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 {
            }

}