Spring Security 身份验证处理抛异常 重复执行？

Spring Security loadUserByUsername（String username）方法抛出异常后重新执行了，且username为空

有点不解，为什么会多次执行

具体的代码如下

自定义的登录接口 Controller如下

@RestController
public class UserLoginController {
    @Autowired
    UserLoginService userLoginService;

    @RequestMapping(method = RequestMethod.POST, value = "/doLogin")
    public ResponseEntity userLogin(@Validated @RequestBody User user) {

        Result result = userLoginService.userLogin(user);

        return ResponseEntity.ok(result);
    }
}

实现类业务逻辑如下：

    @Autowired

    AuthenticationManager authenticationManager;

    @Autowired
    RedisUtil redisUtil;

    @Override
    public Result userLogin(User user) {

        UsernamePasswordAuthenticationToken authenticationToken = new UsernamePasswordAuthenticationToken
                (user.getUsername(), user.getPassword());
        Authentication authenticate = authenticationManager.authenticate(authenticationToken);
        if (ObjectUtils.isEmpty(authenticate)) {
            throw new RuntimeException("账号密码错误，请检查账号密码");
        }
        LoginUser user1 = (LoginUser) authenticate.getPrincipal();
        String uid = user1.getUser().getUid().toString();
        String token = JwtUtil.createJWT(uid);
        redisUtil.set("login:" + uid, user1);
        Map map = new HashMap();
        map.put("token", token);
        return ResultResponse.getSuccessandMessage(map, "登录成功");
    }
}

UserDetailService具体逻辑代码如下 这里加了个变量num来打印执行的次数

  private static int num = 0;

    @Override
    public UserDetails loadUserByUsername(String username) {
        System.out.println(++num);
        User user;
        String regex = "^\\w+([-+.]\\w+)*@\\w+([-.]\\w+)*\\.\\w+([-.]\\w+)*$";
        //邮箱登录逻辑
        if (username.matches(regex)) {
            Email email = emailService.getByEmail(username);
            if (ObjectUtils.isEmpty(email)) {
                System.out.println("邮箱不存在抛出异常——");
                throw new ValidateCodeException("邮箱不存在");
            } else {
                if (email.getCheck() != 1) {
                    throw new ValidateCodeException("邮箱未启用");
                }
                user = userService.findByUId(email.getUid());
            }
        } else {
            user = userService.getUserByname(username);
        }
        if (ObjectUtils.isEmpty(user)) {
            System.out.println("账号不存在 抛出异常");
            throw new RuntimeException("用户不存在");
        }
        return new LoginUser(user);
    }

具体配置如下

@Override
    protected void configure(HttpSecurity http) throws Exception {
        //关闭csrf防护
        http.csrf().disable();
        //开启表单验证
        http.formLogin().failureHandler(myAuthenticationFailedHandler).and()
                .authorizeRequests().antMatchers("/doLogin").permitAll().
                anyRequest().authenticated();
    }

当用户不存在时抛出异常时，发现重复调用loadUserByUsername方法