package com.PIM.dao;public class UserDao {????public boolean exsit(String name) throws SQLException { Connection conn=DBUtil.getConnection(); String sql="" + " select * from imooc_goddess " + " where user_name=? "; PreparedStatement ptmt=conn.prepareStatement(sql); ptmt.setString(1, name); ResultSet rs=ptmt.executeQuery(); if(rs!=null){ return true; } else{ return false; }}jsp 頁面：<%@ page language="java" import="java.util.* ,com.PIM.dao.*,com.PIM.model.*" contentType ="text/html; charset=utf-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; String password = null;?request.setCharacterEncoding("utf-8"); //只是針對POST方式提交的請求，對GET方式無效。?response.setContentType("text/html;charset=utf-8");?UserDao ud= new UserDao();//報(bào)錯的地方~~~~~~~~~~~~~~~?。。。。。。?！~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~?boolean a = ud.exsit("565203087");//寫死，數(shù)據(jù)庫中有這條數(shù)據(jù)。但是調(diào)用總是報(bào)錯。 if(a){ request.getRequestDispatcher("main.jsp").forward(request,response);//服務(wù)器內(nèi)部轉(zhuǎn)發(fā) } else{ response.sendRedirect("Registion.jsp");//請求重定向 }%>main 方法：UserDao ud = new UserDao();boolean a = ud.exsit("565203087"); System.out.println(a);//一切正常，服務(wù)臺能返回true????