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我们在login.html页面输入用户名和密码点击登录，请求访问到/login，然后在login方法里获取User对象，在到UserService的login方法中判断登录，来依照这个逻辑，来完成剩下的功能：

<div style="color:red;" th:text="${loginError}" th:if="${not #strings.isEmpty(loginError)}"></div><br>
<form th:action="@{/login}" method="post">用户名：<input type="text" name="username" placeholder="请输入用户名"/><br/><br/>密　码：<input type="password" name="pasword" placeholder="请输入密码"/><br/><br/><input style="margin-left:60px;" type="submit" value="登录"/>
</form>

1、在数据库中加一条记录

 2、完成UserDao接口

public interface UserDao extends JpaRepository<User, Integer> {
}

3、完成UserService接口和UserServiceImpl实现类

public interface UserService{public void add(User user);public void delete(int id);public void update(User user);public User getOneById(int id);public List<User> getAll();public Page<User> getAll(Pageable pageable);
}
@Service("userService")
public class UserServiceImpl implements UserService {@Autowiredprivate UserDao userDao;@Overridepublic void add(User user) {userDao.save(user);}@Overridepublic void delete(int id) {userDao.deleteById(id);}@Overridepublic void update(User user) {userDao.saveAndFlush(user);}@Overridepublic User getOneById(int id) {return userDao.findById(id).get();}@Overridepublic List<User> getAll() {return userDao.findAll();}@Overridepublic Page<User> getAll(Pageable pageable) {return userDao.findAll(pageable);}
}

4、完成登录的逻辑

@PostMapping("/login")
public String login(User user) {boolean flag = false;flag = userService.login(user);if (flag) {  //放置重复提交，登录成功后，做过重定向return "redirect:/main.html";} else {return "redirect:/index.html";}
}
@Override
public boolean login(User user) {User u = null;if(!StringUtils.isEmpty(user.getUsername())){u = userDao.getUserByUsername(user.getUsername());}if(u==null) return false;if(user.getPasword().equals(u.getPasword())){return true;}else {return false;}
}