1.修改UserService.java

package com.imooc.oa.service;

import com.imooc.oa.entity.User;
import com.imooc.oa.mapper.UserMapper;
import com.imooc.oa.service.exception.LoginException;
import com.imooc.oa.utils.Md5Utils;

public class UserService {
    private UserMapper userMapper = new UserMapper();
    /**
     * 根据前台输入进行登录校验
     * @param username 前台输入的用户名
     * @param password 前台输入的密码
     * @return 校验通过后,包含对应用户数据的User实体类
     * @throws LoginException 用户登录异常
     */
    public User checkLogin(String username , String password){
        User user = userMapper.selectByUsername(username);
        if(user == null){
            throw new LoginException("用户名不存在");
        }
        String md5 = Md5Utils.md5Digest(password, user.getSalt());
        if(!md5.equals(user.getPassword())){
            throw new LoginException("密码错误");
        }
        return user;
    }
}

2.LoginServlet.java的处理

如果不处理返回的使用户的全部信息，对用户的密码和盐值进行处理
 user.setPassword(null);
 user.setSalt(null);

package com.imooc.oa.controller;

import com.imooc.oa.entity.User;
import com.imooc.oa.service.UserService;
import com.imooc.oa.utils.ResponseUtils;

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

@WebServlet("/api/login")
public class LoginServlet extends HttpServlet {
    private UserService userService = new UserService();
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        response.setContentType("application/json;charset=utf-8");
        //接收用户输入
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        //调用业务逻辑
        ResponseUtils resp = null;
        try {
            User user = userService.checkLogin(username, password);
            user.setPassword(null);
            user.setSalt(null);
            //处理结果编码,0代表处理成功,非0代表处理失败
            resp = new ResponseUtils().put("user", user);
        }catch (Exception e){
            e.printStackTrace();
            resp = new ResponseUtils(e.getClass().getSimpleName(), e.getMessage());
        }
        //返回JSON结果
        response.getWriter().println(resp.toJsonString());
    }
}