Redirection setting parameters -redirectattributes

API Location ：https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/servlet/mvc/support/RedirectAttributes.html#:~:text=A RedirectAttributes model is empty when the method,of the controller that serves the target URL.

Basic use ：

 @RequestMapping(value = "/accounts", method = RequestMethod.POST)
 public String handle(Account account, BindingResult result, RedirectAttributes redirectAttrs) {
    
   if (result.hasErrors()) {
    
     return "accounts/new";
   }
   //  Redirect settings properties 
   redirectAttrs.addAttribute("id", account.getId()).addFlashAttribute("message", "Account created!");
   return "redirect:/accounts/{id}";
 }

There are two ways :（ In general use addFlashAttribute, Another kind of data is in the address bar , User visible , unsafe ）

• addAttribute： Reset back in url Put in the parameters ; Essentially, the request parameters are constructed based on your attributes , Then use the request parameters to redirect to the desired page , namely ：key1=val1&key2=val2…
  Use ：

  //  Do not convert to json, Report errors ：Cannot convert value of type 'java.util.HashMap' to required type 'java.lang.String'
  Map<String,String> val=new HashMap<>();
  ...
  redirectAttributes.addAttribute("key", JSONObject.toJSONString(val));
  

• addFlashAttribute： Put it in session in , It will be deleted after the first use
  Use

  Map<String,String> val=new HashMap<>();
  ...
  redirectAttributes.addFlashAttribute("key", val);