因此，我尝试使用POST登录名API对用户进行身份验证，但问题是当用户不存在时(意味着用户名(唯一)不在数据库中)，抛出的错误消息不会显示在客户端(POSTMAN)。我尝试调试，但抛出错误，但没有显示。我看到的只是POSTMAN中的Status: 401 Unauthorized
但是，当用户存在但密码不匹配时，它会显示正确的抛出错误消息。注意：我使用的是Spring的OAuth 2.0资源服务器JWT
控制器法

@PostMapping(path = "/login", consumes = "application/json")
    public ResponseEntity<?> login(@Valid @RequestBody UserDTO userDTO) throws UsernameNotFoundException {
        LOGGER.info("Authenticating {}", userDTO.getUsername());

        userDTOService.confirmUser(userDTO); // Where the issue occurs

        Authentication authentication = authenticationManager
                .authenticate(new UsernamePasswordAuthenticationToken(userDTO.getUsername(), userDTO.getPassword()));

        return ResponseEntity.ok()
                .header(
                        HttpHeaders.AUTHORIZATION,
                        tokenService.generateToken(authentication)
                )
                .build();
    }

服务方式(确认用户方式)

public void confirmUser(UserDTO userDTO) throws UsernameNotFoundException {
        /*
        * Check if username exist in the database
        * Check if the password provided equals password in database
        * */
        String username = userDTO.getUsername();
        String password = userDTO.getPassword();
        Optional<User> user = userRepository.findUserByUserName(username);

        // This error is not displayed
        if (user.isEmpty()) {
            LOGGER.error("User {} does not exist", username);
            throw new UsernameNotFoundException(username + " does not exist");
        }

        boolean checkingCredentials = user
                .stream()
                .anyMatch(
                        param ->
                                param.getUsername().equals(username)
                                        &&
                                        passwordEncoder.matches(password, param.getPassword())
                );

        if (!checkingCredentials) {
            LOGGER.error("Bad user credentials");
            throw new RuntimeException("Please check username or password");
        }

    }