jsp求救

package dorm;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import dorm.*;
import java.sql.*;

public class Land extends HttpServlet
{

//Initialize global variables
  public void init() throws ServletException
  {
  }
   
  //Process the HTTP Post request
public void service(HttpServletRequest req,HttpServletResponse res)
throws ServletException,IOException
{
req.setCharacterEncoding("gb2312");
res.setContentType("text/html;charset=gb2312");
PrintWriter pw=res.getWriter();
String username=req.getParameter("username");
String password=req.getParameter("password");

   
Connection conn=null;
  Statement state=null;
  ResultSet rs=null;
  String url="jdbc:microsoft:sqlserver://127.0.0.1:1433;DatabaseName=dorm";
String drivername="com.microsoft.jdbc.sqlserver.SQLServerDriver";
String sql="select * from users where username='"+username+"' and password='"+password+"';";



if(username.equals("")||password.equals(""))
  pw.print("<script>alert('请输入帐号和密码!');history.back()</script>");