RedirectAttributes Flash scoped variables absent when redirecting using ResponseEntity [SPR-15176]

[spring-projects-issues]

Edward Smith opened SPR-15176 and commented

In short, when Flash scoped attributes are added in a @Controller method and then a redirect is executed by returning a type of ResponseEntity with an HTTP status of 302 Found, the Flash scoped attributes are lost.

See https://github.com/tednology/SPR-15176 for a working project demonstrating the bug.

@Controller
public class DemoController {
    
    @GetMapping("/bad")
    ResponseEntity<Void> bad(RedirectAttributes redirectAttributes) {
        redirectAttributes.addFlashAttribute("message", "Bad!");
        return ResponseEntity.status(HttpStatus.FOUND)
            .location(URI.create("/"))
            .build();
    }

    @GetMapping("/good")
    String good(RedirectAttributes redirectAttributes) {
        redirectAttributes.addFlashAttribute("message", "Good!");
        return "redirect:/";
    }

    @GetMapping("/")
    String home(Model model) {
        // Will print flash scoped message "Good!", but not "Bad!"
        model.asMap().entrySet().forEach(System.err::println);
        return "home";
    }
}

---

Affects: 4.3.4

Reference URL: https://github.com/tednology/SPR-15176

Referenced from: commits 5ea5f81

[spring-projects-issues]

Rossen Stoyanchev commented

RedirectAttributes, and also model attributes, are used when rendering through view resolution with a view and a model. Support for flash attributes was exposed through RedirectAttributes because it fits the redirect scenario but also because flash scope commonly comes up in browser applications for displaying a message after a post, etc. REST controllers tend to be more stateless.

So technically not a bug but rather an enhancement request. It shouldn't be hard to add. It's just a thin layer over the underlying FlashMapManager. That said I'm curious if you could share a little more about your use case.

[spring-projects-issues]

Edward Smith commented

Sure thing - I have written a helper library I used to manage messages of various severity levels (e.g. INFO / WARNING / ERROR / SUCCESS), in HTML views as you mentioned. Naturally I use redirect attributes / flash scope to preserve these messages across redirects.

I had a Controller class with mixed View rendering (e.g. String return types) and some REST-ish methods handling AJAX calls (methods with ResponseEntity<SomePayload> return types). I ended up writing a few POST handling methods which always result in redirects that were using a helper method ( return redirect("/location", statusCode) ) which built a ResponseEntity. Having been using ResponseEntity lately because I like the builder/explicit style, I just assumed that any redirection returned from a method in a controller would work with Flash scope.

So, having said all that, I don't have a special REST/stateful use case, so much as I was just expecting different behaviour.

Learned something new today - thanks for your quick feedback Rossen.

[spring-projects-issues]

Rossen Stoyanchev commented

Thanks for the extra details Edward Smith. Good to hear also about the preference to use ResponseEntity because of its API. Note that we are planning a similar API for view resolution purposes with #19775. That's for use on the reactive side, in the new WebFlux module but no reason why the same couldn't be applied to the WebMVC module as well.

[spring-projects-issues]

Edward Smith commented

Awesome, great to hear and thank you Rossen for the enhancement! VERY much looking forward to the Spring 5 GA.