在spring安全登录中添加额外的用户需求，并处理各种异常

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
</dependency>

@Service
public class CustomUserDetailsService implements UserDetailsService {

    @Autowired
    private UserRepository userRepository;

    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        User user = userRepository.findByUsername(username);
        if (user == null) {
            throw new UsernameNotFoundException("User not found");
        }
        return new org.springframework.security.core.userdetails.User(user.getUsername(), user.getPassword(), new ArrayList<>());
    }
}

@Entity
@Table(name = "users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(unique = true)
    private String username;

    private String password;

    // Getters and setters
}

<form th:action="@{/login}" method="post">
    <div>
        <label for="username">Username:</label>
        <input type="text" id="username" name="username" required autofocus/>
    </div>
    <div>
        <label for="password">Password:</label>
        <input type="password" id="password" name="password" required/>
    </div>
    <div>
        <button type="submit">Login</button>
    </div>
</form>

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Autowired
    private CustomUserDetailsService userDetailsService;

    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth.userDetailsService(userDetailsService);
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/login").permitAll()
                .anyRequest().authenticated()
                .and()
            .formLogin()
                .loginPage("/login")
                .defaultSuccessUrl("/home")
                .permitAll()
                .and()
            .logout()
                .permitAll();
    }
}

@ControllerAdvice
public class CustomExceptionHandler {

    @ExceptionHandler(UsernameNotFoundException.class)
    public ResponseEntity<String> handleUsernameNotFoundException(UsernameNotFoundException ex) {
        return ResponseEntity.status(HttpStatus.UNAUTHORIZED).body(ex.getMessage());
    }

    @ExceptionHandler(AuthenticationException.class)
    public ResponseEntity<String> handleAuthenticationException(AuthenticationException ex) {
        return ResponseEntity.status(HttpStatus.UNAUTHORIZED).body(ex.getMessage());
    }
}