如何在签名中没有 RedirectAttributes 的方法中访问 RedirectAttributes？

Question

In a Spring Boot controller, is it possible to access RedirectAttributes in a method without RedirectAttributes in its signature? In other words, can it be accessed from the framework as a "bean" or context variable?

My motivation for doing this is to be able to refactor several request mapping methods (à la Clean Code ) to move exception handling out of those methods. So, for example, I have several methods with a catch block like this:

    @GetMapping("/security/user/{uid}")
    public String showEditUserForm(@PathVariable("uid") String uid, Model model, RedirectAttributes redirectAttributes) {
        try {
            model.addAttribute("userAccount", userAccountService.findByUsername(uid));
            return "/security/edituser";
        } catch(UserDoesntExistException e) {
            redirectAttributes.addFlashAttribute("flashstatus","danger");
            redirectAttributes.addFlashAttribute("flashmessage","User doesn't exist");
            return "redirect:/security";
        }
    }

Instead, I'd like to do something like this:

    @GetMapping("/security/user/{uid}")
    public String showEditUserForm(@PathVariable("uid") String uid, Model model) {
        try {
            model.addAttribute("userAccount", userAccountService.findByUsername(uid));
            return "/security/edituser";
        } catch(UserDoesntExistException e) {
            return redirectWithMessage("danger","User doesn't exist");
        }
    }

    // and several other mappings that also call redirectWithMessage()

    public String redirectWithMessage(String status, String message) {
        // obtain RedirectAttributes somehow!
        redirectAttributes.addFlashAttribute("flashstatus",status);
        redirectAttributes.addFlashAttribute("flashmessage",message);
        return "redirect:/security";
    }

So the question is, how can the utility method (" redirectWithMessage ") obtain a pointer to RedirectAttributes without every method in the class having to have it in its signature and pass it along via injection?

Answer 1

You have a couple of ways with RequestContextUtils :

1. Call RequestContextUtils#getOutputFlashMap to get access to the flash map and update them (attributes + target redirect)

2. Call convenient method RequestContextUtils#saveOutputFlashMap

3. You can get instance of FlashMapManager

Invoke this method to write flash attributes:

Save the given FlashMap, in some underlying storage and set the start of its expiration period. NOTE: Invoke this method prior to a redirect in order to allow saving the FlashMap in the HTTP session or in a response cookie before the response is committed.

void saveOutputFlashMap(FlashMap flashMap, HttpServletRequest request, HttpServletResponse response)

You can gain access to current request/response by @Autowire them into the bean.

For your usecase, stick with #1 is OK (just add the attributes, the redirect location is set on your return string already)

Example:

@Autowired
HttpServletRequest request;

public String redirectWithMessage(String status, String message) {
   FlashMap flashMap = RequestContextUtils.getOutputFlashMap(request);

   flashMap.put("flashstatus",status);
   flashMap.put("flashmessage",message);

   return "redirect:/security";
}