实例化Servlet类[com.atguigu.web.RegistServlet]异常

Question

web实现类里面  实例化一个UserService类用来进行数据库存储  

UserService 已经进行了Test ，没有问题  ，但在这里总是报错“ 实例化Servlet类[com.atguigu.web.RegistServlet]异常”

求救

代码如下：
实现类RegistServlet

package com.atguigu.web;

import com.alibaba.druid.support.json.JSONUtils;
import com.atguigu.pojo.User;
import com.atguigu.service.UserService;
import com.atguigu.service.impl.UserServiceImpl;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class RegistServlet extends HttpServlet {


    UserServiceImpl userService = new UserServiceImpl();

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //  1、获取请求的参数
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String email = req.getParameter("email");
        String code = req.getParameter("code");

//        2、检查 验证码是否正确  === 写死,要求验证码为:abcde
        if ("abcde".equalsIgnoreCase(code)) {
//        3、检查 用户名是否可用
            if (userService.existUsername(username)) {
                System.out.println("用户名[" + username + "]已存在!");
//        跳回注册页面
                req.getRequestDispatcher("/pages/user/regist.html").forward(req, resp);
            } else {
                //      可用
//                调用Sservice保存到数据库
                userService.registUser(new User(null, username, password, email));
//
//        跳到注册成功页面 regist_success.html
                req.getRequestDispatcher("/pages/user/regist_success.html").forward(req, resp);
            }
        } else {
            System.out.println("验证码[" + code + "]错误");
            req.getRequestDispatcher("/pages/user/regist.html").forward(req, resp);
        }
    }
}

UserService接口

package com.atguigu.service;

import com.atguigu.pojo.User;

public interface UserService {


    public void registUser(User user);

    public User login(User user);

    public  boolean existUsername(String username);

}

UserServiceImpl实现

package com.atguigu.service.impl;

import com.atguigu.dao.UserDao;
import com.atguigu.dao.impl.UserDaoImpl;
import com.atguigu.pojo.User;
import com.atguigu.service.UserService;

public class UserServiceImpl implements UserService {

    private UserDao userDao = new UserDaoImpl();

    @Override
    public void registUser(User user) {
        userDao.saveUser(user);
    }

    @Override
    public User login(User user) {
        return userDao.queryUserByUsernameAndPassword(user.getUsername(),user.getPassword());
    }

    @Override
    public boolean existUsername(String username) {
        if(userDao.queryUserByUsername(username)==null){
            return false;
        }
        return true;
    }
}

Answer 1

UserServiceImpl userService = new UserServiceImpl();

改为

@Autowired

UserServiceImpl userService;

试试