spring mvc应用程序中向数据库添加重复用户名异常处理

// 自定义异常类
public class DuplicateUsernameException extends RuntimeException {
    // 自定义异常信息
    public DuplicateUsernameException(String message) {
        super(message);
    }
}

// 业务逻辑层
@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    public void addUser(User user) {
        // 判断用户名是否已存在
        if (userRepository.findByUsername(user.getUsername()) != null) {
            throw new DuplicateUsernameException("Username already exists.");
        }
        // 添加用户到数据库
        userRepository.save(user);
    }
}

// 控制器层
@Controller
public class UserController {
    @Autowired
    private UserService userService;

    @PostMapping("/users")
    public String addUser(@ModelAttribute User user) {
        try {
            userService.addUser(user);
            return "success";
        } catch (DuplicateUsernameException e) {
            // 处理重复用户名异常
            return "error";
        }
    }
}

// 异常处理器
@ControllerAdvice
public class GlobalExceptionHandler implements HandlerExceptionResolver {
    @Override
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        if (ex instanceof DuplicateUsernameException) {
            // 处理重复用户名异常
            return new ModelAndView("error");
        }
        // 其他异常处理逻辑
        return new ModelAndView("error");
    }
}