怎么都连接不上

package enter;import java.sql.*;public class enter
{
public String user_name;
public String user_key;public Connection con;public boolean enter_exe() throws Exception {
  try{Statement statement=con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
String sql="select * from user_info where user_name='"+user_name+"' and user_key='"+user_key+"'";
ResultSet r=statement.executeQuery(sql);if(!r.first())
{return false;}
else
{return true;}}catch(SQLException ee)
{
return false;
}}
<%@ page contentType="text/html; charset=GBK" %><jsp:useBean id="j" scope="application" class="jdbc.jdbc"/>
<jsp:useBean id="e" scope="application" class="enter.enter"/>
<jsp:useBean id="m" scope="application" class="MD5.MD5"/><script Language=javascript>
<!--
function returnback()
{TimerID=setTimeout('window.location.href="index.htm"',1000)
}
-->
</script><body onload="returnback()"><%
e.con=j.getConnection();String user_name=new String(request.getParameter("user_name").getBytes("ISO8859_1"), "GBK");
String user_key=new String(request.getParameter("user_key").getBytes("ISO8859_1"), "GBK");
user_key=m.getMD5ofStr(user_key);
e.user_name=user_name;
e.user_key=user_key;
if(e.enter_exe())
{
out.print("登陆成功！");
request.getSession(true);
session.putValue("enter","wushili");
session.putValue("user_name",user_name);
}
else
{
out.print("用户名或密码错误！");
}
j.releaseConnection(e.con);
%>