaseSource ds=(DatabaseSource)dn.lookup("jdbc/db_shop");
                  return ds.getConnection();
                      }


                  catch(NamingException e){
                     throws e;
                                          }
                  catch(SQLException e){
                     throws e;
                                       }

                                                             }

                   }

上面的错误是我在应用在我的JSP网站的时候页面给我提示的错误！！请大家帮我看看，谢谢了！！