求教，servlet登录数据库没有东西输出

import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.sql.*;public class login extends HttpServlet {
private Connection conn=null;
private ResultSet rst=null;
//private PreparedStatement pstm=null;
private Statement stm=null;

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String name=new String(request.getParameter("name").getBytes("UTF-8"),"gbk");
String pwd=new String(request.getParameter("pwd").getBytes("UTF-8"),"gbk");
response.setContentType("text/html;charset=gbk");
PrintWriter out = response.getWriter();
String sql="select * from user where u_name='"+name+"'and u_password='"+pwd+"'";

try{

stm=conn.createStatement();

rst=stm.executeQuery(sql);//问题出现在这

while(rst.next()){
out.write("登录成功");

//response.sendRedirect("login.jsp"); 
}
}catch(Exception e)
{
e.getStackTrace();
}
out.flush();
out.close(); } public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
} /**
 * Initialization of the servlet. <br>
 *
 * @throws ServletException if an error occurs
 */
public void init(ServletConfig config) throws ServletException {
super.init(config);
 try{
 
        Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");//加载驱动程序
         }
      catch(ClassNotFoundException e)
         { 
       System.out.println("找不到驱动");
         }
      try{
            conn=DriverManager.getConnection("jdbc:odbc:ping","ggping","660309");
           
         }
      catch(SQLException e)  
         {
       e.printStackTrace();
         }

}
public void destroy() {
super.destroy(); 
try{ if(rst!=null) rst.close();
 //if(pstm!=null)pstm.close();
 if(conn!=null)conn.close();
 if(stm!=null)stm.close();
  }catch(Exception e)
  {
  e.getStackTrace();
  }
}
}