java - 处理索引 0 超出长度 0 的范围以验证用户方法

Question

我有这种方法可以验证用户尝试登录我在 Tomcat 上托管的 Web 应用程序，如果我输入不存在的用户名，它会给我一个 Index 0 out of bounds for length 0而不是返回 null 并显示无效的登录凭据页面。如果用户名不存在，如何确保它返回 null？

验证用户方法:

 public User validateUser(Login login) {

// SQL statement
String sql = "select * from users where username='" + login.getUsername() + "'";
// Running query
List<User> users = jdbcTemplate.query(sql, new UserMapper());
User user = users.get(0);
// Getting encrypted password
String encodedPassword = user.getPassword();
// Getting login password
String rawPassword = login.getPassword();
// Validating them
boolean isPasswordMatch = passwordEncoder.matches(rawPassword, encodedPassword);
if(isPasswordMatch){
    return user;
}
else { 
    return null;
}
}

Controller :

@RequestMapping(value = "/loginProcess", method = RequestMethod.POST)
public ModelAndView loginProcess(HttpServletRequest request, HttpServletResponse response,
@ModelAttribute("login") Login login) {
ModelAndView mav = null;
// Validating user
User user = userService.validateUser(login);
if (null != user) {
// Setting view
mav = new ModelAndView("loginProcess", "firstname", user.getFirstname());
// Creating session and saving user
HttpSession httpSession = request.getSession(true);
httpSession.setAttribute("User", user);
}
// Returning invalid credentials
return mav = new ModelAndView("loginIncorrect");
}

Answer 1

如果用户的长度为零，则可以返回 null