Spring 重构常见的控制器重定向代码

Question

我的控制器类中有一些重定向代码，我想重构。这些代码只是检查对象是否为空，如果是...它会将其重定向到特定页面。

以下是代码的一部分：

@RequestMapping(value = "/user-details", method = RequestMethod.GET)
public ModelAndView userDetails(@RequestParam("id") int id) {
    ...
    User user = userService.getUserById(id);
    if (matter == null) {
        return new ModelAndView("redirect:/users-list.html");
    }
    ...
}
@RequestMapping(value = "/user-application-details", method = RequestMethod.GET)
public ModelAndView userApplicationDetails(@RequestParam("applicationId") int applicationId) {
    ...
    UserApplication application = userApplicationService.getApplicationById(applicationId);
    if (application == null) {
        return new ModelAndView("redirect:/users-list.html");
    }
    ...
}
@RequestMapping(value = "/user-activity-details", method = RequestMethod.GET)
public ModelAndView userActivityDetails(@RequestParam("activityId") int activityId) {
    ...
    UserActivity activity = userActivityService.getActivityById(activityId);
    if (activity == null) {
        return new ModelAndView("redirect:/users-list.html");
    }
    ...
}

我想重构空检查并重定向到一个单独的类，但我不确定如何在控制器中调用它并将重定向到指定页面。

Answer 1

检查控制器中是否存在变量是可以的。您可以使用 Java 8 Optional API 改进语法。

您可以做的是将异常处理移动到单独的类中。 Spring 有一个特殊的组件注释，正是针对这个用例的：@ControllerAdvice附带@ExceptionHandler方法。这确实需要您引发异常。

有关示例，请参阅：

@Controller
public class SampleController {
    @RequestMapping(value = "/user-details", method = RequestMethod.GET)
    public ModelAndView userDetails(@RequestParam("id") int id) {
        ...
        Optional<User> userOptional = userService.getUserById(id);
        User user = userOptional.orElseThrow(() -> new UserNotFoundException("message here"));
        ...
    }
}
@ControllerAdvice
public class SampleControllerAdvice {
    private static final String REDIRECT_USER_LIST = "redirect:/users-list.html";
    @ExceptionHandler
    public String handleUserNotFound(UserNotFoundException e, RedirectAttributes redirectAttributes) {
        redirectAttributes.addFlashAttribute("errorMessage", e.getMessage());
        return REDIRECT_USER_LIST;
    }
    @ExceptionHandler
    public String handleUserActivityNotFound(UserActivityNotFoundException e, RedirectAttributes redirectAttributes) {
        redirectAttributes.addFlashAttribute("errorMessage", e.getMessage());
        return REDIRECT_USER_LIST;
    }
}