Question

I would like to know how to read a flash attributes after redirection in Spring MVC 3.1.

I have the following code:

@Controller
@RequestMapping("/foo")
public class FooController {

  @RequestMapping(value = "/bar", method = RequestMethod.GET)
  public ModelAndView handleGet(...) {
    // I want to see my flash attributes here!
  }

  @RequestMapping(value = "/bar", method = RequestMethod.POST)
  public ModelAndView handlePost(RedirectAttributes redirectAttrs) {
    redirectAttrs.addFlashAttributes("some", "thing");
    return new ModelAndView().setViewName("redirect:/foo/bar");
  }

}

What I am missing?

Answer 1

Use Model, it should have flash attributes prepopulated:

@RequestMapping(value = "/bar", method = RequestMethod.GET)
public ModelAndView handleGet(Model model) {
  String some = (String) model.asMap().get("some");
  // do the job
}

or, alternatively, you can use RequestContextUtils#getInputFlashMap:

@RequestMapping(value = "/bar", method = RequestMethod.GET)
public ModelAndView handleGet(HttpServletRequest request) {
  Map<String, ?> inputFlashMap = RequestContextUtils.getInputFlashMap(request);
  if (inputFlashMap != null) {
    String some = (String) inputFlashMap.get("some");
    // do the job
  }
}

P.S. You can do return return new ModelAndView("redirect:/foo/bar"); in handlePost.

EDIT:

JavaDoc says:

A RedirectAttributes model is empty when the method is called and is
never used unless the method returns a redirect view name or a
RedirectView.

It doesn’t mention ModelAndView, so maybe change handlePost to return "redirect:/foo/bar" string or RedirectView:

@RequestMapping(value = "/bar", method = RequestMethod.POST)
public RedirectView handlePost(RedirectAttributes redirectAttrs) {
  redirectAttrs.addFlashAttributes("some", "thing");
  return new RedirectView("/foo/bar", true);
}

I use RedirectAttributes in my code with RedirectView and model.asMap() method and it works OK.