Spring : Adding FlashAttribute in RedirectAttributes - spring

Question

I am new in spring and learning RedirectAttributes.Below is th sample code I am executing.
#RequestMapping(value="/")
public String app(Model model,RedirectAttributes rm) throws IOException{
UserCO userCO= new UserCO();
userCO.setEmail("rptdbay#gmail.com");
rm.addFlashAttribute("flashkey", "flashvalue");
rm.addFlashAttribute("userCO", userCO);
return "redirect:/controller1";
}
#RequestMapping(value="/controller1")
public String app1(Model model,HttpServletRequest request) throws IOException{
System.out.println("=====================================");
System.out.println("In Controller 1");
Map md = model.asMap();
for (Object modelKey : md.keySet()) {
Object modelValue = md.get(modelKey);
System.out.println("Model data =="+ modelKey + " -- " + modelValue);
}
java.util.Enumeration<String> reqEnum = request.getParameterNames();
while (reqEnum.hasMoreElements()) {
String s = reqEnum.nextElement();
System.out.println("Request data =="+ s+" : "+ request.getParameter(s));
}
return "redirect:/controller2";
}
#RequestMapping(value="/controller2")
public String app2(Model model,HttpServletRequest request) throws IOException{
System.out.println("=====================================");
System.out.println("In Controller 2");
Map md = model.asMap();
for (Object modelKey : md.keySet()) {
Object modelValue = md.get(modelKey);
System.out.println("Model data =="+ modelKey + " -- " + modelValue);
}
java.util.Enumeration<String> reqEnum = request.getParameterNames();
while (reqEnum.hasMoreElements()) {
String s = reqEnum.nextElement();
System.out.println("Request data =="+ s+" : "+ request.getParameter(s));
}
return "redirect:/controller3";
}
I have added String "flashvalue" and a object of bean userCO.I observed that-
Both "flashvalue" and userCO are available in Controller1.
Fine!,but in Controller2 "flashvalue" is available but userCO
not .Why so?
In Controller1 data is coming in Model ony but in Controller2 same
data is availavble in request only.Why so?
Below is my console log.
=====================================
In Controller 1
Model data ==userCO -- com.ttnd.mvc_mod.co.UserCO#60098260
Model data ==flashkey -- flashvalue
=====================================
In Controller 2
Request data ==flashkey : flashvalue
Is there any other way possible to get FlashAttribute rather than binding in Model?

Answer 1

First the explanation of your console log: You receive two model objects in controller 1. This is because you specify two flash attributes in method app. Flash attributes are stored in the HTTP session for the target controller, which retrieves it from there as model attributes. After that the flash attributes are erased by Spring.
In controller 2 the flash attributes are no longer available. The reason why “flashkey” is available in controller 2 as request attribute is, since primitive types in models are exposed as query parameters to the redirect target. As mentioned before, the flash attributes passed to controller 1 are exposed as model attributes. Your “userCO” is no primitive type, so you it will not get it as request parameter, while you will get “flashkey” as query parameter in controller 2.
If you want to switch off the “forward” of model objects as request parameters, set org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.setIgnoreDefaultModelOnRedirect(boolean) to true (as suggested by Spring for ‘new’ applications).
I don’t know whether there is another way to get flash attributes. I’d encourage you to not work around the concepts of Spring here but handle the flash attributes just like you did in your question. Think of flash attributes as model attributes in your redirect target. If you – for what reason – need two redirect until you reach your target, add the desired attributes a second time as flash attributes in controller 1.
See http://docs.spring.io/spring/docs/4.1.7.RELEASE/spring-framework-reference/html/mvc.html#mvc-ann-redirect-attributes and http://docs.spring.io/spring/docs/4.1.7.RELEASE/spring-framework-reference/html/mvc.html#mvc-flash-attributes for any details.