When you will be redirected to save the parameters SpringMVC (FlashMap)?

Save SpringMVC redirection parameters (FlashMap):
two cases will save the parameters:
    1. The current view RedirectView, is to say the current request is a redirection request.
        # renderMergedOutputModel RequestContextUtils.saveOutputFlashMap org.springframework.web.servlet.view.RedirectView (to targetUrl, Request, Response);!
        
    2. The current processing method HandlerMethod, the return value HttpEntity extension class (HttpEntity.class.isAssignableFrom (returnType after its execution .getParameterType ()) &&! RequestEntity.class.isAssignableFrom ( returnType.getParameterType ())).
        org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor # saveFlashAttributes RequestContextUtils.saveOutputFlashMap (location, req , res);!
    
internal tracking these two methods will eventually call org.springframework.web.servlet.support.SessionFlashMapManager #updateFlashMaps methods in order to save the FlashMap.