JDBC连接数据库简单有关问题，菜鸟

package jdbc;import java.io.IOException;import java.sql.*;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class JDBCTest extends HttpServlet {        public void process(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException{        Connection conn=null;//连接对象        PreparedStatement pstmt=null;//预编译的语句对象        ResultSet rs=null;//查询结果集        String sql=null;        try{            Class.forName("com.mysql.jdbc.Driver");//加载驱动            //建立连接            conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbctest","root","root");            //创建语句对象            sql="select*from myuser where user_id=?and user_pass=?";            pstmt=conn.prepareStatement(sql);            pstmt.setString(1, "zhangsan");            pstmt.setString(2, "123");            rs=pstmt.executeQuery();//执行SQL语句            //处理结果            while(rs!=null&&rs.next()){                System.out.println("user_no"+rs.getString(1));                System.out.println("user_id="+rs.getString(2));                System.out.println("user_email="+rs.getString(5));            }        }catch(Exception e){            System.out.println("数据库异常");            e.printStackTrace();        }finally{//按打开对象的逆序关闭对象            try{                if(rs!=null)                    rs.close();                if(pstmt!=null)                    pstmt.close();                if(conn!=null)                    conn.close();            }catch(Exception e){                            }        }    }    public JDBCTest() {        super();    }     public void destroy() {        super.destroy(); // Just puts "destroy" string in log            }    public void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        process(request,response);    }    public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        process(request,response);    }    public void init() throws ServletException {            }}