Upasana | May 07, 2019 | 3 min read | 3,553 views
Duplicate form submission may happen due to wrong coding practice at the Spring MVC controller side. A poorly coded controller may cause duplicate form submission when a user hits F5 button after submitting the HTML form. PRG Web Design Pattern is specifically designed to get take care of this scenario.
You can use RedirectAttributes object which was introduced in Spring MVC 3.1 and populate it with data you want to keep for redirection. This is a very common usecase in web app development.
We shall always return a redirect view upon successful form submission in Spring MVC. This prevents duplicate form submission. Spring provides mechanism to pass attributes to redirected controller using RedirectAttributes.
@RequestMapping(value = "/accounts", method = RequestMethod.POST)
public String handle(Account account, BindingResult result, RedirectAttributes redirectAttrs) {
if (result.hasErrors()) {
return "accounts/new";
}
// Save account ...
redirectAttrs.addAttribute("id", account.getId()); (1)
redirectAttrs.addFlashAttribute("message", "Account created!"); (2)
return "redirect:/accounts/{id}";
}| 1 | attribute id will be added to request parameters after redirect. |
| 2 | attribute message will be stored inside flashmap inside session. |
addFlashAttribute actually stores the attributes in a flashmap which is internally maintained in the users session and removed once the next redirected request gets fulfilled.
on the other addAttribute essentially constructs request parameters out of your attributes and redirects to the desired page with the request parameters. So the advantage will be that you can store pretty much any object in your flash attribute(as it is not serialized into request params at all, but maintained as an object), whereas with addAttribute since the object that you add gets transformed to a normal request param, you are pretty limited to the object types like String or primitives.
A FlashMap provides a way for one request to store attributes intended for use in another. This is most commonly needed when redirecting from one URL to another — e.g. the Post/Redirect/Get pattern. A FlashMap is saved before the redirect (typically in the session) and is made available after the redirect and removed immediately.
A FlashMap can be set up with a request path and request parameters to help identify the target request. Without this information, a FlashMap is made available to the next request, which may or may not be the intended recipient. On a redirect, the target URL is known and a FlashMap can be updated with that information. This is done automatically when the org.springframework.web.servlet.view.RedirectView is used.
